Load balance with ProxySQL¶

ProxySQL is a high-performance SQL proxy. ProxySQL runs as a daemon watched by a monitoring process. The process monitors the daemon and restarts it in case of a crash to minimize downtime.

The daemon accepts incoming traffic from MySQL clients and forwards it to backend MySQL servers.

The proxy is designed to run continuously without needing to be restarted. Most configuration can be done at runtime using queries similar to SQL statements in the ProxySQL admin interface. These include runtime parameters, server grouping, and traffic-related settings.

Manual configuration¶

This section describes how to configure ProxySQL with three Percona XtraDB Cluster nodes.

Node	Host Name	IP address
Node 1	pxc1	192.168.70.71
Node 2	pxc2	192.168.70.72
Node 3	pxc3	192.168.70.73
Node 4	proxysql	192.168.70.74

ProxySQL can be configured either using the /etc/proxysql.cnf file or through the admin interface. The admin interface is recommended because this interface can dynamically change the configuration without restarting the proxy.

To connect to the ProxySQL admin interface, you need a mysql client. You can either connect to the admin interface from Percona XtraDB Cluster nodes that already have the mysql client installed (Node 1, Node 2, Node 3) or install the client on Node 4 and connect locally. For this tutorial, install Percona XtraDB Cluster on Node 4:

Changes in the installation procedure

In Percona XtraDB Cluster 8.0, ProxySQL is not installed automatically as a dependency of the percona-xtradb-cluster-client-8.0 package. You should install the proxysql package separately.

Note

ProxySQL has multiple versions in the version 2 series.

On Debian or Ubuntu for ProxySQL 2.x:

root@proxysql:~# apt install percona-xtradb-cluster-client
root@proxysql:~# apt install proxysql2

On Red Hat Enterprise Linux or CentOS for ProxySQL 2.x:

$ sudo yum install Percona-XtraDB-Cluster-client-80
$ sudo yum install proxysql2

To connect to the admin interface, use the credentials, host name and port specified in the global variables.

Warning

Do not use default credentials in production!

The following example shows how to connect to the ProxySQL admin interface with default credentials:

root@proxysql:~# mysql -u admin -padmin -h 127.0.0.1 -P 6032

Expected output

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.5.30 (ProxySQL Admin Module)

Copyright (c) 2009-2020 Percona LLC and/or its affiliates
Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql@proxysql>

To see the ProxySQL databases and tables use the following commands:

mysql@proxysql> SHOW DATABASES;

The following output shows the ProxySQL databases:

Expected output

+-----+---------+-------------------------------+
| seq | name    | file                          |
+-----+---------+-------------------------------+
| 0   | main    |                               |
| 2   | disk    | /var/lib/proxysql/proxysql.db |
| 3   | stats   |                               |
| 4   | monitor |                               |
+-----+---------+-------------------------------+
4 rows in set (0.00 sec)

mysql@proxysql> SHOW TABLES;

The following output shows the ProxySQL tables:

Expected output

+--------------------------------------+
| tables                               |
+--------------------------------------+
| global_variables                     |
| mysql_collations                     |
| mysql_query_rules                    |
| mysql_replication_hostgroups         |
| mysql_servers                        |
| mysql_users                          |
| runtime_global_variables             |
| runtime_mysql_query_rules            |
| runtime_mysql_replication_hostgroups |
| runtime_mysql_servers                |
| runtime_scheduler                    |
| scheduler                            |
+--------------------------------------+
12 rows in set (0.00 sec)

For more information about admin databases and tables, see Admin Tables

Note

The ProxySQL configuration can reside in the following areas:

MEMORY (your current working place)
RUNTIME (the production settings)
DISK (durable configuration, saved inside an SQLITE database)

When you change a parameter, you change it in MEMORY area. This ability is by design and lets you test the changes before pushing the change to production (RUNTIME), or save the change to disk.

Add cluster nodes to ProxySQL¶

To configure the backend Percona XtraDB Cluster nodes in ProxySQL, insert corresponding records into the mysql_servers table.

Note

ProxySQL uses the concept of hostgroups to group cluster nodes. This enables you to balance the load in a cluster by routing different types of traffic to different groups. There are many ways you can configure hostgroups (for example, source and replicas, read and write load, etc.) and a every node can be a member of multiple hostgroups.

This example adds three Percona XtraDB Cluster nodes to the default hostgroup (0), which receives both write and read traffic:

mysql@proxysql> INSERT INTO mysql_servers(hostgroup_id, hostname, port) VALUES (0,'192.168.70.71',3306);
mysql@proxysql> INSERT INTO mysql_servers(hostgroup_id, hostname, port) VALUES (0,'192.168.70.72',3306);
mysql@proxysql> INSERT INTO mysql_servers(hostgroup_id, hostname, port) VALUES (0,'192.168.70.73',3306);

To see the nodes:

mysql@proxysql> SELECT * FROM mysql_servers;

The following output shows the list of nodes:

Expected output

+--------------+---------------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
| hostgroup_id | hostname      | port | status | weight | compression | max_connections | max_replication_lag | use_ssl | max_latency_ms | comment |
+--------------+---------------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
| 0            | 192.168.70.71 | 3306 | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
| 0            | 192.168.70.72 | 3306 | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
| 0            | 192.168.70.73 | 3306 | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
+--------------+---------------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
3 rows in set (0.00 sec)

Create ProxySQL monitoring user¶

To enable monitoring of Percona XtraDB Cluster nodes in ProxySQL, create a user with USAGE privilege on any node in the cluster and configure the user in ProxySQL.

The following example shows how to add a monitoring user on Node 2:

mysql@pxc2> CREATE USER 'proxysql'@'%' IDENTIFIED WITH mysql_native_password by '$3Kr$t';
mysql@pxc2> GRANT USAGE ON *.* TO 'proxysql'@'%';

The following example shows how to configure this user on the ProxySQL node:

mysql@proxysql> UPDATE global_variables SET variable_value='proxysql'
              WHERE variable_name='mysql-monitor_username';
mysql@proxysql> UPDATE global_variables SET variable_value='ProxySQLPa55'
              WHERE variable_name='mysql-monitor_password';

To load this configuration at runtime, issue a LOAD command. To save these changes to disk (ensuring that they persist after ProxySQL shuts down), issue a SAVE command.

mysql@proxysql> LOAD MYSQL VARIABLES TO RUNTIME;
mysql@proxysql> SAVE MYSQL VARIABLES TO DISK;

To ensure that monitoring is enabled, check the monitoring logs:

mysql@proxysql> SELECT * FROM monitor.mysql_server_connect_log ORDER BY time_start_us DESC LIMIT 6;

Expected output

+---------------+------+------------------+----------------------+---------------+
| hostname      | port | time_start_us    | connect_success_time | connect_error |
+---------------+------+------------------+----------------------+---------------+
| 192.168.70.71 | 3306 | 1469635762434625 | 1695                 | NULL          |
| 192.168.70.72 | 3306 | 1469635762434625 | 1779                 | NULL          |
| 192.168.70.73 | 3306 | 1469635762434625 | 1627                 | NULL          |
| 192.168.70.71 | 3306 | 1469635642434517 | 1557                 | NULL          |
| 192.168.70.72 | 3306 | 1469635642434517 | 2737                 | NULL          |
| 192.168.70.73 | 3306 | 1469635642434517 | 1447                 | NULL          |
+---------------+------+------------------+----------------------+---------------+
6 rows in set (0.00 sec)

mysql> SELECT * FROM monitor.mysql_server_ping_log ORDER BY time_start_us DESC LIMIT 6;

Expected output

+---------------+------+------------------+-------------------+------------+
| hostname      | port | time_start_us    | ping_success_time | ping_error |
+---------------+------+------------------+-------------------+------------+
| 192.168.70.71 | 3306 | 1469635762416190 | 948               | NULL       |
| 192.168.70.72 | 3306 | 1469635762416190 | 803               | NULL       |
| 192.168.70.73 | 3306 | 1469635762416190 | 711               | NULL       |
| 192.168.70.71 | 3306 | 1469635702416062 | 783               | NULL       |
| 192.168.70.72 | 3306 | 1469635702416062 | 631               | NULL       |
| 192.168.70.73 | 3306 | 1469635702416062 | 542               | NULL       |
+---------------+------+------------------+-------------------+------------+
6 rows in set (0.00 sec)

The previous examples show that ProxySQL is able to connect and ping the nodes you have added.

To enable monitoring of these nodes, load them at runtime:

mysql@proxysql> LOAD MYSQL SERVERS TO RUNTIME;

Create ProxySQL client user¶

ProxySQL must have users that can access backend nodes to manage connections.

To add a user, insert credentials into mysql_users table:

mysql@proxysql> INSERT INTO mysql_users (username,password) VALUES ('sbuser','sbpass');

Expected output

Query OK, 1 row affected (0.00 sec)

Note

ProxySQL currently doesn’t encrypt passwords.

Load the user into runtime space and save these changes to disk (ensuring that they persist after ProxySQL shuts down):

mysql@proxysql> LOAD MYSQL USERS TO RUNTIME;
mysql@proxysql> SAVE MYSQL USERS TO DISK;

To confirm that the user has been set up correctly, you can try to log in as root:

root@proxysql:~# mysql -u sbuser -psbpass -h 127.0.0.1 -P 6033

Expected output

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1491
Server version: 5.5.30 (ProxySQL)

Copyright (c) 2009-2020 Percona LLC and/or its affiliates
Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

To provide read/write access to the cluster for ProxySQL, add this user on one of the Percona XtraDB Cluster nodes:

mysql@pxc3> CREATE USER 'sbuser'@'192.168.70.74' IDENTIFIED BY 'sbpass';

Expected output

Query OK, 0 rows affected (0.01 sec)

mysql@pxc3> GRANT ALL ON *.* TO 'sbuser'@'192.168.70.74';

Expected output

Query OK, 0 rows affected (0.00 sec)

Test cluster with sysbench¶

You can install sysbench from Percona software repositories:

For Debian or Ubuntu:

root@proxysql:~# apt install sysbench

For Red Hat Enterprise Linux or CentOS

root@proxysql:~# yum install sysbench

Note

sysbench requires ProxySQL client user credentials that you created in Creating ProxySQL Client User.

Create the database that will be used for testing on one of the Percona XtraDB Cluster nodes:
```
mysql@pxc1> CREATE DATABASE sbtest;
```

Populate the table with data for the benchmark on the ProxySQL node:

root@proxysql:~# sysbench --report-interval=5 --num-threads=4 \
--num-requests=0 --max-time=20 \
--test=/usr/share/doc/sysbench/tests/db/oltp.lua \
--mysql-user='sbuser' --mysql-password='sbpass' \
--oltp-table-size=10000 --mysql-host=127.0.0.1 --mysql-port=6033 \
prepare

Run the benchmark on the ProxySQL node:

root@proxysql:~# sysbench --report-interval=5 --num-threads=4 \
--num-requests=0 --max-time=20 \
--test=/usr/share/doc/sysbench/tests/db/oltp.lua \
--mysql-user='sbuser' --mysql-password='sbpass' \
--oltp-table-size=10000 --mysql-host=127.0.0.1 --mysql-port=6033 \
run

ProxySQL stores collected data in the stats schema:

mysql@proxysql> SHOW TABLES FROM stats;

Expected output

+--------------------------------+
| tables                         |
+--------------------------------+
| stats_mysql_query_rules        |
| stats_mysql_commands_counters  |
| stats_mysql_processlist        |
| stats_mysql_connection_pool    |
| stats_mysql_query_digest       |
| stats_mysql_query_digest_reset |
| stats_mysql_global             |
+--------------------------------+

For example, to see the number of commands that run on the cluster:

mysql@proxysql> SELECT * FROM stats_mysql_commands_counters;

Expected output

+---------------------------+---------------+-----------+-----------+-----------+---------+---------+----------+----------+-----------+-----------+--------+--------+---------+----------+
| 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 |
+---------------------------+---------------+-----------+-----------+-----------+---------+---------+----------+----------+-----------+-----------+--------+--------+---------+----------+
| ALTER_TABLE               | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| ANALYZE_TABLE             | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| BEGIN                     | 2212625       | 3686      | 55        | 2162      | 899     | 569     | 1        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| CHANGE_REPLICATION_SOURCE | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| COMMIT                    | 21522591      | 3628      | 0         | 0         | 0       | 1765    | 1590     | 272      | 1         | 0         | 0      | 0      | 0       | 0        |
| CREATE_DATABASE           | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| CREATE_INDEX              | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
...
| DELETE                    | 2904130       | 3670      | 35        | 1546      | 1346    | 723     | 19       | 1        | 0         | 0         | 0      | 0      | 0       | 0        |
| DESCRIBE                  | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
...
| INSERT                    | 19531649      | 3660      | 39        | 1588      | 1292    | 723     | 12       | 2        | 0         | 1         | 0      | 1      | 2       | 0        |
...
| SELECT                    | 35049794      | 51605     | 501       | 26180     | 16606   | 8241    | 70       | 3        | 4         | 0         | 0      | 0      | 0       | 0        |
| SELECT_FOR_UPDATE         | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
...
| UPDATE                    | 6402302       | 7367      | 75        | 2503      | 3020    | 1743    | 23       | 3        | 0         | 0         | 0      | 0      | 0       | 0        |
| USE                       | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
| SHOW                      | 19691         | 2         | 0         | 0         | 0       | 0       | 1        | 1        | 0         | 0         | 0      | 0      | 0       | 0        |
| UNKNOWN                   | 0             | 0         | 0         | 0         | 0       | 0       | 0        | 0        | 0         | 0         | 0      | 0      | 0       | 0        |
+---------------------------+---------------+-----------+-----------+-----------+---------+---------+----------+----------+-----------+-----------+--------+--------+---------+----------+
45 rows in set (0.00 sec)

Automatic failover¶

ProxySQL will automatically detect if a node is not available or not synced with the cluster.

You can check the status of all available nodes by running:

mysql@proxysql> SELECT hostgroup_id,hostname,port,status FROM runtime_mysql_servers;

The following output shows the status of all available nodes:

Expected output

+--------------+---------------+------+--------+
| hostgroup_id | hostname      | port | status |
+--------------+---------------+------+--------+
| 0            | 192.168.70.71 | 3306 | ONLINE |
| 0            | 192.168.70.72 | 3306 | ONLINE |
| 0            | 192.168.70.73 | 3306 | ONLINE |
+--------------+---------------+------+--------+
3 rows in set (0.00 sec)

To test problem detection and fail-over mechanism, shut down Node 3:

root@pxc3:~# service mysql stop

ProxySQL will detect that the node is down and update its status to OFFLINE_SOFT:

mysql@proxysql> SELECT hostgroup_id,hostname,port,status FROM runtime_mysql_servers;

Expected output

+--------------+---------------+------+--------------+
| hostgroup_id | hostname      | port | status       |
+--------------+---------------+------+--------------+
| 0            | 192.168.70.71 | 3306 | ONLINE       |
| 0            | 192.168.70.72 | 3306 | ONLINE       |
| 0            | 192.168.70.73 | 3306 | OFFLINE_SOFT |
+--------------+---------------+------+--------------+
3 rows in set (0.00 sec)

Now start Node 3 again:

root@pxc3:~# service mysql start

The script will detect the change and mark the node as ONLINE:

mysql@proxysql> SELECT hostgroup_id,hostname,port,status FROM runtime_mysql_servers;

Expected output

+--------------+---------------+------+--------+
| hostgroup_id | hostname      | port | status |
+--------------+---------------+------+--------+
| 0            | 192.168.70.71 | 3306 | ONLINE |
| 0            | 192.168.70.72 | 3306 | ONLINE |
| 0            | 192.168.70.73 | 3306 | ONLINE |
+--------------+---------------+------+--------+
3 rows in set (0.00 sec)

Assisted maintenance mode¶

Usually, to take a node down for maintenance, you need to identify that node, update its status in ProxySQL to OFFLINE_SOFT, wait for ProxySQL to divert traffic from this node, and then initiate the shutdown or perform maintenance tasks. Percona XtraDB Cluster includes a special maintenance mode for nodes that enables you to take a node down without adjusting ProxySQL manually.

Initiating pxc_maint_mode=MAINTENANCE does not disconnect existing connections. You must terminate these connections by either running your application code or forcing a re-connection. With a re-connection, the new connections are re-routed around the PXC node in MAINTENANCE mode.

Assisted maintenance mode is controlled via the pxc_maint_mode variable, which is monitored by ProxySQL and can be set to one of the following values:

DISABLED: This value is the default state that tells ProxySQL to route traffic to the node as usual.
SHUTDOWN: This state is set automatically when you initiate node shutdown.

You may need to shut down a node when upgrading the OS, adding resources, changing hardware parts, relocating the server, etc.

When you initiate node shutdown, Percona XtraDB Cluster does not send the signal immediately. Intead, it changes the state to pxc_maint_mode=SHUTDOWN and waits for a predefined period (10 seconds by default). When ProxySQL detects that the mode is set to SHUTDOWN, it changes the status of this node to OFFLINE_SOFT. This status stops creating new node connections. After the transition period, long-running active transactions are aborted.
MAINTENANCE: You can change to this state if you need to perform maintenance on a node without shutting it down.

You may need to isolate the node for a specific time so that it does not receive traffic from ProxySQL while you resize the buffer pool, truncate the undo log, defragment, or check disks, etc.

To do this, manually set pxc_maint_mode=MAINTENANCE. Control is not returned to the user for a predefined period (10 seconds by default). You can increase the transition period using the pxc_maint_transition_period variable to accommodate long-running transactions. If the period is long enough for all transactions to finish, there should be little disruption in the cluster workload. If you increase the transition period, the packaging script may determine the wait as a server stall.

When ProxySQL detects that the mode is set to MAINTENANCE, it stops routing traffic to the node. During the transition period, any existing connections continue, but ProxySQL avoids opening new connections and starting transactions. Still, the user can open connections to monitor status.

Once control is returned, you can perform maintenance activity.

Note

Data changes continue to be replicated across the cluster.

After you finish maintenance, set the mode back to DISABLED. When ProxySQL detects this, it starts routing traffic to the node again.

Related sections

Setting up a testing environment with ProxySQL

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Last update: 2023-07-21