In some of our projects we use Percona Server instead of MySQL database, with splited Write / read nodes. Doctrine has an excelent built-in solution to handle such situation wich is supported by Symfony 2
This class enable us to define master node, and one or more slaves nodes. By default SELECT queries are made using one of slaves, and other operations (INSERT, UPDATE, DELETE) made via master.
But the class has few limitations, which we should remember, espacially second point:
- Master picked when ‘exec’, ‘executeUpdate’, ‘insert’, ‘delete’, ‘update’, ‘createSavepoint’, ‘releaseSavepoint’, ‘beginTransaction’, ‘rollback’, ‘commit’, ‘query’ or ‘prepare’ is called.
- If master was picked once during the lifetime of the connection it will always get picked afterwards.
More about the class in Doctrine documentation
According to these we were a little bit worried that to much queries will go to master. But in our tests with quite complex application, we have about 99,8% queries go to slaves nodes, which is great result for us.
Configure Doctrine MasterSlaveConnection in Symfony 2
We must configure using slaves in doctrine section in our Symfony 2 config.yml
Only one connection
If we have only one connection in our doctrine config (default)
doctrine: dbal: driver: %database_driver% host: %database_host% port: %database_port% dbname: %database_name% user: %database_user% password: %database_password% charset: UTF8 slaves: slave1: dbname: %database_slave1_name% host: %database_slave1_host% port: %database_slave1_port% user: %database_slave1_user% password: %database_slave1_password% slave2: dbname: %database_slave2_name% host: %database_slave2_host% port: %database_slave2_port% user: %database_slave2_user% password: %database_slave2_password%
Using few connections
If we have more the one connection in our doctrine config, using connections section.
doctrine: dbal: default_connection: default connections: default: driver: "%database_driver%" host: "%database_host%" port: "%database_port%" dbname: "%database_name%" user: "%database_user%" password: "%database_password%" charset: UTF8 slaves: slave1: dbname: "%database_name%" host: "%database_host%" port: "%database_slave1_port%" user: "%database_user%" password: "%database_password%" charset: UTF8 slave2: dbname: "%database_name%" host: "%database_host%" port: "%database_slave2_port%" user: "%database_user%" password: "%database_password%" charset: UTF8
We use HAProxy for defining nodes, so the nodes differs in our configuration only by port.
Alternative master-slave solutions
Override doctrine classes
There is an easy way to override Doctrine Doctrine_Query and Doctrine_Record classes to implement own logic, how doctrine should choose connections.
External application – MySQL Proxy
We could use external application, which will work as proxy server. Our app will be connect to proxy, and the proxy will balance to master or slaves server.
For MySQL/Percona there is Mysql Proxy https://dev.mysql.com/downloads/mysql-proxy/ currently still in alpha.