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Setup ProxySQL as High Available (and not a SPOF)

During the last few months we had a lot of opportunities to present and discuss about a very powerful tool that will become more and more used in the architectures supporting MySQL, ProxySQL.

ProxySQL is becoming every day more flexible, solid, performant and used (http://www.proxysql.com/ and recent http://www.proxysql.com/compare).

This is it, the tool is a winner in comparing it with similar ones, and we all need to have a clear(er) idea on how integrate it in our architectures in order to achieve the best results.

The first to keep in mind is that ProxySQL is not natively supporting any high availability solution, in short we can setup a cluster of MySQL(s) and achieve 4 or even 5 nines of HA, but if we include ProxySQL, as it is, and as single block, our HA will include a single point of failure (SPOF) that will drag us down in case of crash.

To solve this, the most common solution so far had be to setup ProxySQL as part of a tile architecture, where Application/ProxySQL where deploy together.

tileProxy

This is a good solution for some cases, and for sure it reduce the network hops, but what it may be less than practical when our architecture has a very high number of tiles.
Say 100 or 400 application servers, not so unusual nowadays.
In that case managing the ProxySQL will be challenging, but most problematic it will be the fact that ProxySQL must perform several checks on the destination servers (MySQL), and if we have 400 instance of ProxySQL we will end up keeping our databases busy just because the checks.

In short ... is not a smart move.

Another possible approach, used so far was to have two layers of ProxySQL, one close to the application, another in the middle to finally connect to the database.

I personally don't like this approach for many reasons, but the most relevants are that this approach create additional complexity in the management of the platform, and it adds network hops.

ProxyCascade

So what can be done?

I like to have things simple, I love the KISS principle, I love to have things simple and because I am lazy I love to reuse the wheel instead re-invent things that someone else had already invent.

Last thing I like to have my customers not depending from me or any other colleague, once I am done, and gone, they must be able to manage their things, understand their things, fix their things by themselves.

Anyhow as said I like simple things. So my point here is the following:

excluding the cases where a tile (application/ProxySQL) make sense;
or when in the cloud and tools like ELB (Elastic load balancer) exist;
or on architecture already including a balancer.

What I can use for the remaining cases?

The answer comes with existing solutions and combining existing blocks, KeepAlived + ProxySQl + MySQL.

keepalived_logo

For KeepAlived explanation visit http://www.keepalived.org/.

Short description
"Keepalived is a routing software written in C. The main goal of this project is to provide simple and robust facilities for loadbalancing and high-availability to Linux system and Linux based infrastructures. Loadbalancing framework relies on well-known and widely used Linux Virtual Server (IPVS) kernel module providing Layer4 loadbalancing. Keepalived implements a set of checkers to dynamically and adaptively maintain and manage loadbalanced server pool according their health. On the other hand high-availability is achieved by VRRP protocol. VRRP is a fundamental brick for router failover. In addition, Keepalived implements a set of hooks to the VRRP finite state machine providing low-level and high-speed protocol interactions. Keepalived frameworks can be used independently or all together to provide resilient infrastructures."

Bingo! this is exactly what we need for our ProxySQL setup.

Below I will show how to setup:

Simple solution base on a single VIP
More complex solution using multiple VIPs
Even more complex solution using virtual VIPs and virtual servers.

Just remind that what we want to achieve is to prevent ProxySQL to become a SPOF, that's it.

While achieving that we need to reduce as much as possible the network hops and keep the solution SIMPLE.

Another important concept to keep in mind is that ProxySQL (re)start take place in less then a second.

This means that if it crash and it can be restarted by the angel process, having it doing so and recovery the service is much more efficient than to have any kind of failover mechanism to take place.

As such whenever you plan your solution keep in mind the ~1 second time of ProxySQL restart as base line.

Ready?

Let's go.

Setup

Choose 3 machines that will host the combination of Keepalive and ProxySQL.

In the following example I will use 3 machines for ProxySQL and Keepalived and 3 hosting PXC, but you can have the Keepalived+ProxySQL whenever you like also on the same PXC box.

For the following examples we will have:

PXC
node1 192.168.0.5 galera1h1n5
node2 192.168.0.21 galera2h2n21
node3 192.168.0.231 galera1h3n31
 
ProxySQL-Keepalived
test1 192.168.0.11
test2 192.168.0.12
test3 192.168.0.235
 
VIP 192.168.0.88 /89/90

To check I will use this table, please create it in your MySQL server:

DROP TABLE  test.`testtable2`;
 CREATE TABLE test.`testtable2` (
  `autoInc` bigint(11) NOT NULL AUTO_INCREMENT,
  `a` varchar(100) COLLATE utf8_bin NOT NULL,
  `b` varchar(100) COLLATE utf8_bin NOT NULL,
  `host` varchar(100) COLLATE utf8_bin NOT NULL,
  `userhost` varchar(100) COLLATE utf8_bin NOT NULL,
  PRIMARY KEY (`autoInc`)
) ENGINE=InnoDB ROW_FORMAT=DYNAMIC;

And this bash TEST command to use later

while [ 1 ];do export mydate=$(date +'%Y-%m-%d %H:%M:%S.%6N');

mysql --defaults-extra-file=./my.cnf -h 192.168.0.88 -P 3311  --skip-column-names

-b -e "BEGIN;set @userHost='a';select concat(user,'_', host) into @userHost from information_schema.processlist  where user = 'load_RW' limit 1;insert into test.testtable2 values(NULL,'$mydate',SYSDATE(6),@@hostname,@userHost);commit;select * from test.testtable2 order by 1 DESC limit 1" ;

sleep 1;done

Install ProxySQL (refer to https://github.com/sysown/proxysql/wiki#installation)
Install Keepalived (yum install keepalived; apt-get install keepalived)
Setup ProxySQL users and servers

Once you have your ProxySQL up (run the same on all ProxySQL nodes, it is much simpler), connect to the Admin interface and:

DELETE FROM mysql_replication_hostgroups WHERE writer_hostgroup=500 ;
DELETE FROM mysql_servers WHERE hostgroup_id IN (500,501);
 
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.0.5',500,3306,1000000000);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.0.5',501,3306,100);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.0.21',500,3306,1000000);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.0.21',501,3306,1000000000);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.0.231',500,3306,100);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.0.231',501,3306,1000000000);
LOAD MYSQL SERVERS TO RUNTIME; SAVE MYSQL SERVERS TO DISK;
 
DELETE FROM mysql_users WHERE username='load_RW';
INSERT INTO mysql_users (username,password,active,default_hostgroup,default_schema,transaction_persistent) VALUES ('load_RW','test',1,500,'test',1);
LOAD MYSQL USERS TO RUNTIME;SAVE MYSQL USERS TO DISK;
 
DELETE FROM mysql_query_rules WHERE rule_id IN (200,201);
INSERT INTO mysql_query_rules (rule_id,username,destination_hostgroup,active,retries,match_digest,apply) VALUES(200,'load_RW',501,1,3,'^SELECT.*FOR UPDATE',1);
INSERT INTO mysql_query_rules (rule_id,username,destination_hostgroup,active,retries,match_digest,apply) VALUES(201,'load_RW',501,1,3,'^SELECT ',1); 
 
LOAD MYSQL QUERY RULES TO RUNTIME;SAVE MYSQL QUERY RULES TO DISK;

Create a my.cnf file in your default dir with

[mysql]
user=load_RW
password=test

Simple Setup using a single VIP 3 ProxySQL 3 Galera nodes

proxy_keep_single

First setup the keepalive configuration file (/etc/keepalived/keepalived.conf):

global_defs {
  # Keepalived process identifier
  lvs_id proxy_HA
}
# Script used to check if Proxy is running
vrrp_script check_proxy {
  script "killall -0 proxysql"
  interval 2
  weight 2
}
# Virtual interface
# The priority specifies the order in which the assigned interface to take over in a failover
vrrp_instance VI_01 {
  state MASTER 
  interface em1
  virtual_router_id 51
  priority <calculate on the WEIGHT for each node>
 
  # The virtual ip address shared between the two loadbalancers
  virtual_ipaddress {
    192.168.0.88 dev em1
  }
  track_script {
    check_proxy
  }
}

Given the above and given I want to have test1 as main priority will be set as:

test1 = 101
test2 = 100
test3 = 99

Modify the config in each node following the above values and (re)start keepalived.

If all is set correctly in the system log of the TEST1 machine you will see:

Jan 10 17:56:56 mysqlt1 systemd: Started LVS and VRRP High Availability Monitor.
Jan 10 17:56:56 mysqlt1 Keepalived_healthcheckers[6183]: Configuration is using : 6436 Bytes
Jan 10 17:56:56 mysqlt1 Keepalived_healthcheckers[6183]: Using LinkWatch kernel netlink reflector...
Jan 10 17:56:56 mysqlt1 Keepalived_vrrp[6184]: Configuration is using : 63090 Bytes
Jan 10 17:56:56 mysqlt1 Keepalived_vrrp[6184]: Using LinkWatch kernel netlink reflector...
Jan 10 17:56:56 mysqlt1 Keepalived_vrrp[6184]: VRRP sockpool: [ifindex(2), proto(112), unicast(0), fd(10,11)]
Jan 10 17:56:56 mysqlt1 Keepalived_vrrp[6184]: VRRP_Script(check_proxy) succeeded
Jan 10 17:56:57 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Transition to MASTER STATE
Jan 10 17:56:57 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Received lower prio advert, forcing new election
Jan 10 17:56:57 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Received higher prio advert
Jan 10 17:56:57 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Entering BACKUP STATE
Jan 10 17:56:58 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) forcing a new MASTER election
...
Jan 10 17:57:00 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Transition to MASTER STATE
Jan 10 17:57:01 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Entering MASTER STATE <-- MASTER
Jan 10 17:57:01 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) setting protocol VIPs.
Jan 10 17:57:01 mysqlt1 Keepalived_healthcheckers[6183]: Netlink reflector reports IP 192.168.0.88 added
Jan 10 17:57:01 mysqlt1 avahi-daemon[937]: Registering new address record for 192.168.0.88 on em1.IPv4.
Jan 10 17:57:01 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Sending gratuitous ARPs on em1 for 192.168.0.88

While in the other two:

Jan 10 17:56:59 mysqlt2 Keepalived_vrrp[13107]: VRRP_Instance(VI_01) Entering BACKUP STATE <---

Which means node is there as ... :D Backup.

Now is time to test our connection to our ProxySQL pool.

From an application node or just from your laptop.

Open 3 terminals and in each one:

 watch -n 1 'mysql -h <IP OF THE REAL PROXY (test1|test2|test3)> -P 3310 -uadmin -padmin -t -e "select * from stats_mysql_connection_pool where hostgroup in (500,501,9500,9501) order by hostgroup,srv_host ;" -e " select srv_host,command,avg(time_ms), count(ThreadID) from stats_mysql_processlist group by srv_host,command;" -e "select * from stats_mysql_commands_counters where  Total_Time_us > 0;"'

You will see that unless you are already sending queries to proxies, you have the Proxies just doing nothing.
Time to start the test bash as I indicate above.
If everything is working correctly you will see the bash command reporting this:

+----+----------------------------+----------------------------+-------------+----------------------------+
| 49 | 2017-01-10 18:12:07.739152 | 2017-01-10 18:12:07.733282 | galera1h1n5 | load_RW_192.168.0.11:33273 |
+----+----------------------------+----------------------------+-------------+----------------------------+
  ID    execution time in the bash   exec time inside mysql     node hostname   user and where the connection is coming from

The other 3 running bash commands will show that ONLY the ProxySQL in TEST1 is currently getting/serving requests, because is the one with the VIP.

Like:

+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host      | srv_port | status | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.0.21  | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 629        |
| 500       | 192.168.0.231 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 510        |
| 500       | 192.168.0.5   | 3306     | ONLINE | 0        | 0        | 3      | 0       | 18      | 882             | 303             | 502        |
| 501       | 192.168.0.21  | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 629        |
| 501       | 192.168.0.231 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 510        |
| 501       | 192.168.0.5   | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 502        |
+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
+---------+---------------+-----------+-----------+-----------+---------+---------+----------+----------+-----------+-----------+--------+--------+---------+----------+
| Command | Total_Time_us | Total_cnt | cnt_100us | cnt_500us | cnt_1ms | cnt_5ms | cnt_10ms | cnt_50ms | cnt_100ms | cnt_500ms | cnt_1s | cnt_5s | cnt_10s | cnt_INFs |
+---------+---------------+-----------+-----------+-----------+---------+---------+----------+----------+-----------+-----------+--------+--------+---------+----------+
| BEGIN   | 9051          | 3         | 0         | 0         | 0       | 3       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| COMMIT  | 47853         | 3         | 0         | 0         | 0       | 0       | 0        | 3        | 0         | 0         | 0      | 0      | 0       | 0        |
| INSERT  | 3032          | 3         | 0         | 0         | 1       | 2       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| SELECT  | 8216          | 9         | 3         | 0         | 3       | 3       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| SET     | 2154          | 3         | 0         | 0         | 3       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
+---------+---------------+-----------+-----------+-----------+---------+---------+----------+----------+-----------+-----------+--------+--------+---------+----------+

So nothing special right, all as expected.

Time to see if the failover-failback works along the chain.

Let us kill the ProxySQL on TEST1 while the test bash command is running.

killall -9 proxysql

Here is what you will get:

+----+----------------------------+----------------------------+-------------+----------------------------+
| 91 | 2017-01-10 18:19:06.188233 | 2017-01-10 18:19:06.183327 | galera1h1n5 | load_RW_192.168.0.11:33964 |
+----+----------------------------+----------------------------+-------------+----------------------------+
ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.0.88' (111)
+----+----------------------------+----------------------------+-------------+----------------------------+
| 94 | 2017-01-10 18:19:08.250093 | 2017-01-10 18:19:11.250927 | galera1h1n5 | load_RW_192.168.0.12:39635 | <-- note 
+----+----------------------------+----------------------------+-------------+----------------------------+

the source had change but not the PXC node.

If you check the system log for TEST1:

Jan 10 18:19:06 mysqlt1 Keepalived_vrrp[6184]: VRRP_Script(check_proxy) failed
Jan 10 18:19:07 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Received higher prio advert
Jan 10 18:19:07 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) Entering BACKUP STATE
Jan 10 18:19:07 mysqlt1 Keepalived_vrrp[6184]: VRRP_Instance(VI_01) removing protocol VIPs.
Jan 10 18:19:07 mysqlt1 Keepalived_healthcheckers[6183]: Netlink reflector reports IP 192.168.0.88 removed

While on TEST2

Jan 10 18:19:08 mysqlt2 Keepalived_vrrp[13107]: VRRP_Instance(VI_01) Transition to MASTER STATE
Jan 10 18:19:09 mysqlt2 Keepalived_vrrp[13107]: VRRP_Instance(VI_01) Entering MASTER STATE
Jan 10 18:19:09 mysqlt2 Keepalived_vrrp[13107]: VRRP_Instance(VI_01) setting protocol VIPs.
Jan 10 18:19:09 mysqlt2 Keepalived_healthcheckers[13106]: Netlink reflector reports IP 192.168.0.88 added
Jan 10 18:19:09 mysqlt2 Keepalived_vrrp[13107]: VRRP_Instance(VI_01) Sending gratuitous ARPs on em1 for 192.168.0.88

Simple ... and elegant. No need to re-invent the wheel and works smooth.

The total time for the recovery given the ProxySQL crash had be of 5.06 seconds,

considering the wider window ( last application start, last recovery in PXC 2017-01-10 18:19:06.188233|2017-01-10 18:19:11.250927)

As such the worse scenario, keeping in mind we run the check for the ProxySQL every 2 seconds (real recover max window 5-2=3 sec).

OK what about fail-back?

Let us restart the proxysql service:

/etc/init.d/proxysql start (or systemctl)

Here the output:

+-----+----------------------------+----------------------------+-------------+----------------------------+
| 403 | 2017-01-10 18:29:34.550304 | 2017-01-10 18:29:34.545970 | galera1h1n5 | load_RW_192.168.0.12:40330 |
+-----+----------------------------+----------------------------+-------------+----------------------------+
+-----+----------------------------+----------------------------+-------------+----------------------------+
| 406 | 2017-01-10 18:29:35.597984 | 2017-01-10 18:29:38.599496 | galera1h1n5 | load_RW_192.168.0.11:34640 |
+-----+----------------------------+----------------------------+-------------+----------------------------+

Worse recovery time = 4.04 seconds of which 2 of delay because the check interval.

Of course the test is running every second and is running one single operation, as such the impact is minimal (no error in fail-back), and recovery longer.

But I think I have made clear the concept here.

Let see another thing... is the failover working as expected? Test1 -> 2 -> 3 ??

Let us kill 1 - 2 and see:

Kill Test1 :
+-----+----------------------------+----------------------------+-------------+----------------------------+
| 448 | 2017-01-10 18:35:43.092878 | 2017-01-10 18:35:43.086484 | galera1h1n5 | load_RW_192.168.0.11:35240 |
+-----+----------------------------+----------------------------+-------------+----------------------------+
+-----+----------------------------+----------------------------+-------------+----------------------------+
| 451 | 2017-01-10 18:35:47.188307 | 2017-01-10 18:35:50.191465 | galera1h1n5 | load_RW_192.168.0.12:40935 |
+-----+----------------------------+----------------------------+-------------+----------------------------+
...
Kill Test2
+-----+----------------------------+----------------------------+-------------+----------------------------+
| 463 | 2017-01-10 18:35:54.379280 | 2017-01-10 18:35:54.373331 | galera1h1n5 | load_RW_192.168.0.12:40948 |
+-----+----------------------------+----------------------------+-------------+----------------------------+
+-----+----------------------------+----------------------------+-------------+-----------------------------+
| 466 | 2017-01-10 18:36:08.603754 | 2017-01-10 18:36:09.602075 | galera1h1n5 | load_RW_192.168.0.235:33268 |
+-----+----------------------------+----------------------------+-------------+-----------------------------+

This image is where you should be at the end:

proxy_keep_single_failover

In this case given I have done one kill immediately after the other, Keepalived had take a bit more in failing over, but still it did correctly and following the planned chain.

Fail-back as smooth as usual:

+-----+----------------------------+----------------------------+-------------+-----------------------------+
| 502 | 2017-01-10 18:39:18.749687 | 2017-01-10 18:39:18.749688 | galera1h1n5 | load_RW_192.168.0.235:33738 |
+-----+----------------------------+----------------------------+-------------+-----------------------------+
+-----+----------------------------+----------------------------+-------------+----------------------------+
| 505 | 2017-01-10 18:39:19.794888 | 2017-01-10 18:39:22.800800 | galera1h1n5 | load_RW_192.168.0.11:35476 |
+-----+----------------------------+----------------------------+-------------+----------------------------+

Let us see now another case.

The case above is nice and simple, but as a cavet.

I can access only one ProxySQL a time, which may be good or not.

In any case it may be nice to have the possibility to choose, and with Keepalived you can.

We can actually set an X number of VIP and associate them to each test box.

The result will be that each server hosting ProxySQL will also host a VIP, and will be eventually able to fail-over to any of the other two servers.

proxy_keep_multiple

Failing-over/Back will be fully managed by Keepalived, checking as we did before if ProxySQL is running.
Example of configuration for one node can be the one below:

global_defs {
  # Keepalived process identifier
  lvs_id proxy_HA
}
# Script used to check if Proxy is running
vrrp_script check_proxy {
  script "killall -0 proxysql"
  interval 2
  weight 3
}
 
# Virtual interface 1
# The priority specifies the order in which the assigned interface to take over in a failover
vrrp_instance VI_01 {
  state MASTER
  interface em1
  virtual_router_id 51
  priority 102
 
  # The virtual ip address shared between the two loadbalancers
  virtual_ipaddress {
    192.168.0.88 dev em1
  }
  track_script {
    check_proxy
  }
}
 
# Virtual interface 2
# The priority specifies the order in which the assigned interface to take over in a failover
vrrp_instance VI_02 {
  state MASTER
  interface em1
  virtual_router_id 52
  priority 100
 
  # The virtual ip address shared between the two loadbalancers
  virtual_ipaddress {
    192.168.0.89 dev em1
  }
  track_script {
    check_proxy
  }
}
 
# Virtual interface 3
# The priority specifies the order in which the assigned interface to take over in a failover
vrrp_instance VI_03 {
  state MASTER
  interface em1
  virtual_router_id 53
  priority 99
 
  # The virtual ip address shared between the two loadbalancers
  virtual_ipaddress {
    192.168.0.90 dev em1
  }
  track_script {
    check_proxy
  }
}

The tricky part in this case is to play with the PRIORITY for each VIP and each server such that you will NOT assign the same ip twice.

The whole set of configs can be found here

Performing the check with the test bash as above we have:

Test 1 crash
+-----+----------------------------+----------------------------+-------------+----------------------------+
| 422 | 2017-01-11 18:30:14.411668 | 2017-01-11 18:30:14.344009 | galera1h1n5 | load_RW_192.168.0.11:55962 |
+-----+----------------------------+----------------------------+-------------+----------------------------+
ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.0.88' (111)
+-----+----------------------------+----------------------------+-------------+----------------------------+
| 426 | 2017-01-11 18:30:18.531279 | 2017-01-11 18:30:21.473536 | galera1h1n5 | load_RW_192.168.0.12:49728 | <-- new server
+-----+----------------------------+----------------------------+-------------+----------------------------+
....
Test 2 crash
+-----+----------------------------+----------------------------+-------------+----------------------------+
| 450 | 2017-01-11 18:30:27.885213 | 2017-01-11 18:30:27.819432 | galera1h1n5 | load_RW_192.168.0.12:49745 |
+-----+----------------------------+----------------------------+-------------+----------------------------+
ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.0.88' (111)
+-----+----------------------------+----------------------------+-------------+-----------------------------+
| 454 | 2017-01-11 18:30:30.971708 | 2017-01-11 18:30:37.916263 | galera1h1n5 | load_RW_192.168.0.235:33336 | <-- new server
+-----+----------------------------+----------------------------+-------------+-----------------------------+

Final state of IPs on Test3:

enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:c2:16:3f brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.235/24 brd 192.168.0.255 scope global enp0s8   <-- Real IP
       valid_lft forever preferred_lft forever
    inet 192.168.0.90/32 scope global enp0s8    <--- VIP 3
       valid_lft forever preferred_lft forever
    inet 192.168.0.89/32 scope global enp0s8    <--- VIP 2
       valid_lft forever preferred_lft forever
    inet 192.168.0.88/32 scope global enp0s8    <--- VIP 1
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fec2:163f/64 scope link 
       valid_lft forever preferred_lft forever

And this is the image:

proxy_keep_multiple_full_failover

Recovery times:

  test 1 crash = 7.06 sec (worse case scenario)
  test 2 crash = 10.03 sec (worse case scenario)

Conclusions

In this example I had just use a test that checks the process, but a check can be anything reporting 0|1, the limit is define only from what you need.

The times for the failover can be significant shorter, reducing the check time and considering only the time taken to move the VIP, I had prefer to show the worse case scenario considering an application with a second interval, but that is a pessimistic view of what normally happens with real traffic.

I was looking for a simple, simple simple way to add HA to ProxySQL, something that can be easily integrate with automation and that is actually also well established and maintained.

In my opinion using Keepalived is a good solution because it match all the above expectations.

Implementing a set of ProxySQL and have Keepalived manage the failover between them is pretty easy, but you can expand the usage (and the complexity) if you need, counting on tools that are already part of the Linux stack, no need to re-invent the wheel with crazy mechanism.

If you want to have fun doing crazy things... at least start from something that helps you to go beyond the basiscs.

For instance I was also playing a bit with keepalived and virtual server, creating set of redundant Proxysql with load balancers and ... .. but this is another story (blog).

Great MySQL & ProxySQL to all!

ProxySQL – Percona Cluster (Galera) integration

ProxySQL is design to do not perform any specialized operation in relation to the servers it communicate with.

Instead it has scheduled events that can be used to extend functionalities and cover any special need.

Given that specialized product like PXC, are not managed by ProxySQL and require the design and implementation of good/efficient extensions.

In this article I will illustrate how PXC/Galera can be integrated with ProxySQL to get the best from both.

Brief digression

Before discussing the PXC integration, we need to review a couple of very important concept in ProxySQL.ProxySQL has a very important logical component, the Hostgroup(s) (HG).
An hostgroup as a relation of :

+-----------+       +------------------------+
|Host group +------>|Server (1:N)            |
+-----------+       +------------------------+

Not only, in ProxySQL you can use QueryRules (QR) that can be directly map to an HG.

Such that you can define a specific user to go ONLY to that HG, for instance you may want to have user app1_user go only on Servers A-B-C.

The only thing you need to do is to set a QR that say this user (app1_user) had destination hostgroup 5.

Where HG 5 has the servers A-B-C.

INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.5',5,3306,10);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.6',5,3306,10);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.7',5,3306,10);
INSERT INTO mysql_query_rules (username,destination_hostgroup,active) VALUES('app1_user',5,1);

Easy isn't it?

Another important concept in ProxySQL also related to HG is ReplicationHostgroup(s) (RHG).

This is a special HG that ProxySQL use to automatically manage the nodes that are connected by replication and configured in Write/Read and Read_only mode.

What it means?

Let us say you have 4 nodes A-B-C-D, connected by standard asynchronous replication.

Where A is the master and B-C-D are the slaves.

What you want is to have you application pointing to server A for all writes, and to B-C the reads keeping off D because is a backup slave.

Also you don't want to have any read to go to B-C if the replication delay is more than 2 seconds.

Using RHG in conjunction with HG, ProxySQL will manage all these for you.

To achieve that we only have to instruct proxy to:use RHGdefine the value of the maximum latencyUsing the example above:

INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.5',5,3306,10,2);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.6',5,3306,10,2);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.7',5,3306,10,2);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.8',10,3306,10,2);
INSERT INTO mysql_query_rules (username,destination_hostgroup,active) VALUES('app1_user',5,1);
INSERT INTO mysql_query_rules (username,destination_hostgroup,active) VALUES('app1_user',6,1);
INSERT INTO mysql_replication_hostgroups VALUES (5,6);

From now on ProxySQL will split the R/W using the RHG and the nodes defined in HG 5.

The flexibility that the use of the HG introduce, is obviously not limited to what I had mention here, and will play a good part in the integration between PXC and ProxySQL that I will illustrate below.

PXC/Galera integration

In a PXC cluster a node can have many different state and conditions that will affect if and if yes how, your application should operate on the node.

The most common one is when a node become a DONOR.

Whoever had install PXC or any Galera implementation, had face that when a node become a DONOR it will change it state to DESYNC, and/or if the node is heavy loaded, the DONOR process may affect the node itself.

But that is just one of the thing.

A node can be in state 3 JOINED but not sync, it can have wsrep_rejectqueries, wsrep_donorrejectqueries, wsrep_ready (off), it can be in a different segment and last but not least the number of nodes per segment is relevant.

To show what can be done, and how, we will use the following setup:

5 nodes

2 segment

Applications requiring R/W split

And finally two options:

single writer node

multiple writers node

What will analyze here is how Proxy will behave under the use of a script run by the ProxySQL scheduler.

The use of a script is necessary to have ProxySQL act correctly to PXC state modifications.

ProxySQL comes with two scripts for galera, both of them are too basic and not considering a lot of relevant conditions.

As example I have wrote a more complete script https://github.com/Tusamarco/proxy_sql_tools galera_check.pl

The script is designed to manage a X number of nodes that belong to a given Hostgroup (HG).

The script works by HG and as such it will perform isolated actions/checks by HG.

It is not possible to have more than one check running on the same HG.

The check will create a lock file {proxysql_galera_check_${hg}.pid} that will be used by the check to prevent duplicates.

Galera_check will connect to the ProxySQL node and retrieve all the information regarding the Nodes/proxysql configuration.

It will then check in parallel each node and will retrieve the status and configuration.At the moment galera_check analyze and manage the following:

Node states:

read_only

wsrep_status

wsrep_rejectqueries

wsrep_donorrejectqueries

wsrep_connected

wsrep_desinccount

wsrep_ready

wsrep_provider

wsrep_segment

Number of nodes in by segment

Retry loop

As mention the number of Nodes inside a segment is relevant, if a node is the only one in a segment, the check will behave accordingly.

IE if a node is the only one in the MAIN segment, it will not put the node in OFFLINE_SOFT when the node become donor to prevent the cluster to become unavailable for the applications.

In the script it is possible to declare a segment as MAIN, quite useful when managing prod and DR site, because the script will manage the segment acting as main in a more conservative way.

The check can be configured to perform retries after a given interval.

Where the interval is the time define in the ProxySQL scheduler.

As such if the check is set to have 2 retry for UP and 3 for down, it will loop that number before doing anything.PXC/Galera does some action behind the hood, some of them not totally correct.

This feature is useful in some not well known cases where Galera behave weird.

IE whenever a node is set to READ_ONLY=1, galera desync and resync the node.

A check not taking this into account will cause a node to be set OFFLINE and back for no reason.

Another important differentiation for this check is that it use special HGs for maintenance, all in range of 9000.

So if a node belong to HG 10 and the check needs to put it in maintenance mode, the node will be moved to HG 9010.

Once all is normal again, the Node will be put back on his original HG. This check does NOT modify any state of the Nodes.

Meaning It will NOT modify any variables or settings in the original node.

It will ONLY change node states in ProxySQL.

Multiwriter mode

The MOST and recommended way to use galera is to have it in multiwriter mode.

Then play with the weight to have a node act as MAIN node and prevent/reduce certification failures and Brutal force Abort from PXC.

The configuration to use is:

DELETE FROM mysql_replication_hostgroups WHERE writer_hostgroup=500 ;
DELETE FROM mysql_servers WHERE hostgroup_id IN (500,501);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.5',500,3306,1000000000);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.5',501,3306,100);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.6',500,3306,1000000);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.6',501,3306,1000000000);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.7',500,3306,100);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.7',501,3306,1000000000);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.8',500,3306,1);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.8',501,3306,1);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.9',500,3306,1);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.9',501,3306,1);
LOAD MYSQL SERVERS TO RUNTIME; SAVE MYSQL TO DISK;

In this test we will NOT use Replication HostGroup.

We will do that later when testing single writer, for now ... focus on multi-writer.

Segment 1 cover HG 500 and 501 while segment 2 is only 501.
Weight for servers in HG 500 is progressive from 1 to 1 billion, this to reduce the possible random writes on the non main node.

As such Nodes:

HG 500
S1 192.168.1.5 - 1.000.000.000
S1 192.168.1.6 - 1.000.000
S1 192.168.1.7 - 100
S2 192.168.1.8 - 1
S2 192.168.1.9 - 1
 
HG 501
S1 192.168.1.5 - 100
S1 192.168.1.6 - 1000000000
S1 192.168.1.7 - 1000000000
S2 192.168.1.8 - 1
S2 192.168.1.9 - 1

The following command can be used to view what ProxySQL is doing:

watch -n 1 'mysql -h 127.0.0.1 -P 3310 -uadmin -padmin -t -e "select * from stats_mysql_connection_pool where hostgroup in (500,501,9500,9501) order by hostgroup,srv_host ;" -e " select hostgroup_id,hostname,status,weight,comment from mysql_servers where hostgroup_id in (500,501,9500,9501)  order by hostgroup_id,hostname ;"'

Download the check from git (https://github.com/Tusamarco/proxy_sql_tools) and activate it in ProxySQL.

Be sure to set the parameter that match your installation:

DELETE FROM scheduler WHERE id=10;
INSERT  INTO scheduler (id,active,interval_ms,filename,arg1) VALUES (10,0,2000,"/var/lib/proxysql/galera_check.pl","-u=admin -p=admin -h=192.168.1.50 -H=500:W,501:R -P=3310 --execution_time=1 --retry_down=2 --retry_up=1 --main_segment=1 --debug=0  --log=/var/lib/proxysql/galeraLog");
LOAD SCHEDULER TO RUNTIME;SAVE SCHEDULER TO DISK;

If you want activate it:

UPDATE scheduler SET active=1 WHERE id=10;
LOAD SCHEDULER TO RUNTIME;

The following is the kind of scenario we have:

+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.9 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 413        |
| 500       | 192.168.1.8 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 420        |
| 500       | 192.168.1.7 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 227        |
| 500       | 192.168.1.6 | 3306     | ONLINE | 0        | 10       | 10     | 0       | 12654    | 1016975         | 0               | 230        |
| 500       | 192.168.1.5 | 3306     | ONLINE | 0        | 9        | 29     | 0       | 107358   | 8629123         | 0               | 206        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 0        | 4        | 6      | 0       | 12602425 | 613371057       | 34467286486     | 413        |
| 501       | 192.168.1.8 | 3306     | ONLINE | 0        | 6        | 7      | 0       | 12582617 | 612422028       | 34409606321     | 420        |
| 501       | 192.168.1.7 | 3306     | ONLINE | 0        | 6        | 6      | 0       | 18580675 | 905464967       | 50824195445     | 227        |
| 501       | 192.168.1.6 | 3306     | ONLINE | 0        | 6        | 14     | 0       | 18571127 | 905075154       | 50814832276     | 230        |
| 501       | 192.168.1.5 | 3306     | ONLINE | 0        | 1        | 10     | 0       | 169570   | 8255821         | 462706881       | 206        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+

To generate load we will use the following commands (or whatever you like but do 2 different for read only and reads/writes)

Write
sysbench --test=/usr/share/doc/sysbench/tests/db/oltp.lua --mysql-host=192.168.1.50 --mysql-port=3311 --mysql-user=stress_RW --mysql-password=test --mysql-db=test_galera --db-driver=mysql --oltp-tables-count=50 --oltp-tablesize=50000 --max-requests=0 --max-time=9000 --oltp-point-selects=5 --oltp-read-only=off --oltp-dist-type=uniform --oltp-reconnect-mode=transaction --oltp-skip-trx=off --num-threads=10 --report-interval=10 --mysql-ignore-errors=all run
Read only
sysbench --test=/usr/share/doc/sysbench/tests/db/oltp.lua --mysql-host=192.168.1.50 --mysql-port=3311 --mysql-user=stress_RW --mysql-password=test --mysql-db=test_galera --db-driver=mysql --oltp-tables-count=50 --oltp-tablesize=50000 --max-requests=0 --max-time=9000 --oltp-point-selects=5 --oltp-read-only=on --num-threads=10 --oltp-reconnect-mode=query --oltp-skip-trx=on --report-interval=10 --mysql-ignore-errors=all run

Now the most common thing that could happen to a cluster node is to become a donor, this is a planned activity for a PXC, and it is suppose to be manage in the less harmful way.

To simulate that we will choose a node and crash it, forcing the crash node to elect as DONOR our main node (the one with highest WEIGHT).

To do so we need to have the parameter wsrep_sst_donor set in the node that will request the SST data transfer.

SHOW global VARIABLES LIKE 'wsrep_sst_donor';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| wsrep_sst_donor | node1 | <---
+-----------------+-------+

Activate the check if not already done:

UPDATE scheduler SET active=1 WHERE id=10;

And now run traffic.

Then check load:

SELECT * FROM stats_mysql_connection_pool WHERE hostgroup IN (500,501,9500,9501) ORDER BY hostgroup,srv_host ;
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 10       | 0        | 30     | 0       | 112662   | 9055479         | 0               | 120        | <--- our Donor
| 500       | 192.168.1.6 | 3306     | ONLINE | 0        | 10       | 10     | 0       | 12654    | 1016975         | 0               | 111        |
| 500       | 192.168.1.7 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 115        |
| 500       | 192.168.1.8 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 316        |
| 500       | 192.168.1.9 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 329        |
| 501       | 192.168.1.5 | 3306     | ONLINE | 0        | 1        | 10     | 0       | 257271   | 12533763        | 714473854       | 120        |
| 501       | 192.168.1.6 | 3306     | ONLINE | 0        | 10       | 18     | 0       | 18881582 | 920200116       | 51688974309     | 111        |
| 501       | 192.168.1.7 | 3306     | ONLINE | 3        | 6        | 9      | 0       | 18927077 | 922317772       | 51794504662     | 115        |
| 501       | 192.168.1.8 | 3306     | ONLINE | 0        | 1        | 8      | 0       | 12595556 | 613054573       | 34447564440     | 316        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 1        | 3        | 6      | 0       | 12634435 | 614936148       | 34560620180     | 329        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+

On one of the node:

kill mysql

remove the content of the data directory

restart the node

The node will go in SST and our galera_check script will manage it:

+--------------+-------------+--------------+------------+--------------------------------------------------+
| hostgroup_id | hostname    | STATUS       | weight     | comment                                          |
+--------------+-------------+--------------+------------+--------------------------------------------------+
| 500          | 192.168.1.5 | OFFLINE_SOFT | 1000000000 | 500_W_501_R_retry_up=0;500_W_501_R_retry_down=0; | <---- the donor
| 500          | 192.168.1.6 | ONLINE       | 1000000    |                                                  |
| 500          | 192.168.1.7 | ONLINE       | 100        |                                                  |
| 500          | 192.168.1.8 | ONLINE       | 1          |                                                  |
| 500          | 192.168.1.9 | ONLINE       | 1          |                                                  |
| 501          | 192.168.1.5 | OFFLINE_SOFT | 100        | 500_W_501_R_retry_up=0;500_W_501_R_retry_down=0; |
| 501          | 192.168.1.6 | ONLINE       | 1000000000 |                                                  |
| 501          | 192.168.1.7 | ONLINE       | 1000000000 |                                                  |
| 501          | 192.168.1.8 | ONLINE       | 1          |                                                  |
| 501          | 192.168.1.9 | ONLINE       | 1          |                                                  |
+--------------+-------------+--------------+------------+--------------------------------------------------+

We can also check the galera_check log and see what happened:

2016/09/02 16:13:27.298:[WARN] Move node:192.168.1.5;3306;500;3010 SQL: UPDATE mysql_servers SET status='OFFLINE_SOFT' WHERE hostgroup_id=500 AND hostname='192.168.1.5' AND port='3306'
2016/09/02 16:13:27.303:[WARN] Move node:192.168.1.5;3306;501;3010 SQL: UPDATE mysql_servers SET status='OFFLINE_SOFT' WHERE hostgroup_id=501 AND hostname='192.168.1.5' AND port='3306'

The node will remain in OFFLINE_SOFT while the other node (192.168.1.6 having the 2nd WEIGHT) serves the writes, untill the node is in DONOR state.

All as expected, the node was set in OFFLINE_SOFT state, which mean the existing connections where able to finish, whole the node was not accepting any NEW connection.

As soon the node ends to send data to the Joiner, it was moved back and traffic restart:

2016/09/02 16:14:58.239:[WARN] Move node:192.168.1.5;3306;500;1000 SQL: UPDATE mysql_servers SET STATUS='ONLINE' WHERE hostgroup_id=500 AND hostname='192.168.1.5' AND port='3306'
2016/09/02 16:14:58.243:[WARN] Move node:192.168.1.5;3306;501;1000 SQL: UPDATE mysql_servers SET STATUS='ONLINE' WHERE hostgroup_id=501 AND hostname='192.168.1.5' AND port='3306'
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 6        | 1        | 37     | 0       | 153882   | 12368557        | 0               | 72         | <---
| 500       | 192.168.1.6 | 3306     | ONLINE | 1        | 9        | 10     | 0       | 16008    | 1286492         | 0               | 42         |
| 500       | 192.168.1.7 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 1398     | 112371          | 0               | 96         |
| 500       | 192.168.1.8 | 3306     | ONLINE | 0        | 0        | 24545  | 791     | 24545    | 122725          | 0               | 359        |
| 500       | 192.168.1.9 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 15108    | 1214366         | 0               | 271        |
| 501       | 192.168.1.5 | 3306     | ONLINE | 1        | 0        | 11     | 0       | 2626808  | 128001112       | 7561278884      | 72         |
| 501       | 192.168.1.6 | 3306     | ONLINE | 5        | 7        | 20     | 0       | 28629516 | 1394974468      | 79289633420     | 42         |
| 501       | 192.168.1.7 | 3306     | ONLINE | 2        | 8        | 10     | 0       | 29585925 | 1441400648      | 81976494740     | 96         |
| 501       | 192.168.1.8 | 3306     | ONLINE | 0        | 0        | 16779  | 954     | 12672983 | 616826002       | 34622768228     | 359        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 0        | 4        | 6      | 0       | 13567512 | 660472589       | 37267991677     | 271        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+

This was easy, and more or less managed also by the standard script.

But what would happened if my donor was set to DO NOT serve query when in donor state?

Wait what?? Yes PXC (Galera in general) can be set to refuse any query when the Node goes in DONOR state.

If not managed this will cause issue because the Node will simply reject queries but ProxySQL see he node alive.

Let me show you:

SHOW global VARIABLES LIKE 'wsrep_sst_donor_rejects_queries';
+---------------------------------+-------+
| Variable_name                   | Value |
+---------------------------------+-------+
| wsrep_sst_donor_rejects_queries | ON    |
+---------------------------------+-------+

For a moment let us deactivate the check.

Then, do the same stop and delete of the data dir, then restart the node... SST take place.

And sysbench will report:

ALERT: mysql_drv_query() returned error 2013 (Lost connection to MySQL server during query) for query 'BEGIN'
FATAL: failed to execute function `event': 3
ALERT: mysql_drv_query() returned error 2013 (Lost connection to MySQL server during query) for query 'BEGIN'
FATAL: failed to execute function `event': 3

But and ProxySQL?

+-----------+-------------+----------+---------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS  | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+---------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE  | 0        | 0        | 101    | 0       | 186331   | 14972717        | 0               | 118        | <-- no writes in wither HG
| 500       | 192.168.1.6 | 3306     | ONLINE  | 0        | 9        | 10     | 0       | 20514    | 1648665         | 0               | 171        |  |
| 500       | 192.168.1.7 | 3306     | ONLINE  | 0        | 1        | 3      | 0       | 5881     | 472629          | 0               | 134        |  |
| 500       | 192.168.1.8 | 3306     | ONLINE  | 0        | 0        | 205451 | 1264    | 205451   | 1027255         | 0               | 341        |  |
| 500       | 192.168.1.9 | 3306     | ONLINE  | 0        | 1        | 2      | 0       | 15642    | 1257277         | 0               | 459        |  -
| 501       | 192.168.1.5 | 3306     | ONLINE  | 1        | 0        | 13949  | 0       | 4903347  | 238627310       | 14089708430     | 118        |
| 501       | 192.168.1.6 | 3306     | ONLINE  | 2        | 10       | 20     | 0       | 37012174 | 1803380964      | 103269634626    | 171        |
| 501       | 192.168.1.7 | 3306     | ONLINE  | 2        | 11       | 13     | 0       | 38782923 | 1889507208      | 108288676435    | 134        |
| 501       | 192.168.1.8 | 3306     | SHUNNED | 0        | 0        | 208452 | 1506    | 12864656 | 626156995       | 34622768228     | 341        |
| 501       | 192.168.1.9 | 3306     | ONLINE  | 1        | 3        | 6      | 0       | 14451462 | 703534884       | 39837663734     | 459        |
+-----------+-------------+----------+---------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
mysql> SELECT * FROM mysql_server_connect_log WHERE hostname IN ('192.168.1.5','192.168.1.6','192.168.1.7','192.168.1.8','192.168.1.9')  ORDER BY time_start_us DESC LIMIT 10;
+-------------+------+------------------+-------------------------+--------------------------------------------------------------------------------------------------------+
| hostname    | port | time_start_us    | connect_success_time_us | connect_error                                                                                          |
+-------------+------+------------------+-------------------------+--------------------------------------------------------------------------------------------------------+
| 192.168.1.9 | 3306 | 1472827444621954 | 1359                    | NULL                                                                                                   |
| 192.168.1.8 | 3306 | 1472827444618883 | 0                       | Can't connect to MySQL server on '192.168.1.8' (107)                                                   |
| 192.168.1.7 | 3306 | 1472827444615819 | 433                     | NULL                                                                                                   |
| 192.168.1.6 | 3306 | 1472827444612722 | 538                     | NULL                                                                                                   |
| 192.168.1.5 | 3306 | 1472827444606560 | 473                     | NULL                                                                                                   | <-- donor is seen as up
| 192.168.1.9 | 3306 | 1472827384621463 | 1286                    | NULL                                                                                                   |
| 192.168.1.8 | 3306 | 1472827384618442 | 0                       | Lost connection to MySQL server at 'handshake: reading inital communication packet', system error: 107 |
| 192.168.1.7 | 3306 | 1472827384615317 | 419                     | NULL                                                                                                   |
| 192.168.1.6 | 3306 | 1472827384612241 | 415                     | NULL                                                                                                   |
| 192.168.1.5 | 3306 | 1472827384606117 | 454                     | NULL                                                                                                   | <-- donor is seen as up
+-------------+------+------------------+-------------------------+--------------------------------------------------------------------------------------------------------+
select * from mysql_server_ping_log where hostname in ('192.168.1.5','192.168.1.6','192.168.1.7','192.168.1.8','192.168.1.9')  order by time_start_us desc limit 10;
+-------------+------+------------------+----------------------+------------------------------------------------------+
| hostname    | port | time_start_us    | ping_success_time_us | ping_error                                           |
+-------------+------+------------------+----------------------+------------------------------------------------------+
| 192.168.1.9 | 3306 | 1472827475062217 | 311                  | NULL                                                 |
| 192.168.1.8 | 3306 | 1472827475060617 | 0                    | Can't connect TO MySQL server ON '192.168.1.8' (107) |
| 192.168.1.7 | 3306 | 1472827475059073 | 108                  | NULL                                                 |
| 192.168.1.6 | 3306 | 1472827475057281 | 102                  | NULL                                                 |
| 192.168.1.5 | 3306 | 1472827475054188 | 74                   | NULL                                                 | <-- donor is seen as up
| 192.168.1.9 | 3306 | 1472827445061877 | 491                  | NULL                                                 |
| 192.168.1.8 | 3306 | 1472827445060254 | 0                    | Can't connect to MySQL server on '192.168.1.8' (107) |
| 192.168.1.7 | 3306 | 1472827445058688 | 53                   | NULL                                                 |
| 192.168.1.6 | 3306 | 1472827445057124 | 131                  | NULL                                                 |
| 192.168.1.5 | 3306 | 1472827445054015 | 98                   | NULL                                                 | <-- donor is seen as up
+-------------+------+------------------+----------------------+------------------------------------------------------+

As you can see all seems ok also if it is not :)

Let us turn on the galera_check and see what happens.

Run some load in read and write.

And now let me do the stop-delete-restart-SST process again

kill -9 <mysqld_safe_pid> <mysqld_pid>; rm -fr data/*;rm -fr logs/*;sleep 2;./start

A soon the node goes down ProxySQL Shun the node.

+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS  | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE  | 7        | 3        | 34     | 0       | 21570   | 1733833         | 0               | 146        |
| 500       | 192.168.1.6 | 3306     | ONLINE  | 1        | 8        | 12     | 0       | 9294    | 747063          | 0               | 129        |
| 500       | 192.168.1.7 | 3306     | ONLINE  | 1        | 0        | 4      | 0       | 3396    | 272950          | 0               | 89         |
| 500       | 192.168.1.8 | 3306     | SHUNNED | 0        | 0        | 1      | 6       | 12      | 966             | 0               | 326        | <-- crashed
| 500       | 192.168.1.9 | 3306     | ONLINE  | 1        | 0        | 2      | 0       | 246     | 19767           | 0               | 286        |
| 501       | 192.168.1.5 | 3306     | ONLINE  | 0        | 1        | 2      | 0       | 772203  | 37617973        | 2315131214      | 146        |
| 501       | 192.168.1.6 | 3306     | ONLINE  | 9        | 3        | 12     | 0       | 3439458 | 167514166       | 10138636314     | 129        |
| 501       | 192.168.1.7 | 3306     | ONLINE  | 1        | 12       | 13     | 0       | 3183822 | 155064971       | 9394612877      | 89         |
| 501       | 192.168.1.8 | 3306     | SHUNNED | 0        | 0        | 1      | 6       | 11429   | 560352          | 35350726        | 326        | <-- crashed
| 501       | 192.168.1.9 | 3306     | ONLINE  | 0        | 1        | 1      | 0       | 312253  | 15227786        | 941110520       | 286        |
+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

Immediately after the glera_check identify the node is requesting the SST and that the DONOR is our writer, given is NOT the only writer in the HG, and given it has the variable wsrep_sst_donor_rejects_queries active, it cannot be set OFFLINE_SOFT, and we do not want to have ProxySQL consider it OFFLINE_HARD (because it is not).
As such the script will move it to a special HG:

2016/09/04 16:11:22.091:[WARN] Move node:192.168.1.5;3306;500;3001 SQL: UPDATE mysql_servers SET hostgroup_id=9500 WHERE hostgroup_id=500 AND hostname='192.168.1.5' AND port='3306'
2016/09/04 16:11:22.097:[WARN] Move node:192.168.1.5;3306;501;3001 SQL: UPDATE mysql_servers SET hostgroup_id=9501 WHERE hostgroup_id=501 AND hostname='192.168.1.5' AND port='3306'
+--------------+-------------+------+--------+------------+-------------+-----------------+---------------------+---------+----------------+--------------------------------------------------+
| hostgroup_id | hostname    | port | STATUS | weight     | compression | max_connections | max_replication_lag | use_ssl | max_latency_ms | comment                                          |
+--------------+-------------+------+--------+------------+-------------+-----------------+---------------------+---------+----------------+--------------------------------------------------+
| 500          | 192.168.1.6 | 3306 | ONLINE | 1000000    | 0           | 1000            | 0                   | 0       | 0              |                                                  |
| 500          | 192.168.1.7 | 3306 | ONLINE | 100        | 0           | 1000            | 0                   | 0       | 0              |                                                  |
| 500          | 192.168.1.8 | 3306 | ONLINE | 1          | 0           | 1000            | 0                   | 0       | 0              | 500_W_501_R_retry_up=0;500_W_501_R_retry_down=0; |
| 500          | 192.168.1.9 | 3306 | ONLINE | 1          | 0           | 1000            | 0                   | 0       | 0              | 500_W_501_R_retry_up=0;500_W_501_R_retry_down=0; |
| 501          | 192.168.1.6 | 3306 | ONLINE | 1000000000 | 0           | 1000            | 0                   | 0       | 0              |                                                  |
| 501          | 192.168.1.7 | 3306 | ONLINE | 1000000000 | 0           | 1000            | 0                   | 0       | 0              |                                                  |
| 501          | 192.168.1.9 | 3306 | ONLINE | 1          | 0           | 1000            | 0                   | 0       | 0              | 500_W_501_R_retry_up=0;500_W_501_R_retry_down=0; |
| 9500         | 192.168.1.5 | 3306 | ONLINE | 1000000000 | 0           | 1000            | 0                   | 0       | 0              | 500_W_501_R_retry_up=0;500_W_501_R_retry_down=0; | <-- Special HG
| 9501         | 192.168.1.5 | 3306 | ONLINE | 100        | 0           | 1000            | 0                   | 0       | 0              | 500_W_501_R_retry_up=0;500_W_501_R_retry_down=0; | <-- Special HG
+--------------+-------------+------+--------+------------+-------------+-----------------+---------------------+---------+----------------+--------------------------------------------------+

In this way the Donor will continue to serve the Joiner, but applications will not see it.

What is also very important is what the applications will see.

The Applications doing WRITEs will see:

[ 10s] threads: 10, tps: 9.50, reads: 94.50, writes: 42.00, response time: 1175.77ms (95%), errors: 0.00, reconnects: 0.00
...
[ 40s] threads: 10, tps: 2.80, reads: 26.10, writes: 11.60, response time: 3491.45ms (95%), errors: 0.00, reconnects: 0.10
[ 50s] threads: 10, tps: 4.80, reads: 50.40, writes: 22.40, response time: 10062.13ms (95%), errors: 0.80, reconnects: 351.60 <--- Main writer moved to another HG
[ 60s] threads: 10, tps: 5.90, reads: 53.10, writes: 23.60, response time: 2869.82ms (95%), errors: 0.00, reconnects: 0.00
...

At the moment of the shift from one node to another the applications will have to manage the RE-TRY, but it will be a very short moment that will cause limited impact on the production flow.

Application readers will see no errors:

[ 10s] threads: 10, tps: 0.00, reads: 13007.31, writes: 0.00, response time: 9.13ms (95%), errors: 0.00, reconnects: 0.00
[ 50s] threads: 10, tps: 0.00, reads: 9613.70, writes: 0.00, response time: 10.66ms (95%), errors: 0.00, reconnects: 0.20 <-- just a glitch in reconnect
[ 60s] threads: 10, tps: 0.00, reads: 10807.90, writes: 0.00, response time: 11.07ms (95%), errors: 0.00, reconnects: 0.20
[ 70s] threads: 10, tps: 0.00, reads: 9082.61, writes: 0.00, response time: 23.62ms (95%), errors: 0.00, reconnects: 0.00
...
[ 390s] threads: 10, tps: 0.00, reads: 13050.80, writes: 0.00, response time: 8.97ms (95%), errors: 0.00, reconnects: 0.00

When the Donor had end to provide SST it comes back and the script manage it, Glara_check will put it in the right HG:

2016/09/04 16:12:34.266:[WARN] Move node:192.168.1.5;3306;9500;1010 SQL: UPDATE mysql_servers SET hostgroup_id=500 WHERE hostgroup_id=9500 AND hostname='192.168.1.5' AND port='3306'
2016/09/04 16:12:34.270:[WARN] Move node:192.168.1.5;3306;9501;1010 SQL: UPDATE mysql_servers SET hostgroup_id=501 WHERE hostgroup_id=9501 AND hostname='192.168.1.5' AND port='3306'

The crashed node, will be re-start by the SST process, as such the node will be up.

But if the level of load in the cluster is mid/high it will remain in JOINED state for sometime, becoming visible by the ProxySQL again, while ProxySQL will not correctly recognize the state.

2016-09-04 16:17:15 21035 [Note] WSREP: 3.2 (node4): State transfer from 1.1 (node1) complete.2016-09-04 16:17:15 21035 [Note] WSREP: Shifting JOINER -> JOINED (TO: 254515)

To avoid issue the script will move it to special HG, allowing it to recovery without interfering with real load.

+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 6        | 2        | 15     | 0       | 3000    | 241060          | 0               | 141        |
| 500       | 192.168.1.6 | 3306     | ONLINE | 1        | 9        | 13     | 0       | 13128   | 1055268         | 0               | 84         |
| 500       | 192.168.1.7 | 3306     | ONLINE | 1        | 0        | 4      | 0       | 3756    | 301874          | 0               | 106        |
| 500       | 192.168.1.9 | 3306     | ONLINE | 1        | 0        | 2      | 0       | 4080    | 327872          | 0               | 278        |
| 501       | 192.168.1.5 | 3306     | ONLINE | 1        | 0        | 2      | 0       | 256753  | 12508935        | 772048259       | 141        |
| 501       | 192.168.1.6 | 3306     | ONLINE | 4        | 8        | 12     | 0       | 5116844 | 249191524       | 15100617833     | 84         |
| 501       | 192.168.1.7 | 3306     | ONLINE | 2        | 11       | 13     | 0       | 4739756 | 230863200       | 13997231724     | 106        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 496524  | 24214563        | 1496482104      | 278        |
| 9500      | 192.168.1.8 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 331        |<-- Joined not Sync
| 9501      | 192.168.1.8 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 331        |<-- Joined not Sync
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
Once Node fully recover, galera_check put it back IN the original HG, ready serve requests:
 
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 0        | 1        | 15     | 0       | 3444    | 276758          | 0               | 130        |
| 500       | 192.168.1.6 | 3306     | ONLINE | 0        | 9        | 13     | 0       | 13200   | 1061056         | 0               | 158        |
| 500       | 192.168.1.7 | 3306     | ONLINE | 0        | 0        | 4      | 0       | 3828    | 307662          | 0               | 139        |
| 500       | 192.168.1.8 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 0          |<-- up again
| 500       | 192.168.1.9 | 3306     | ONLINE | 0        | 0        | 2      | 0       | 4086    | 328355          | 0               | 336        |
| 501       | 192.168.1.5 | 3306     | ONLINE | 0        | 1        | 2      | 0       | 286349  | 13951366        | 861638962       | 130        |
| 501       | 192.168.1.6 | 3306     | ONLINE | 0        | 12       | 12     | 0       | 5239212 | 255148806       | 15460951262     | 158        |
| 501       | 192.168.1.7 | 3306     | ONLINE | 0        | 13       | 13     | 0       | 4849970 | 236234446       | 14323937975     | 139        |
| 501       | 192.168.1.8 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 0          |<-- up again
| 501       | 192.168.1.9 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 507910  | 24768898        | 1530841172      | 336        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

Summarizing the logical steps are:

                +---------+
                |  Crash  |
                +----+----+
                     |
                     v
            +--------+-------+
            |  ProxySQL      |
            |  shun crashed  |
            |      node      |
            +--------+-------+
                     |
                     |
                     v
   +-----------------+-----------------+
   |  Donor has one of the following?  |
   |  wsrep_sst_dono _rejects_queries  |
   |  OR                               |
   |  wsrep_reject_queries             |
   +-----------------------------------+
      |No                            |Yes
      v                              v
+-----+----------+       +-----------+----+
| Galera_check   |       | Galera_check   |
| put the donor  |       | put the donor  |
| in OFFLINE_SOFT|       | in special HG  |
+---+------------+       +-----------+----+
    |                                |
    |                                |
    v                                v
+---+--------------------------------+-----+
|            Donor SST ends                |
+---+---------------+----------------+-----+
    |               |                |
    |               |                |
+---+------------+  |    +-----------+----+
| Galera_check   |  |    | Galera_check   |
| put the donor  |  |    | put the donor  |
| ONLINE         |  |    | in Original HG |
+----------------+  |    +----------------+
                    |                
                    |                 
+------------------------------------------+
|           crashed SST ends               |
+-------------------+----------------------+
                    |
                    |
       +------------+-------------+
       |  Crashed node back but   +<------------+
       |  Not Sync?               |             |
       +--------------------------+             |
          |No                   |Yes            |
          |                     |               |
          |                     |               |
+---------+------+       +------+---------+     |
| Galera_check   |       | Galera_check   |     |
| put the node   |       | put the node   +-----+
| back orig. HG  |       | Special HG     |
+--------+-------+       +----------------+
         |
         |
         |
         |      +---------+
         +------>   END   |
                +---------+

As mention in this integration with galera_check we can manage several node states.

Another case is when we need to have the node not accepting ANY query.

We may need that for several reasons, including preparing the node for maintenance or whatever.

In PXC and other Galera implementation we can set the value of wsrep_reject_queries to:

Valid Values
NONE

ALL

ALL_KILL

Let see how it works:

run some load then on the main writer node (192.168.1.5)

SET global wsrep_reject_queries=ALL;

This will block any new queries to be executed while the running will be completed.

Do a simple select on the node :

(root@localhost:pm) [test]>select * FROM tbtest1;
ERROR 1047 (08S01): WSREP has NOT yet prepared node FOR application USE

Point is , as you should have understand by now, that ProxySQL do not see these conditions:

+-------------+------+------------------+----------------------+------------+
| hostname    | port | time_start_us    | ping_success_time_us | ping_error |
+-------------+------+------------------+----------------------+------------+
| 192.168.1.5 | 3306 | 1473005467628001 | 35                   | NULL       | <--- ping ok
| 192.168.1.5 | 3306 | 1473005437628014 | 154                  | NULL       |
+-------------+------+------------------+----------------------+------------+
+-------------+------+------------------+-------------------------+---------------+
| hostname    | port | time_start_us    | connect_success_time_us | connect_error |
+-------------+------+------------------+-------------------------+---------------+
| 192.168.1.5 | 3306 | 1473005467369575 | 246                     | NULL          | <--- connect ok
| 192.168.1.5 | 3306 | 1473005407369441 | 353                     | NULL          |
+-------------+------+------------------+-------------------------+---------------+

The script Galera check will instead manage it:

+-----------+-------------+----------+--------------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS       | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | OFFLINE_SOFT | 0        | 0        | 8343   | 0       | 10821   | 240870          | 0               | 93         | <--- galera check put it OFFLINE
| 500       | 192.168.1.6 | 3306     | ONLINE       | 10       | 0        | 15     | 0       | 48012   | 3859402         | 0               | 38         | <--- writer
| 500       | 192.168.1.7 | 3306     | ONLINE       | 0        | 1        | 6      | 0       | 14712   | 1182364         | 0               | 54         |
| 500       | 192.168.1.8 | 3306     | ONLINE       | 0        | 1        | 2      | 0       | 1092    | 87758           | 0               | 602        |
| 500       | 192.168.1.9 | 3306     | ONLINE       | 0        | 1        | 4      | 0       | 5352    | 430152          | 0               | 238        |
| 501       | 192.168.1.5 | 3306     | OFFLINE_SOFT | 0        | 0        | 1410   | 0       | 197909  | 9638665         | 597013919       | 93         |
| 501       | 192.168.1.6 | 3306     | ONLINE       | 2        | 10       | 12     | 0       | 7822682 | 380980455       | 23208091727     | 38         |
| 501       | 192.168.1.7 | 3306     | ONLINE       | 0        | 13       | 13     | 0       | 7267507 | 353962618       | 21577881545     | 54         |
| 501       | 192.168.1.8 | 3306     | ONLINE       | 0        | 1        | 1      | 0       | 241641  | 11779770        | 738145270       | 602        |
| 501       | 192.168.1.9 | 3306     | ONLINE       | 1        | 0        | 1      | 0       | 756415  | 36880233        | 2290165636      | 238        |
+-----------+-------------+----------+--------------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

In this case the script will put the node in OFFLINE_SOFT, given the "set global wsrep_reject_queries=ALL" means do not accept NEW complete the existing, as OFFLINE_SOFT.

The script manage also in the case of "set global wsrep_reject_queries=ALL_KILL;" .

Which from ProxySQL point of view do not exists as well:

+-------------+------+------------------+----------------------+------------+
| hostname    | port | time_start_us    | ping_success_time_us | ping_error |
+-------------+------+------------------+----------------------+------------+
| 192.168.1.5 | 3306 | 1473005827629069 | 59                   | NULL       |<--- ping ok
| 192.168.1.5 | 3306 | 1473005797628988 | 57                   | NULL       |
+-------------+------+------------------+----------------------+------------+
+-------------+------+------------------+-------------------------+---------------+
| hostname    | port | time_start_us    | connect_success_time_us | connect_error |
+-------------+------+------------------+-------------------------+---------------+
| 192.168.1.5 | 3306 | 1473005827370084 | 370                     | NULL          | <--- connect ok
| 192.168.1.5 | 3306 | 1473005767369915 | 243                     | NULL          |
+-------------+------+------------------+-------------------------+---------------+
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 9500      | 192.168.1.5 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 0          |<--- galera check put it in special HG
| 9501      | 192.168.1.5 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0       | 0               | 0               | 0          |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

The difference here is that the script moves the node to the special HG to isolate it, instead let it be in the original HG.

As you can see the integration between ProxySQL and PXC(galera) in the case of multi-writer, works perfectly, if you have a script as galera_check that manage correctly the different PXC/Galera states.

ProxySQL and PXC using Replication HostGroup

Sometimes we may need to have the 100% of the write going to one node only a time.

As explain above ProxySQL use weight to redirect a % of the load to a specific node.

In most of the case it will be enough to set the weight in the main writer to a very high value, like 10 billions and on the next node to 1 thousands, to achieve an almost single writer.

But this is not 100%, it still allow ProxySQL to send a query once every X to the other node(s).

The solution to this and to keep it consistent with the ProxySQL logic, is to use replication Hostgroups.

Replication HG are special HG that Proxy see as connected for R/W operations.

ProxySQL analyze the value of the READ_ONLY variables and assign to the READ_ONLY HG the nodes that have it enable.

While the node having READ_ONLY=0, reside in both HG.

As such the first thing we need to modify is to say to ProxySQL that our two HG 500 and 501 are replication HG.

INSERT INTO mysql_replication_hostgroups VALUES (500,501,'');
LOAD MYSQL SERVERS TO RUNTIME; SAVE MYSQL SERVERS TO DISK; 
SELECT * FROM mysql_replication_hostgroups ;
+------------------+------------------+---------+
| writer_hostgroup | reader_hostgroup | comment |
+------------------+------------------+---------+
| 500              | 501              |         |
+------------------+------------------+---------+

Now whenever I will set the value of READ_ONLY on a node ProxySQL will move the node accordingly.

Let see how.

Current:

+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 6        | 1        | 7      | 0       | 16386    | 1317177         | 0               | 97         |
| 500       | 192.168.1.6 | 3306     | ONLINE | 1        | 9        | 15     | 0       | 73764    | 5929366         | 0               | 181        |
| 500       | 192.168.1.7 | 3306     | ONLINE | 1        | 0        | 6      | 0       | 18012    | 1447598         | 0               | 64         |
| 500       | 192.168.1.8 | 3306     | ONLINE | 1        | 0        | 2      | 0       | 1440     | 115728          | 0               | 341        |
| 501       | 192.168.1.5 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 1210029  | 58927817        | 3706882671      | 97         |
| 501       | 192.168.1.6 | 3306     | ONLINE | 1        | 11       | 12     | 0       | 16390790 | 798382865       | 49037691590     | 181        |
| 501       | 192.168.1.7 | 3306     | ONLINE | 1        | 12       | 13     | 0       | 15357779 | 748038558       | 45950863867     | 64         |
| 501       | 192.168.1.8 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 1247662  | 60752227        | 3808131279      | 341        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 1766309  | 86046839        | 5374169120      | 422        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+

Set global READ_ONLY=1;

on the following nodes 192.168.1.6/7/8/9

After:

+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 10       | 0        | 20     | 0       | 25980    | 2088346         | 0               | 93         |
| 501       | 192.168.1.5 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 1787979  | 87010074        | 5473781192      | 93         |
| 501       | 192.168.1.6 | 3306     | ONLINE | 4        | 8        | 12     | 0       | 18815907 | 916547402       | 56379724890     | 79         |
| 501       | 192.168.1.7 | 3306     | ONLINE | 1        | 12       | 13     | 0       | 17580636 | 856336023       | 52670114510     | 131        |
| 501       | 192.168.1.8 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 15324    | 746109          | 46760779        | 822        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 16210    | 789999          | 49940867        | 679        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+

In this scenario, IF a reader node crash, the application will not suffer at all given the redundancy.

But if the writer is going to crash THEN the issue exists, because there will be NO node available to manage the failover.

The solution is either do the node election manually, or to have the script elect the node with the lowest read weight in the same segment as new writer.

The one below is what is going to happen when a node crash (bird-eye view):

                         +---------+
                         |  Crash  |
                         +----+----+
                              |
                              v
                     +--------+-------+
                     |  ProxySQL      |
                     |  shun crashed  |
                     |      node      |
                     +--------+-------+
                              |
                              |
                              v
            +-----------------+-----------------+
+----------->   HostGroup has another active    |
|           |   Node in HG writer?              |
|           +--+--------------+---------------+-+
|              |              |               |
|              |              |               |
|              |No            |               |Yes
|              |              |               |
|        +-----v----------+   |   +-----------v----+
|        |ProxySQL will   |   |   |ProxySQL will   |
|        |stop serving    |   |   |redirect load   >--------+
|        |writes          |   |   |there           |        |
|        +----------------+   |   +----------------+        |
|                             |                             |
|                             v                             |
|                     +-------+--------+                    |
|                     |ProxySQL checks |                    |
|                     |READ_ONLY on    |                    |
|                     |Reader HG       |                    |
|                     |                |                    |
|                     +-------+--------+                    |
|                             |                             |
|                             v                             |
|                     +-------+--------+                    |
|                     |Any Node with   |                    |
|                     |READ_ONLY = 0 ? |                    |
|                     +----------------+                    |
|                      |No            |Yes                  |
|                      |              |                     |
|           +----------v------+    +--v--------------+      |
|           |ProxySQL will    |    |ProxySQL will    |      |
|           |continue to      |    |Move node to     |      |
+<---------<+do not serve     |    |Writer HG        |      |
|           |Writes           |    |                 |      |
|           +-----------------+    +--------v--------+      |
|                                           |               |
+-------------------------------------------+               |
                         +---------+                        |
                         |   END   <------------------------+
                         +---------+

The script should act in the step immediately after ProxySQL SHUNNED the node, just replacing the READ_ONLY=1 with READ_ONLY=0, on the reader node with the lowest READ WEIGHT.

ProxySQL will do the rest, copying the Node into the WRITER HG, keeping low weight, such that WHEN/IF the original node will comeback, the new node will not compete for traffic.

I had included that special function in the check, the feature will allow automatic fail-over.

This experimental feature is active only if explicitly set in the parameter that the scheduler will pass to the script.

To activate it just add --active_failover list of arguments that is pass over the script in the scheduler.

My recommendation is to have two entries in the scheduler and activate the one with --active_failover for test, remember to deactivate the other.

Let see the manual procedure first

Process will be:

1 Generate some load

2 Kill the writer node

3 Manually elect a reader as writer

4 Recover crashed node

Current load:

+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 10       | 0        | 10     | 0       | 30324   | 2437438         | 0               | 153        |
| 501       | 192.168.1.5 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 1519612 | 74006447        | 4734427711      | 153        |
| 501       | 192.168.1.6 | 3306     | ONLINE | 4        | 8        | 12     | 0       | 7730857 | 376505014       | 24119645457     | 156        |
| 501       | 192.168.1.7 | 3306     | ONLINE | 2        | 10       | 12     | 0       | 7038332 | 342888697       | 21985442619     | 178        |
| 501       | 192.168.1.8 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 612523  | 29835858        | 1903693835      | 337        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 611021  | 29769497        | 1903180139      | 366        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

Kill the main node 192.168.1.5

+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS  | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 501       | 192.168.1.5 | 3306     | SHUNNED | 0        | 0        | 1      | 11      | 1565987 | 76267703        | 4879938857      | 119        |
| 501       | 192.168.1.6 | 3306     | ONLINE  | 1        | 11       | 12     | 0       | 8023216 | 390742215       | 25033271548     | 112        |
| 501       | 192.168.1.7 | 3306     | ONLINE  | 1        | 11       | 12     | 0       | 7306838 | 355968373       | 22827016386     | 135        |
| 501       | 192.168.1.8 | 3306     | ONLINE  | 1        | 0        | 1      | 0       | 638326  | 31096065        | 1984732176      | 410        |
| 501       | 192.168.1.9 | 3306     | ONLINE  | 1        | 0        | 1      | 0       | 636857  | 31025014        | 1982213114      | 328        |
+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
+-------------+------+------------------+----------------------+------------------------------------------------------+
| hostname    | port | time_start_us    | ping_success_time_us | ping_error                                           |
+-------------+------+------------------+----------------------+------------------------------------------------------+
| 192.168.1.5 | 3306 | 1473070640798571 | 0                    | Can't connect to MySQL server on '192.168.1.5' (107) |
| 192.168.1.5 | 3306 | 1473070610798464 | 0                    | Can't connect TO MySQL server ON '192.168.1.5' (107) |
+-------------+------+------------------+----------------------+------------------------------------------------------+
+-------------+------+------------------+-------------------------+------------------------------------------------------+
| hostname    | port | time_start_us    | connect_success_time_us | connect_error                                        |
+-------------+------+------------------+-------------------------+------------------------------------------------------+
| 192.168.1.5 | 3306 | 1473070640779903 | 0                       | Can't connect to MySQL server on '192.168.1.5' (107) |
| 192.168.1.5 | 3306 | 1473070580779977 | 0                       | Can't connect TO MySQL server ON '192.168.1.5' (107) |
+-------------+------+------------------+-------------------------+------------------------------------------------------+

When the node is killed ProxySQL Shun it and also report issues with the checks (connect and ping)

During this time frame the Application will experience issues, and if is not designed to manage the retry, and eventually a queue, it will crash.

Sysbench report the errors:

Writes
 
[  10s] threads: 10, tps: 6.70, reads: 68.50, writes: 30.00, response time: 1950.53ms (95%), errors: 0.00, reconnects:  0.00
...
[1090s] threads: 10, tps: 4.10, reads: 36.90, writes: 16.40, response time: 2226.45ms (95%), errors: 0.00, reconnects:  1.00  <-+ killing the node
[1100s] threads: 10, tps: 0.00, reads: 0.00, writes: 0.00, response time: 0.00ms (95%), errors: 1.00, reconnects:  0.00         |
[1110s] threads: 10, tps: 0.00, reads: 0.00, writes: 0.00, response time: 0.00ms (95%), errors: 1.00, reconnects:  0.00         |
[1120s] threads: 10, tps: 0.00, reads: 0.00, writes: 0.00, response time: 0.00ms (95%), errors: 1.00, reconnects:  0.00         |
[1130s] threads: 10, tps: 0.00, reads: 0.00, writes: 0.00, response time: 0.00ms (95%), errors: 1.00, reconnects:  0.00         |-- Gap waiting for a node to become
[1140s] threads: 10, tps: 0.00, reads: 0.00, writes: 0.00, response time: 0.00ms (95%), errors: 1.00, reconnects:  0.00         |   READ_ONLY=0
[1150s] threads: 10, tps: 0.00, reads: 0.00, writes: 0.00, response time: 0.00ms (95%), errors: 1.00, reconnects:  0.00         |
[1160s] threads: 10, tps: 0.00, reads: 0.00, writes: 0.00, response time: 0.00ms (95%), errors: 1.00, reconnects:  0.00         |
[1170s] threads: 10, tps: 4.70, reads: 51.30, writes: 22.80, response time: 80430.18ms (95%), errors: 0.00, reconnects:  0.00 <-+
[1180s] threads: 10, tps: 8.90, reads: 80.10, writes: 35.60, response time: 2068.39ms (95%), errors: 0.00, reconnects:  0.00
...
 [1750s] threads: 10, tps: 5.50, reads: 49.80, writes: 22.80, response time: 2266.80ms (95%), errors: 0.00, reconnects:  0.00 -- No additional errors

I decided to promote node 192.168.1.6 given in this setup the weight for readers was equal and as such no difference.

(root@localhost:pm) [(none)]>set global read_only=0;
Query OK, 0 rows affected (0.00 sec)

Checking proxySQL:

+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS  | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.1.6 | 3306     | ONLINE  | 10       | 0        | 10     | 0       | 1848    | 148532          | 0               | 40         |
| 501       | 192.168.1.5 | 3306     | SHUNNED | 0        | 0        | 1      | 72      | 1565987 | 76267703        | 4879938857      | 38         |
| 501       | 192.168.1.6 | 3306     | ONLINE  | 2        | 10       | 12     | 0       | 8843069 | 430654903       | 27597990684     | 40         |
| 501       | 192.168.1.7 | 3306     | ONLINE  | 1        | 11       | 12     | 0       | 8048826 | 392101994       | 25145582384     | 83         |
| 501       | 192.168.1.8 | 3306     | ONLINE  | 1        | 0        | 1      | 0       | 725820  | 35371512        | 2259974847      | 227        |
| 501       | 192.168.1.9 | 3306     | ONLINE  | 1        | 0        | 1      | 0       | 723582  | 35265066        | 2254824754      | 290        |
+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

As the READ_ONLY value is modified, ProxySQL move it to the writer Hostgroup and writes can take place again.

At this point in time production activities are recovered.

Reads had just a minor glitch:

Reads
[  10s] threads: 10, tps: 0.00, reads: 20192.15, writes: 0.00, response time: 6.96ms (95%), errors: 0.00, reconnects:  0.00
...
[ 410s] threads: 10, tps: 0.00, reads: 16489.03, writes: 0.00, response time: 9.41ms (95%), errors: 0.00, reconnects:  2.50
...
[ 710s] threads: 10, tps: 0.00, reads: 18789.40, writes: 0.00, response time: 6.61ms (95%), errors: 0.00, reconnects:  0.00

when node 192.168.1.6 was copied over to HG 500, but no interruptions or errors.

At this point let us put back the crashed node, which coming back elect Node2 (192.168.1.6) as donor.

This was a PXC/Galera choice and we have to accept and manage it.

Note that the other basic scripts ( will put the node in OFFLINE_SOFT, given the node will become a DONOR).

Galera_check will recognize that Node2 (192.168.1.6) is the only active node in the segment for that specific HG (writer), while is not the only present for the READER HG.

As such it will put the node in OFFLINE_SOFT only for the READER HG, trying to reduce load on the node, but it will keep it active in the WRITER HG, to prevent service interruption.

Node restart and ask for a donor:

2016-09-05 12:21:43 8007 [Note] WSREP: Flow-control interval: [67, 67]
2016-09-05 12:21:45 8007 [Note] WSREP: Member 1.1 (node1) requested state transfer from '*any*'. Selected 0.1 (node2)(SYNCED) as donor.
2016-09-05 12:21:46 8007 [Note] WSREP: (ef248c1f, 'tcp://192.168.1.8:4567') turning message relay requesting off
2016-09-05 12:21:52 8007 [Note] WSREP: New cluster view: global state: 234bb6ed-527d-11e6-9971-e794f632b140:324329, view# 7: Primary, number of nodes: 5, my index: 3, protocol version 3

Galera_check will set OFFLINE_SOFT 192.168.1.6 only for the READER HG, and ProxySQL will use the others to serve reads.

+-----------+-------------+----------+--------------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS       | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.6 | 3306     | ONLINE       | 10       | 0        | 10     | 0       | 7746     | 622557          | 0               | 86         |
| 501       | 192.168.1.5 | 3306     | ONLINE       | 0        | 0        | 1      | 147     | 1565987  | 76267703        | 4879938857      | 38         |
| 501       | 192.168.1.6 | 3306     | OFFLINE_SOFT | 0        | 0        | 12     | 0       | 9668944  | 470878452       | 30181474498     | 86         | <-- Node offline
| 501       | 192.168.1.7 | 3306     | ONLINE       | 9        | 3        | 12     | 0       | 10932794 | 532558667       | 34170366564     | 62         |
| 501       | 192.168.1.8 | 3306     | ONLINE       | 0        | 1        | 1      | 0       | 816599   | 39804966        | 2545765089      | 229        |
| 501       | 192.168.1.9 | 3306     | ONLINE       | 0        | 1        | 1      | 0       | 814893   | 39724481        | 2541760230      | 248        |
+-----------+-------------+----------+--------------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+

When SST donor task is over and Galera_check moves the 192.168.1.6 back ONLINE as expected.

But at the same time, it moves the recovering node to the special HG to avoid to have it included in any activity until ready.

2016-09-05 12:22:36 27352 [Note] WSREP: 1.1 (node1): State transfer FROM 0.1 (node2) complete.
2016-09-05 12:22:36 27352 [Note] WSREP: Shifting JOINER -> JOINED (TO: 325062)
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.6 | 3306     | ONLINE | 10       | 0        | 10     | 0       | 1554     | 124909          | 0               | 35         |
| 501       | 192.168.1.6 | 3306     | ONLINE | 2        | 8        | 22     | 0       | 10341612 | 503637989       | 32286072739     | 35         |
| 501       | 192.168.1.7 | 3306     | ONLINE | 3        | 9        | 12     | 0       | 12058701 | 587388598       | 37696717375     | 13         |
| 501       | 192.168.1.8 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 890102   | 43389051        | 2776691164      | 355        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 887994   | 43296865        | 2772702537      | 250        |
| 9500      | 192.168.1.5 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 57         | <-- Special HG for recover
| 9501      | 192.168.1.5 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 57         | <-- Special HG for recover
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+

Once finally the node is in SYNC with the group it is put back online in the READER HG and in the writer HG:

2016-09-05 12:22:36 27352 [Note] WSREP: 1.1 (node1): State transfer FROM 0.1 (node2) complete.
2016-09-05 12:22:36 27352 [Note] WSREP: Shifting JOINER -> JOINED (TO: 325062)
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries  | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0        | 0               | 0               | 0          | <-- Back on line
| 500       | 192.168.1.6 | 3306     | ONLINE | 10       | 0        | 10     | 0       | 402      | 32317           | 0               | 68         |
| 501       | 192.168.1.5 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 6285     | 305823          | 19592814        | 312        | <-- Back on line
| 501       | 192.168.1.6 | 3306     | ONLINE | 4        | 6        | 22     | 0       | 10818694 | 526870710       | 33779586475     | 68         |
| 501       | 192.168.1.7 | 3306     | ONLINE | 0        | 12       | 12     | 0       | 12492316 | 608504039       | 39056093665     | 26         |
| 501       | 192.168.1.8 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 942023   | 45924082        | 2940228050      | 617        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 939975   | 45834039        | 2935816783      | 309        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+----------+-----------------+-----------------+------------+
+--------------+-------------+------+--------+------------+
| hostgroup_id | hostname    | port | STATUS | weight     |
+--------------+-------------+------+--------+------------+
| 500          | 192.168.1.5 | 3306 | ONLINE | 100        |
| 500          | 192.168.1.6 | 3306 | ONLINE | 1000000000 |
| 501          | 192.168.1.5 | 3306 | ONLINE | 100        |
| 501          | 192.168.1.6 | 3306 | ONLINE | 1000000000 |
| 501          | 192.168.1.7 | 3306 | ONLINE | 1000000000 |
| 501          | 192.168.1.8 | 3306 | ONLINE | 1          |
| 501          | 192.168.1.9 | 3306 | ONLINE | 1          |
+--------------+-------------+------+--------+------------+

But given is coming back with its READER WEIGHT, it will NOT compete with the previously elected WRITER.

The recovered node will stay on "hold" waiting for a DBA to act and eventually put it back, or be set as READ_ONLY and as such be fully removed from the WRITER HG.

Let see the Automatic procedure now

As such let for the moment just stay stick to the MANUAL failover process.

Process will be:

1 Generate some load

2 Kill the writer node

3 Script will do auto-failover

4 Recover crashed node

Check our scheduler config:

+----+--------+-------------+-----------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------+------+------+------+---------+
| id | active | interval_ms | filename | arg1 | arg2 | arg3 | arg4 | arg5 | comment |
+----+--------+-------------+-----------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------+------+------+------+---------+
| 10 | 1 | 2000 | /var/lib/proxysql/galera_check.pl | -u=admin -p=admin -h=192.168.1.50 -H=500:W,501:R -P=3310 --execution_time=1 --retry_down=2 --retry_up=1 --main_segment=1 --active_failover --debug=0 --log=/var/lib/proxysql/galeraLog | NULL | NULL | NULL | NULL | | <--- Active
| 20 | 0 | 1500 | /var/lib/proxysql/galera_check.pl | -u=admin -p=admin -h=192.168.1.50 -H=500:W,501:R -P=3310 --execution_time=1 --retry_down=2 --retry_up=1 --main_segment=1 --debug=0 --log=/var/lib/proxysql/galeraLog | NULL | NULL | NULL | NULL | |
+----+--------+-------------+-----------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------+------+------+------+---------+

Active is the one with auto-failover

Start load and check Current load:

+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.1.5 | 3306     | ONLINE | 10       | 0        | 10     | 0       | 952     | 76461           | 0               | 0          |
| 501       | 192.168.1.5 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 53137   | 2587784         | 165811100       | 167        |
| 501       | 192.168.1.6 | 3306     | ONLINE | 5        | 5        | 11     | 0       | 283496  | 13815077        | 891230826       | 109        |
| 501       | 192.168.1.7 | 3306     | ONLINE | 3        | 7        | 10     | 0       | 503516  | 24519457        | 1576198138      | 151        |
| 501       | 192.168.1.8 | 3306     | ONLINE | 1        | 0        | 1      | 0       | 21952   | 1068972         | 68554796        | 300        |
| 501       | 192.168.1.9 | 3306     | ONLINE | 0        | 1        | 1      | 0       | 21314   | 1038593         | 67043935        | 289        |
+-----------+-------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

Kill the main node 192.168.1.5

+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host    | srv_port | STATUS  | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 500       | 192.168.1.6 | 3306     | ONLINE  | 10       | 0        | 10     | 0       | 60      | 4826            | 0               | 0          |
| 501       | 192.168.1.5 | 3306     | SHUNNED | 0        | 0        | 1      | 11      | 177099  | 8626778         | 552221651       | 30         |
| 501       | 192.168.1.6 | 3306     | ONLINE  | 3        | 7        | 11     | 0       | 956724  | 46601110        | 3002941482      | 49         |
| 501       | 192.168.1.7 | 3306     | ONLINE  | 2        | 8        | 10     | 0       | 1115685 | 54342756        | 3497575125      | 42         |
| 501       | 192.168.1.8 | 3306     | ONLINE  | 0        | 1        | 1      | 0       | 76289   | 3721419         | 240157393       | 308        |
| 501       | 192.168.1.9 | 3306     | ONLINE  | 1        | 0        | 1      | 0       | 75803   | 3686067         | 236382784       | 231        |
+-----------+-------------+----------+---------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

When the node is killed the node is SHUNNED, but this time the script had already set the new node 192.168.1.6 ONLINE

See script log

2016/09/08 14:04:02.494:[INFO] END EXECUTION Total Time:102.347850799561
2016/09/08 14:04:04.478:[INFO] This Node Try to become a WRITER set READ_ONLY to 0 192.168.1.6:3306:HG501
2016/09/08 14:04:04.479:[INFO] This Node NOW HAS READ_ONLY = 0 192.168.1.6:3306:HG501
2016/09/08 14:04:04.479:[INFO] END EXECUTION Total Time:71.8140602111816

More important the application experience

Writes
 
[  10s] threads: 10, tps: 9.40, reads: 93.60, writes: 41.60, response time: 1317.41ms (95%), errors: 0.00, reconnects:  0.00
[  20s] threads: 10, tps: 8.30, reads: 74.70, writes: 33.20, response time: 1350.96ms (95%), errors: 0.00, reconnects:  0.00
[  30s] threads: 10, tps: 8.30, reads: 74.70, writes: 33.20, response time: 1317.81ms (95%), errors: 0.00, reconnects:  0.00
[  40s] threads: 10, tps: 7.80, reads: 70.20, writes: 31.20, response time: 1407.51ms (95%), errors: 0.00, reconnects:  0.00
[  50s] threads: 10, tps: 6.70, reads: 60.30, writes: 26.80, response time: 2259.35ms (95%), errors: 0.00, reconnects:  0.00
[  60s] threads: 10, tps: 6.60, reads: 59.40, writes: 26.40, response time: 3275.78ms (95%), errors: 0.00, reconnects:  0.00
[  70s] threads: 10, tps: 5.70, reads: 60.30, writes: 26.80, response time: 1492.56ms (95%), errors: 0.00, reconnects:  1.00 <-- just a reconnect experience
[  80s] threads: 10, tps: 6.70, reads: 60.30, writes: 26.80, response time: 7959.74ms (95%), errors: 0.00, reconnects:  0.00
[  90s] threads: 10, tps: 6.60, reads: 59.40, writes: 26.40, response time: 2109.03ms (95%), errors: 0.00, reconnects:  0.00
[ 100s] threads: 10, tps: 6.40, reads: 57.60, writes: 25.60, response time: 1883.96ms (95%), errors: 0.00, reconnects:  0.00
[ 110s] threads: 10, tps: 5.60, reads: 50.40, writes: 22.40, response time: 2167.27ms (95%), errors: 0.00, reconnects:  0.00

No errors no huge delay, our application (managing reconnect) had only glitch, and had to reconnect.

Read had no errors or reconnects.

The connection errors were managed by ProxySQL and given it found 5 in 1sec it SHUNNED the node.

The galera_script was able to promote a reader, and given it is a failover no delay with retry loop.

The whole thing is done in such brief time that application barely see it.

Obviously an application with thousands of connections/sec will experience more impact, but the time-window will be very narrow, and that was our scope.

Once the failed node is ready to come back, either we choose to start it with READ_ONLY=1, as such it will come back as reader.

Or we will keep it as it is and it will come back as writer.

No matter what the script will manage the case as it had done in the previous (manual) exercise.

Conclusions

As shown ProxySQL and galera_check working together are quite efficient in managing the cluster and its different scenario.

When using the Single-Writer mode, solving the manual part of the failover dramatically improve the efficiency in performing the recovery of the production state, going from few minutes to seconds or less.

The Multiwriter mode remain the preferred and most recommended way to use ProxySQL/PXC given it will perform failover without the need of additional scripts or extension, also if a script is still required to manage the integration with ProxySQL.

In both cases the use of a script able to identify the multiple state of PXC and the mutable node scenario, is a crucial part of the implementation without which ProxySQL may not behave correctly.

ProxySQL and MHA integration

ProxySQL and MHA integration
MHA (Master High Availability Manager and tools for MySQL), is almost fully integrated with the ProxySQL process.

What it means is that you can count on the MHA standard feature to manage the failover, and on ProxySQL to manage the traffic and shift from one server.

This is one of the main difference between using MHA and VIP vs MHA and ProxySQL.

There is no need to move IPs or re-define DNS.

The following is an example of configuration file for MHA in case you use it with ProxySQL:

[server default]
    user=mha
    password=mha
    ssh_user=root
    repl_password=replica
    manager_log=/tmp/mha.log
    manager_workdir=/tmp
    remote_workdir=/tmp
    master_binlog_dir=/opt/mysql_instances/mha1/logs
    client_bindir=/opt/mysql_templates/mysql-57/bin
    client_libdir=/opt/mysql_templates/mysql-57/lib
    master_ip_failover_script=/opt/tools/mha/mha4mysql-manager/samples/scripts/master_ip_failover
    master_ip_online_change_script=/opt/tools/mha/mha4mysql-manager/samples/scripts/master_ip_online_change
    log_level=debug
 
    [server1]
    hostname=mha1r
    ip=192.168.1.104
    candidate_master=1
 
    [server2]
    hostname=mha2r
    ip=192.168.1.107
    candidate_master=1
 
    [server3]
    hostname=mha3r
    ip=192.168.1.111
    candidate_master=1
 
    [server4]
    hostname=mha4r
    ip=192.168.1.109
    no_master=1

The only thing you need to be sure is to comment out the "FIX ME " lines in the sample/scripts.

In the MHA installation direcotry look for :

mha4mysql-manager/samples/scripts/master_ip_failover

mha4mysql-manager/samples/scripts/master_ip_online_change

After that just install MHA as you are used to.
In ProxySQL be sure to have mha users and the servers set.

One very important thing when using ProxySQL with standard replication is that we need to set additional privileges to the ProxySQL monitor user.
It must have "Replication Client" set or it will fail to check the SLAVE LAG.

Also the Servers MUST have a defined value for the attribute max_replication_lag, or the check will be ignore.

As a reminder:

INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.104',600,3306,1000,0);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.104',601,3306,1000,10);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.107',601,3306,1000,10);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.111',601,3306,1000,10);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight,max_replication_lag) VALUES ('192.168.1.109',601,3306,1000,10);
INSERT INTO mysql_replication_hostgroups VALUES (600,601);
LOAD MYSQL SERVERS TO RUNTIME; SAVE MYSQL SERVERS TO DISK;
INSERT INTO mysql_query_rules (username,destination_hostgroup,active) VALUES('mha_W',600,1);
INSERT INTO mysql_query_rules (username,destination_hostgroup,active) VALUES('mha_R',601,1);
INSERT INTO mysql_query_rules (username,destination_hostgroup,active,retries,match_digest) VALUES('mha_RW',600,1,3,'^SELECT.*FOR UPDATE');
INSERT INTO mysql_query_rules (username,destination_hostgroup,active,retries,match_digest) VALUES('mha_RW',601,1,3,'^SELECT');
LOAD MYSQL QUERY RULES TO RUNTIME;SAVE MYSQL QUERY RULES TO DISK;
INSERT INTO mysql_users (username,password,active,default_hostgroup,default_schema,transaction_persistent) VALUES ('mha_W','test',1,600,'test_mha',1);
INSERT INTO mysql_users (username,password,active,default_hostgroup,default_schema,transaction_persistent) VALUES ('mha_R','test',1,601,'test_mha',1);
INSERT INTO mysql_users (username,password,active,default_hostgroup,default_schema,transaction_persistent) VALUES ('mha_RW','test',1,600,'test_mha',1);
LOAD MYSQL USERS TO RUNTIME;SAVE MYSQL USERS TO DISK

Ok all is ready let us rock'n'roll.

Controlled fail-over.First of all the masterha_manager should not be running or you will get error.

Then let us start some traffic.

Write
sysbench --test=/usr/share/doc/sysbench/tests/db/oltp.lua --mysql-host=192.168.1.50 --mysql-port=3311 --mysql-user=mha_RW --mysql-password=test --mysql-db=mha_test --db-driver=mysql --oltp-tables-count=50 --oltp-tablesize=5000 --max-requests=0 --max-time=900 --oltp-point-selects=5 --oltp-read-only=off --oltp-dist-type=uniform --oltp-reconnect-mode=transaction --oltp-skip-trx=off --num-threads=10 --report-interval=10 --mysql-ignore-errors=all  run
Read only
sysbench --test=/usr/share/doc/sysbench/tests/db/oltp.lua --mysql-host=192.168.1.50 --mysql-port=3311 --mysql-user=mha_RW --mysql-password=test --mysql-db=mha_test --db-driver=mysql --oltp-tables-count=50 --oltp-tablesize=5000 --max-requests=0 --max-time=900 --oltp-point-selects=5 --oltp-read-only=on --num-threads=10 --oltp-reconnect-mode=query --oltp-skip-trx=on --report-interval=10  --mysql-ignore-errors=all run

Let it run for a bit then check:

mysql> SELECT * FROM stats_mysql_connection_pool WHERE hostgroup BETWEEN 600 AND 601 ORDER BY hostgroup,srv_host DESC;
+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host      | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 600       | 192.168.1.104 | 3306     | ONLINE | 10       | 0        | 20     | 0       | 551256  | 44307633        | 0               | 285        | <--- current Master
| 601       | 192.168.1.111 | 3306     | ONLINE | 5        | 3        | 11     | 0       | 1053685 | 52798199        | 4245883580      | 1133       |
| 601       | 192.168.1.109 | 3306     | ONLINE | 3        | 5        | 10     | 0       | 1006880 | 50473746        | 4052079567      | 369        |
| 601       | 192.168.1.107 | 3306     | ONLINE | 3        | 5        | 13     | 0       | 1040524 | 52102581        | 4178965796      | 604        |
| 601       | 192.168.1.104 | 3306     | ONLINE | 7        | 1        | 16     | 0       | 987548  | 49458526        | 3954722258      | 285        |
+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

And now let us try to perform the failover.
To do we will instruct MHA to do a switch, and to set the OLD master as new slave:

masterha_master_switch --master_state=alive --conf=/etc/mha.cnf --orig_master_is_new_slave --interactive=0 --running_updates_limit=0

Now let us check what happened:

[ 160s] threads: 10, tps: 354.50, reads: 3191.10, writes: 1418.50, response time: 48.96ms (95%), errors: 0.00, reconnects:  0.00
[ 170s] threads: 10, tps: 322.50, reads: 2901.98, writes: 1289.89, response time: 55.45ms (95%), errors: 0.00, reconnects:  0.00
[ 180s] threads: 10, tps: 304.60, reads: 2743.12, writes: 1219.91, response time: 58.09ms (95%), errors: 0.10, reconnects:  0.00 <--- moment of the switch
[ 190s] threads: 10, tps: 330.40, reads: 2973.40, writes: 1321.00, response time: 50.52ms (95%), errors: 0.00, reconnects:  0.00
[ 200s] threads: 10, tps: 304.20, reads: 2745.60, writes: 1217.60, response time: 58.40ms (95%), errors: 0.00, reconnects:  1.00
[ 210s] threads: 10, tps: 353.80, reads: 3183.80, writes: 1414.40, response time: 48.15ms (95%), errors: 0.00, reconnects:  0.00

Check ProxySQL :

mysql> SELECT * FROM stats_mysql_connection_pool WHERE hostgroup BETWEEN 600 AND 601 ORDER BY hostgroup,srv_host DESC;
+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| hostgroup | srv_host      | srv_port | STATUS | ConnUsed | ConnFree | ConnOK | ConnERR | Queries | Bytes_data_sent | Bytes_data_recv | Latency_ms |
+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+
| 600       | 192.168.1.107 | 3306     | ONLINE | 10       | 0        | 10     | 0       | 123457  | 9922280         | 0               | 658        | <--- new master
| 601       | 192.168.1.111 | 3306     | ONLINE | 2        | 6        | 14     | 0       | 1848302 | 91513537        | 7590137770      | 1044       |
| 601       | 192.168.1.109 | 3306     | ONLINE | 5        | 3        | 12     | 0       | 1688789 | 83717258        | 6927354689      | 220        |
| 601       | 192.168.1.107 | 3306     | ONLINE | 3        | 5        | 13     | 0       | 1834415 | 90789405        | 7524861792      | 658        |
| 601       | 192.168.1.104 | 3306     | ONLINE | 6        | 2        | 24     | 0       | 1667252 | 82509124        | 6789724589      | 265        |
+-----------+---------------+----------+--------+----------+----------+--------+---------+---------+-----------------+-----------------+------------+

In this case the servers were not behind the master and switch happened quite fast.

We can see that the WRITE operations that normally are an issue given the need to move around an VIP or change name resolution, have a very limited hiccup.

Read operations were not affected, at all.

Nice eh?

Do you know how long it takes to do a switch in this conditions?

real 0m2.710s yes 2.7 seconds.

This is another evidence that most of the time in case of switch with MHA is cause by the need to redirect traffic from A to B using the network.

Crash fail-over

What happened if instead have a nice switch we have to cover a real failover?

First of all let us start masterha_manager:

nohup masterha_manager --conf=/etc/mha.cnf --wait_on_monitor_error=60 --wait_on_failover_error=60 >> /tmp/mha.log 2>&1

Then let us start some load again.

Finally go to the MySQL node that us master xxx.xxx.xxx.107

ps aux|grep mysql
mysql    18755  0.0  0.0 113248  1608 pts/0    S    Aug28   0:00 /bin/sh /opt/mysql_templates/mysql-57/bin/mysqld_safe --defaults-file=/opt/mysql_instances/mha1/my.cnf
mysql    21975  3.2 30.4 4398248 941748 pts/0  Sl   Aug28  93:21 /opt/mysql_templates/mysql-57/bin/mysqld --defaults-file=/opt/mysql_instances/mha1/my.cnf --basedir=/opt/mysql_templates/mysql-57/ --datadir=/opt/mysql_instances/mha1/data --plugin-dir=/opt/mysql_templates/mysql-57//lib/plugin --log-error=/opt/mysql_instances/mha1/mysql-3306.err --open-files-limit=65536 --pid-file=/opt/mysql_instances/mha1/mysql.pid --socket=/opt/mysql_instances/mha1/mysql.sock --port=3306

And kill the MySQL process.

kill -9 21975 18755

As before let us check what happened application side:

[  80s] threads: 4, tps: 213.20, reads: 1919.10, writes: 853.20, response time: 28.74ms (95%), errors: 0.00, reconnects:  0.00
[  90s] threads: 4, tps: 211.30, reads: 1901.80, writes: 844.70, response time: 28.63ms (95%), errors: 0.00, reconnects:  0.00
[ 100s] threads: 4, tps: 211.90, reads: 1906.40, writes: 847.90, response time: 28.60ms (95%), errors: 0.00, reconnects:  0.00
[ 110s] threads: 4, tps: 211.10, reads: 1903.10, writes: 845.30, response time: 29.27ms (95%), errors: 0.30, reconnects:  0.00 <-- issue starts
[ 120s] threads: 4, tps: 198.30, reads: 1785.10, writes: 792.40, response time: 28.43ms (95%), errors: 0.00, reconnects:  0.00
[ 130s] threads: 4, tps: 0.00, reads: 0.60, writes: 0.00, response time: 0.00ms (95%), errors: 0.00, reconnects:  0.40         <-- total stop in write
[ 140s] threads: 4, tps: 173.80, reads: 1567.80, writes: 696.30, response time: 34.89ms (95%), errors: 0.40, reconnects:  0.00 <-- writes restart
[ 150s] threads: 4, tps: 195.20, reads: 1755.10, writes: 780.50, response time: 33.98ms (95%), errors: 0.00, reconnects:  0.00
[ 160s] threads: 4, tps: 196.90, reads: 1771.30, writes: 786.80, response time: 33.49ms (95%), errors: 0.00, reconnects:  0.00
[ 170s] threads: 4, tps: 193.70, reads: 1745.40, writes: 775.40, response time: 34.39ms (95%), errors: 0.00, reconnects:  0.00
[ 180s] threads: 4, tps: 191.60, reads: 1723.70, writes: 766.20, response time: 35.82ms (95%), errors: 0.00, reconnects:  0.00

So it takes ~10 seconds to perform failover.

To better understand let see what happened on MHA-land:

Tue Aug 30 09:33:33 2016 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Tue Aug 30 09:33:33 2016 - [info] Reading application default configuration from /etc/mha.cnf..
... Read conf and start
Tue Aug 30 09:33:47 2016 - [debug] Trying to get advisory lock..
Tue Aug 30 09:33:47 2016 - [info] Ping(SELECT) succeeded, waiting until MySQL doesn't respond..
... Wait for errors
Tue Aug 30 09:34:47 2016 - [warning] Got error on MySQL select ping: 2006 (MySQL server has gone away) <--- Error time
Tue Aug 30 09:34:56 2016 - [warning] Connection failed 4 time(s)..                                     <--- Finally MHA decide to do something 
Tue Aug 30 09:34:56 2016 - [warning] Master is not reachable from health checker!
Tue Aug 30 09:34:56 2016 - [warning] Master mha2r(192.168.1.107:3306) is not reachable!
Tue Aug 30 09:34:56 2016 - [warning] SSH is reachable.
Tue Aug 30 09:34:58 2016 - [info] Master failover to mha1r(192.168.1.104:3306) completed successfully. <--- end of the failover

MHA sees the server failing at xx:47, but because the retry and checks validation it actually fully acknowledge the downtime at xx:56.

As such ~8 seconds after.

To perform the whole failover it then takes only ~2 seconds (again).

No movable IP or dns involve and as such the operations were fast.

This is obviously true in case the servers have the binary-log there, different story may be if MHA has also to manage and push data from binarylog to MySQL.

As you can see ProxySQL may help a lot in reducing the timing also for this scenario, totally skipping the network related operations, that as we know, are the ones causing more trouble in these cases.

How to stop an offending query with ProxySQL

halt_man All of us are very good in writing good queries, we know that ;) but sometimes a bad query may escape our control and hit (badly) our database.

There is also that probie, who just join the company and is writing all his code with SELECT * and no WHERE.

We have told him millions of time that doing this is bad, but he seems not listening.

Ah the other day we had another code injection that developers will take some time to fix, and that take them some time to isolate the part of the code sending the killing query to our database.

All the above are true stories, things that happen every day in at least few environments.

The main problem in that case is not to isolate the bad query, that is something that we can do very fast, but to identify the code that is generating it and disable that part of the code without killing the whole application.

That part can takes days.

ProxySQL allow us to act fast and stop any offending query in seconds.

I will show you how.

Let us say we have an offending query that does this:

SELECT * FROM history;

Where history is a table of 2 Tb partitioned by year in our DWH.

A query like that will certainly create some issue on the database, it is obviously bad design, and easy to identify.

Unfortunately it was inserted in the ETL process that use multi thread approach and autorecovery.

As such whenever you kill it, the process will restart it, and the developers will take some time to stop that.

In the meantime your reporting system serving your company real time is so slooow or down.

With ProxySQL you will stop that query in 1 second:

INSERT INTO mysql_query_rules (rule_id, active, match_pattern, error_msg, apply) VALUES (89,1,'^SELECT \* from history$','Query not allowed',1);
LOAD MYSQL QUERY RULES TO RUNTIME;SAVE MYSQL QUERY RULES TO DISK;

Done, your DB will never receive that query again, and the application will get a message saying that the query is not allowed.

But it is possible to do things even better:

INSERT INTO mysql_query_rules (rule_id, active, match_digest, flagOUT, apply) VALUES (89,1,'^SELECT \* FROM history', 100, 0);
INSERT INTO mysql_query_rules (rule_id, active, flagIN, match_digest, destination_hostgroup, apply) VALUES (1001,1, 100, 'WHERE', 502, 1);
INSERT INTO mysql_query_rules (rule_id, active, flagIN, error_msg, apply) VALUES (1002,1, 100, 'Query not allowed', 1);
LOAD MYSQL QUERY RULES TO RUNTIME;SAVE MYSQL QUERY RULES TO DISK;

In this case ProxySQL will check for any query having SELECT * FROM history.

If the query has a WHERE clause then it will redirect to the server for execution.

If the query does not have a WHERE it will be stop and an error message sent to the application.

Conclusion

The one above is a very simple almost basic example of offending query.

But I am sure it makes clear how ProxySQL can come in help to any DBA to stop them quickly in case of emergency.

Giving the DBAs and the developers time to coordinate a better plan of action to permanently fix the issue.

References

https://github.com/sysown/proxysql
http://www.proxysql.com/2015/09/proxysql-tutorial-setup-in-mysql.html
https://github.com/sysown/proxysql/blob/v1.2.2/doc/configuration_howto.md
https://github.com/sysown/proxysql/blob/v1.2.2/INSTALL.md

Sharding with ProxySQL

mysql_proxysql Recently a colleague of mine ask me to provide a simple example on how ProxySQL can perform sharding.
ProxySQL is a very powerful platform that allow us to manipulate and manage our connections and query in a simple but effective way.
In this article I will show you how.

{autotoc enabled=yes}

Before starting is better to clarify some basic concepts.

ProxySQL organize its internal set of servers in Host Groups (HG), each HG can be associate to users and to Query Rules (QR).

Each QR can be final (apply = 1) or can let ProxySQL continue to parse other QR.

A QR can be a rewrite action, or can be a simple match, it can have a specific target HG, or be generic, finally QR are defined using regex.

You can see QR as a sequence of filters and transformation that you can arrange as you like.

These simple basic rules give us enormous flexibility, and allow us to create very simple actions, like a simple query re-write or very complex chains that could see dozens of QR concatenated.

Documentation can be found here

The information related to HG or QR is easily accessible using the the ProxySQL administrator interface, in the tables mysql_servers, mysql_query_rules and stats.stats_mysql_query_rules; the last one allow us to evaluate if and how the rule(s) is used.

About sharding, what ProxySQL can do for us to achieve what we need in a (relatively easy) way?

Some people/company include sharding logic in the application, and use multiple connection to reach the different targets, or have some logic to split the load across several schemas/tables.

ProxySQL allow us to simplify the way connectivity and query distribution is suppose to work reading data in the query or accepting HINTS.

No matter which kind of requirements the sharding exercise can be summarize in few different categories.

By split the data inside the same container (like having a shard by State where each State is a schema)
By physical data location (this can have multiple mysql servers in the same room, as well as having them geographically distributed)
Combination of the two, where I do split by state using a server dedicated and again split by schema/table by whatever (say by gender)

In the following examples I will show how to use ProxySQL to cover the three different scenario defined above and a bit more.

The example below will report text from the Admin ProxySQL interface and from MySQL console.I will mark each one as follow:

Mc for MySQL console
Pa for ProxySQL Admin

Please note that mysql console MUST use the -c flag to pass the comments in the query. This because the default behaviour, in mysql console, is to remove the comments.

I am going to illustrate procedures that you can replicate on your laptop.

This because I want you to test directly the ProxySQL functionalities.

For the example describe below I have used PrxySQL v1.2.2 that is going to become the master in few days.

You can download it from :

git clone https://github.com/sysown/proxysql.git
git checkout v1.2.2
Then to compile :
cd make
make install

If you need full instructions on how to install and configure ProxySQL than read here and here

Finally you need to have the WORLD test db loaded, world test DB can be found here

First example/exercise is :

Shard inside the same MySQL Server using 3 different schemas split by continent.

Obviously you can have any number of shards and number of relative schemas.

What is relevant here is to demonstrate how traffic can be redirect to different targets (schemas) maintaining the same structure (tables).

This discriminating the target on the base of some relevant information in the Data or pass by the application.

Ok let us roll the ball.

Having :

[Mc]
+---------------+-------------+
| Continent     | count(Code) |
+---------------+-------------+
| Asia          |          51 | <--
| Europe        |          46 | <--
| North America |          37 | 
| Africa        |          58 | <-- 
| Oceania       |          28 |
| Antarctica    |           5 |
| South America |          14 |
+---------------+-------------+

For this exercise you can use single host or multiple servers in replica.

Summarizing you will need:

3 hosts: 192.168.1.[5-6-7] (only one needed now but the others are for future use)
3 schemas: Continent X + world schema
1 user : user_shardRW
3 hostgroups: 10, 20, 30 (for future use)

We will create the following Schemas Asia, Africa, Europe first.

[Mc]
CREATE schema [Asia|Europe|Africa];
CREATE TABLE Asia.City AS SELECT a.* FROM  world.City a JOIN Country ON a.CountryCode = Country.code WHERE Continent='Asia' ;
CREATE TABLE Europe.City AS SELECT a.* FROM  world.City a JOIN Country ON a.CountryCode = Country.code WHERE Continent='Europe' ;
CREATE TABLE Africa.City AS SELECT a.* FROM  world.City a JOIN Country ON a.CountryCode = Country.code WHERE Continent='Africa' ;
 
CREATE TABLE Asia.Country AS SELECT * FROM  world.Country WHERE Continent='Asia' ;
CREATE TABLE Europe.Country AS SELECT * FROM  world.Country WHERE Continent='Europe' ;
CREATE TABLE Africa.Country AS SELECT * FROM  world.Country  WHERE Continent='Africa' ;

Create the user:

[Mc]
GRANT ALL ON *.* TO user_shardRW@'%' IDENTIFIED BY 'test';

Now let us start to configure the ProxySQL:

[Pa]
INSERT INTO mysql_users (username,password,active,default_hostgroup,default_schema) VALUES ('user_shardRW','test',1,10,'test_shard1');
LOAD MYSQL USERS TO RUNTIME;SAVE MYSQL USERS TO DISK;
 
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.5',10,3306,100);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.6',20,3306,100);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.7',30,3306,100);
LOAD MYSQL SERVERS TO RUNTIME; SAVE MYSQL SERVERS TO DISK;

With this we have defined the User, the servers and the Host groups.

Let us start to define the logic with the query rules:

[Pa]

DELETE FROM mysql_query_rules WHERE rule_id > 30;
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,replace_pattern,apply) VALUES (31,1,'user_shardRW',"^SELECT\s*(.*)\s*from\s*world.(\S*)\s(.*).*Continent='(\S*)'\s*(\s*.*)$","SELECT \1 from \4.\2 WHERE 1=1 \5",1);
LOAD MYSQL QUERY RULES TO RUNTIME;SAVE MYSQL QUERY RULES TO DISK;

I am now going to query the master (or a single node) but I am expecting ProxySQL to redirect the query to the right shard catching the value of the Continent.

[Mc]
 SELECT name,population FROM world.City  WHERE Continent='Europe' AND CountryCode='ITA' ORDER BY population DESC LIMIT 1;
+------+------------+
| name | population |
+------+------------+
| Roma |    2643581 |
+------+------------+

Well you can say ... "hey you are querying the schema world, of course you get back the correct data".

But this is not what had really happened, ProxySQL did not query the schema world but the schema Europe.

Let see the details:

[Pa]
SELECT * FROM stats_mysql_query_digest;
Original    :SELECT name,population FROM world.City  WHERE Continent='Europe' AND CountryCode='ITA' ORDER BY population DESC LIMIT 1;
Transformed :SELECT name,population FROM Europe.City WHERE ?=? AND CountryCode=? ORDER BY population DESC LIMIT ?

Let me explain what happened.
Rule 31 in ProxySQL will take all the FIELDS we will pass in the query, it will catch the CONTINENT in the where clause, it will take any condition after the WHERE and it will reorganize the query all using the RegEx.

Does this works for any table in the sharded schemas
Of course it does.
A query like:

SELECT name,population FROM world.Country WHERE Continent='Asia' ;

Will be transformed into:

SELECT name,population FROM Asia.Country WHERE ?=?

[Mc]
+----------------------+------------+
| name                 | population |
+----------------------+------------+
| Afghanistan          |   22720000 |
| United Arab Emirates |    2441000 |
| Armenia              |    3520000 |
<snip ...>
| Vietnam              |   79832000 |
| Yemen                |   18112000 |
+----------------------+------------+

Another possible a approach to instruct ProxySQL to shard is:

Pass a hint inside a comment.

Let see how.

First let me disable the rule I have just insert, this is not really needed but so you can see how :)

[Pa]
mysql> UPDATE mysql_query_rules SET active=0 WHERE rule_id=31;
Query OK, 1 row affected (0.00 sec)
mysql> LOAD MYSQL QUERY RULES TO RUNTIME;SAVE MYSQL QUERY RULES TO DISK;
Query OK, 0 rows affected (0.00 sec)

Done.

Now what I want to have is that *ANY* query that contains comment /* continent=X */ should go to the continent X schema, same server.

To do so, I will instruct ProxySQL to replace any reference to the world schema inside the the query I am going to submit.

[Pa]
DELETE FROM mysql_query_rules WHERE rule_id IN (31,33,34,35,36);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,replace_pattern,apply,FlagOUT,FlagIN) VALUES (31,1,'user_shardRW',"\S*\s*\/\*\s*continent=.*Asia\s*\*.*",NULL,0,23,0);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,replace_pattern,apply,FlagIN,FlagOUT) VALUES (32,1,'user_shardRW','world.','Asia.',0,23,23);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,replace_pattern,apply,FlagOUT,FlagIN) VALUES (33,1,'user_shardRW',"\S*\s*\/\*\s*continent=.*Europe\s*\*.*",NULL,0,25,0);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,replace_pattern,apply,FlagIN,FlagOUT) VALUES (34,1,'user_shardRW','world.','Europe.',0,25,25);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,replace_pattern,apply,FlagOUT,FlagIN) VALUES (35,1,'user_shardRW',"\S*\s*\/\*\s*continent=.*Africa\s*\*.*",NULL,0,24,0);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,replace_pattern,apply,FlagIN,FlagOUT) VALUES (36,1,'user_shardRW','world.','Africa.',0,24,24);
LOAD MYSQL QUERY RULES TO RUNTIME;SAVE MYSQL QUERY RULES TO DISK;

How this works?

I have defined mainly to concatenated rules.

The first capture the incoming query that contains the desired value (like continent = Asia).

If the match is there ProxySQL will exit that action, but while doing so it will read the Apply field and if Apply is 0 it will read the FlagOUT value. At this point it will go to the first rule (in sequence) that has the value of FlagIN equal to the FlagOUT.

The second rule will get the request and will replace the value of world with the one I have define.

In short it will replace whatever is in the match_pattern with the value that is in the replace_pattern.
Now what happens here is that ProxySQL implement the Re2 google library for RegEx.

Re2 is very fast but has some limitations, like it does NOT support (at the time of the writing) the flag option g.

In other words if I have a select with many tables and as such several "world." Re2 will replace ONLY the first instance.

As such a query like:

SELECT /* continent=Europe */ * FROM world.Country JOIN world.City ON world.City.CountryCode=world.Country.Code WHERE Country.code='ITA' ;

Will be transformed into :

SELECT /* continent=Europe */ * FROM Europe.Country JOIN world.City ON world.City.CountryCode=world.Country.Code WHERE Country.code='ITA' ;

And fail.

The other day with Rene' we were discussing how to solve this given the lack of implementation in Re2. Finally we had opted for recursive actions.

What this means?

It means that ProxySQL from v1.2.2 now has a new functionality that allow recursive calls to a Query Rule, the maximum number of iterations that ProxySQL can run, is managed by the option (global variable) mysql-query_processor_iterations.

Mysql-query_processor_iterations define how many operation, a query process can execute as whole (from start to end).

This new implementation allow us to reference a Query Rule to itself in order to be executed multiple times.

If you go back you will noticed that QR 34 has FlagIN and FlagOUT pointing to the same value of 25 and Apply =0.

This will bring ProxySQL to recursively call rule 34 until it change ALL the value of the word world.

The result is the following:

[Mc]
SELECT /* continent=Europe */ Code, City.Name, City.population  FROM world.Country JOIN world.City ON world.City.CountryCode=world.Country.Code WHERE City.population > 10000 GROUP BY Name ORDER BY City.Population DESC LIMIT 5;
+------+---------------+------------+
| Code | Name          | population |
+------+---------------+------------+
| RUS  | Moscow        |    8389200 |
| GBR  | London        |    7285000 |
| RUS  | St Petersburg |    4694000 |
| DEU  | Berlin        |    3386667 |
| ESP  | Madrid        |    2879052 |
+------+---------------+------------+

You can see ProxySQL internal information using the following queries:

[Pa]
 SELECT active,hits, mysql_query_rules.rule_id, match_digest, match_pattern, replace_pattern, cache_ttl, apply,flagIn,flagOUT FROM mysql_query_rules NATURAL JOIN stats.stats_mysql_query_rules ORDER BY mysql_query_rules.rule_id;
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+
| active | hits | rule_id | match_digest        | match_pattern                          | replace_pattern | cache_ttl | apply | flagIN | flagOUT |
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+
| 1      | 1    | 33      | NULL                | \S*\s*\/\*\s*continent=.*Europe\s*\*.* | NULL            | NULL      | 0     | 0      | 25      | <--
| 1      | 4    | 34      | NULL                | world.                                 | Europe.         | NULL      | 0     | 25     | 25      | <--
| 1      | 0    | 35      | NULL                | \S*\s*\/\*\s*continent=.*Africa\s*\*.* | NULL            | NULL      | 0     | 0      | 24      |
| 1      | 0    | 36      | NULL                | world.                                 | Africa.         | NULL      | 0     | 24     | 24      |
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+

And

[Pa]
SELECT * FROM stats_mysql_query_digest;
<snip AND taking only digest_text>
SELECT Code, City.Name, City.population FROM Europe.Country JOIN Europe.City ON Europe.City.CountryCode=Europe.Country.Code WHERE City.population > ? GROUP BY Name ORDER BY City.Population DESC LIMIT ?

As you can see ProxySQL has nicely replace the word world.

And executed only on the desired schema.

How I can shard redirecting the queries to an Host?

(Instead of a schema)This is even easier :)

The main point is that whatever match the rule, should go to a defined HG.No rewrite imply which means less work.

So how this is done?As said before I have 3 NODES 192.168.1.[5-6-7]For this example I will use world db (no continent schema), distributed in each node, and I wil retrieve the node bind IP to be sure I am going on the right place.

What I will do is to instruct ProxySQL to send my query by using a HINT to a specific host.

I choose the hint "shard_host_HG" and I am going to inject it in the query as comment.

As such the Query Rules will be:

[Pa]
DELETE FROM mysql_query_rules WHERE rule_id IN (40,41,42, 10,11,12);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,destination_hostgroup,apply) VALUES (10,1,'user_shardRW',"\/\*\s*shard_host_HG=.*Europe\s*\*.",10,0);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,destination_hostgroup,apply) VALUES (11,1,'user_shardRW',"\/\*\s*shard_host_HG=.*Asia\s*\*.",20,0);
INSERT INTO mysql_query_rules (rule_id,active,username,match_pattern,destination_hostgroup,apply) VALUES (12,1,'user_shardRW',"\/\*\s*shard_host_HG=.*Africa\s*\*.",30,0);
LOAD MYSQL QUERY RULES TO RUNTIME;SAVE MYSQL QUERY RULES TO DISK;

While the queries I am going to test are:

[Mc]
SELECT /* shard_host_HG=Europe */ City.Name, City.Population FROM world.Country JOIN world.City ON world.City.CountryCode=world.Country.Code WHERE Country.code='ITA' LIMIT 5; SELECT * /* shard_host_HG=Europe */ FROM information_schema.GLOBAL_VARIABLES WHERE variable_name LIKE 'bind%';
SELECT /* shard_host_HG=Asia */ City.Name, City.Population FROM world.Country JOIN world.City ON world.City.CountryCode=world.Country.Code WHERE Country.code='IND' LIMIT 5; SELECT * /* shard_host_HG=Asia */ FROM information_schema.GLOBAL_VARIABLES WHERE variable_name LIKE 'bind%';
SELECT /* shard_host_HG=Africa */ City.Name, City.Population FROM world.Country JOIN world.City ON world.City.CountryCode=world.Country.Code WHERE Country.code='ETH' LIMIT 5; SELECT * /* shard_host_HG=Africa */ FROM information_schema.GLOBAL_VARIABLES WHERE variable_name LIKE 'bind%';

Running the query for Africa, I will get:

[Mc]
SELECT /* shard_host_HG=Africa */ City.Name, City.Population FROM world.Country JOIN world.City ON world.City.CountryCode=world.Country.Code WHERE Country.code='ETH' LIMIT 5; SELECT * /* shard_host_HG=Africa */ FROM information_schema.GLOBAL_VARIABLES WHERE variable_name LIKE 'bind%';
+-------------+------------+
| Name        | Population |
+-------------+------------+
| Addis Abeba |    2495000 |
| Dire Dawa   |     164851 |
| Nazret      |     127842 |
| Gonder      |     112249 |
| Dese        |      97314 |
+-------------+------------+
+---------------+----------------+
| VARIABLE_NAME | VARIABLE_VALUE |
+---------------+----------------+
| BIND_ADDRESS  | 192.168.1.7    |
+---------------+----------------+

That will give me :

[Pa]
SELECT active,hits, mysql_query_rules.rule_id, match_digest, match_pattern, replace_pattern, cache_ttl, apply,flagIn,flagOUT FROM mysql_query_rules NATURAL JOIN stats.stats_mysql_query_rules ORDER BY mysql_query_rules.rule_id;
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+
| active | hits | rule_id | match_digest        | match_pattern                          | replace_pattern | cache_ttl | apply | flagIN | flagOUT |
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+
| 1      | 0    | 40      | NULL                | \/\*\s*shard_host_HG=.*Europe\s*\*.    | NULL            | NULL      | 0     | 0      | 0       |
| 1      | 0    | 41      | NULL                | \/\*\s*shard_host_HG=.*Asia\s*\*.      | NULL            | NULL      | 0     | 0      | 0       |
| 1      | 2    | 42      | NULL                | \/\*\s*shard_host_HG=.*Africa\s*\*.    | NULL            | NULL      | 0     | 0      | 0       | <-- Note the HITS (2 as the run queries)
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+

In this example we have NO replace_pattern this is only a matching and redirecting Rule, where the destination HG is defined in the value of destination_hostgroup attribute while inserting.

In the case for Africa is HG 30.

The server in HG 30 is:

[Pa]
SELECT hostgroup_id,hostname,port,STATUS FROM mysql_servers ;
+--------------+-------------+------+--------+
| hostgroup_id | hostname    | port | STATUS |
+--------------+-------------+------+--------+
| 10           | 192.168.1.5 | 3306 | ONLINE |
| 20           | 192.168.1.6 | 3306 | ONLINE |
| 30           | 192.168.1.7 | 3306 | ONLINE | <---
+--------------+-------------+------+--------+

Which match perfectly with our returned value.

You can try by your own the other two continents.

Using destination_hostgroup

Another way to assign to which final host a query should go is to use the the destination_hostgroup, set the Schema_name attribute and use the use schema syntax in the query.

like:

[Pa]
INSERT INTO mysql_query_rules (active,schemaname,destination_hostgroup,apply) VALUES
(1, 'shard00', 1, 1), (1, 'shard01', 1, 1), (1, 'shard03', 1, 1),
(1, 'shard04', 2, 1), (1, 'shard06', 2, 1), (1, 'shard06', 2, 1),
(1, 'shard07', 3, 1), (1, 'shard08', 3, 1), (1, 'shard09', 3, 1);

And then in the query do something like :

USE shard02; SELECT * FROM tablex;

I mention this method because is one of the most common at the moment in large companies using SHARDING.

But it is not safe, because it relays on the fact the query will be execute in the desired HG.

While the risk of error is high.

Just think if a query doing join against a specified SHARD:

USE shard01; SELECT * FROM tablex JOIN shard03 ON tablex.id = shard03.tabley.id;

This will probably generate an error because shard03 is probably NOT present on the host containing shar01.

As such this approach can be used ONLY when you are 100% sure about what you are doing and when you are sure NO query will have explicit schema declaration.

Shard By Host and by Schema

Finally is obviously possible to combine the two approaches sharding by host and have only a subset of schemas

To do so let us use all the 3 nodes and have the schema distribute as follow:

Europe on Server 192.168.1.5 -> HG 10
Asia on Server 192.168.1.6 -> HG 20
Africa on Server 192.168.1.7 -> HG 30

I have already set the query rules both using HINT so what I have to do is to use them BOTH to combine the operations:

[Mc]
SELECT /* shard_host_HG=Asia */ /* continent=Asia */  City.Name, City.Population FROM world.Country JOIN world.City ON world.City.CountryCode=world.Country.Code WHERE Country.code='IND' LIMIT 5; SELECT * /* shard_host_HG=Asia */ FROM information_schema.GLOBAL_VARIABLES WHERE variable_name LIKE 'bind%';
+--------------------+------------+
| Name               | Population |
+--------------------+------------+
| Mumbai (Bombay)    |   10500000 |
| Delhi              |    7206704 |
| Calcutta [Kolkata] |    4399819 |
| Chennai (Madras)   |    3841396 |
| Hyderabad          |    2964638 |
+--------------------+------------+
5 rows IN SET (0.00 sec)
 
+---------------+----------------+
| VARIABLE_NAME | VARIABLE_VALUE |
+---------------+----------------+
| BIND_ADDRESS  | 192.168.1.6    |
+---------------+----------------+
1 row IN SET (0.01 sec)

[Pa]
mysql> SELECT digest_text FROM stats_mysql_query_digest;
+--------------------------------------------------------------------------------------------------------------------------------------------+
| digest_text                                                                                                                                |
+--------------------------------------------------------------------------------------------------------------------------------------------+
| SELECT * FROM information_schema.GLOBAL_VARIABLES WHERE variable_name LIKE ?                                                               |
| SELECT City.Name, City.Population FROM Asia.Country JOIN Asia.City ON Asia.City.CountryCode=Asia.Country.Code WHERE Country.code=? LIMIT ? |
+--------------------------------------------------------------------------------------------------------------------------------------------+
2 rows IN SET (0.00 sec)
 
mysql> SELECT active,hits, mysql_query_rules.rule_id, match_digest, match_pattern, replace_pattern, cache_ttl, apply,flagIn,flagOUT FROM mysql_query_rules NATURAL JOIN stats.stats_mysql_query_rules ORDER BY mysql_query_rules.rule_id;
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+
| active | hits | rule_id | match_digest        | match_pattern                          | replace_pattern | cache_ttl | apply | flagIN | flagOUT |
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+
| 1      | 0    | 10      | NULL                | \/\*\s*shard_host_HG=.*Europe\s*\*.    | NULL            | NULL      | 0     | 0      | NULL    |
| 1      | 2    | 11      | NULL                | \/\*\s*shard_host_HG=.*Asia\s*\*.      | NULL            | NULL      | 0     | 0      | NULL    |
| 1      | 0    | 12      | NULL                | \/\*\s*shard_host_HG=.*Africa\s*\*.    | NULL            | NULL      | 0     | 0      | NULL    |
| 1      | 0    | 13      | NULL                | NULL                                   | NULL            | NULL      | 0     | 0      | 0       |
| 1      | 1    | 31      | NULL                | \S*\s*\/\*\s*continent=.*Asia\s*\*.*   | NULL            | NULL      | 0     | 0      | 23      |
| 1      | 4    | 32      | NULL                | world.                                 | Asia.           | NULL      | 0     | 23     | 23      |
| 1      | 0    | 33      | NULL                | \S*\s*\/\*\s*continent=.*Europe\s*\*.* | NULL            | NULL      | 0     | 0      | 25      |
| 1      | 0    | 34      | NULL                | world.                                 | Europe.         | NULL      | 0     | 25     | 25      |
| 1      | 0    | 35      | NULL                | \S*\s*\/\*\s*continent=.*Africa\s*\*.* | NULL            | NULL      | 0     | 0      | 24      |
| 1      | 0    | 36      | NULL                | world.                                 | Africa.         | NULL      | 0     | 24     | 24      |
+--------+------+---------+---------------------+----------------------------------------+-----------------+-----------+-------+--------+---------+

As you can see rule 11 has two HITS, which means my queries will go to the associated HG.

But given Apply for rule 11 is =0, ProxySQL will first continue to process the QueryRules.

As such it will also transform the queries as for rules 31 and 32, each one having the expected number of hits (1 the first and the 4 because the loop, the second).

How to shard base on a MOD

to shard base on a MOD value Like handle table sharding based on the mod of the user id?

such that `insert into 'foo' ('user_id', 'name') values (180, 'bar')` becomes `insert into 'foo_X ('user_id', 'name') values (180, 'bar')` based on 180 % 25, where 25 is the number of sharded tables.

Based on 180 % 25, where 25 is the number of sharded tables.

Solution is to create X number of query rules to manage the MOD value:

INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(00|25|50|75),","INSERT INTO foo_00 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(01|26|51|76),","INSERT INTO foo_01 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(02|27|52|77),","INSERT INTO foo_02 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(03|28|53|78),","INSERT INTO foo_03 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(04|29|54|79),","INSERT INTO foo_04 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(05|30|55|80),","INSERT INTO foo_05 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(06|31|56|81),","INSERT INTO foo_06 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(07|32|57|82),","INSERT INTO foo_07 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(08|33|58|83),","INSERT INTO foo_08 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(09|34|59|84),","INSERT INTO foo_09 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(10|35|60|85),","INSERT INTO foo_10 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(11|36|61|86),","INSERT INTO foo_11 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(12|37|62|87),","INSERT INTO foo_12 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(13|38|63|88),","INSERT INTO foo_13 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(14|39|64|89),","INSERT INTO foo_14 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(15|40|65|90),","INSERT INTO foo_15 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(16|41|66|91),","INSERT INTO foo_16 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(17|42|67|92),","INSERT INTO foo_17 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(18|43|68|93),","INSERT INTO foo_18 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(19|44|69|94),","INSERT INTO foo_19 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(20|45|70|95),","INSERT INTO foo_20 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(21|46|71|96),","INSERT INTO foo_21 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(22|47|72|97),","INSERT INTO foo_22 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(23|48|73|98),","INSERT INTO foo_23 (user_id,name) VALUES(\1\2,",1);
INSERT INTO mysql_query_rules (active, match_pattern, replace_pattern, apply) VALUES (1, "INSERT INTO foo \(user_id,name\) VALUES \((\d+)(24|49|74|99),","INSERT INTO foo_24 (user_id,name) VALUES(\1\2,",1);
LOAD MYSQL QUERY RULES TO RUNTIME;

As you can see below this solution allow the transparent assignment using MOD 25

mysql> CREATE TABLE foo_00 (user_id INT, name VARCHAR(30));
mysql> CREATE TABLE foo_01 (user_id INT, name VARCHAR(30));
mysql> CREATE TABLE foo_02 (user_id INT, name VARCHAR(30));
mysql> CREATE TABLE foo_03 (user_id INT, name VARCHAR(30));
mysql> CREATE TABLE foo_04 (user_id INT, name VARCHAR(30));
mysql> INSERT INTO foo (user_id,name) VALUES (1000,"nameA");
mysql> INSERT INTO foo (user_id,name) VALUES (7456076,"nameB");

SELECT * FROM foo_00;
+---------+-------+
| user_id | name  |
+---------+-------+
|    1000 | nameA |
+---------+-------+
mysql> SELECT * FROM foo_01;
+---------+-------+
| user_id | name  |
+---------+-------+
| 7456076 | nameB |
+---------+-------+

Credits

It is obvious that I need to acknowledge and kudo the work Rene' Cannao is doing to make ProxySQL a solid, fast and flexible product.

I have also to mention that I was and am working with him very often, more often than he likes, asking him fix and discussing with him optimization.

Requests that he try to satisfied with surprising speed and efficiency.

Reference

https://github.com/sysown/proxysql/tree/v1.2.2/doc
https://github.com/google/re2/wiki/Syntax
http://www.proxysql.com/2015/09/proxysql-tutorial-setup-in-mysql.html
https://github.com/sysown/proxysql/blob/v1.2.2/doc/configuration_howto.md
https://github.com/sysown/proxysql/blob/v1.2.2/INSTALL.md
https://dev.mysql.com/doc/index-other.html

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How to shard base on a MOD

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