README

A Magento 2 module that implements automatic read/write database splitting. Read queries are distributed across multiple read replicas using round-robin selection, while write operations always go to the master database. CLI operations (indexing, cron, console commands) always use the master to avoid temporary table conflicts. We ensure a 'writer first' approach and include a writer fallback for defensive posturing. It is built to support multiple readers, but 1 will work just as well.

Configuration

Add reader connection configurations to app/etc/env.php:

'db' => [
    'connection' => [
        'default' => [
            'host' => 'master-db-host',
            'dbname' => 'magento',
            'username' => 'dbuser',
            'password' => 'dbpass',
            'model' => 'mysql4',
            'engine' => 'innodb',
            'initStatements' => 'SET NAMES utf8;',
            'active' => '1',
            'driver_options' => [
                1014 => false
            ]
        ],
        'indexer' => [
            'host' => 'master-db-host',
            'dbname' => 'magento',
            'username' => 'dbuser',
            'password' => 'dbpass',
            'model' => 'mysql4',
            'engine' => 'innodb',
            'initStatements' => 'SET NAMES utf8;',
            'active' => '1'
        ]
    ],
    'reader_connections' => [
        'default' => [
            // Note this is an array, even if only using 1 you must keep this structure
            [
                'host' => 'reader-1-host',
                'dbname' => 'magento',
                'username' => 'dbuser',
                'password' => 'dbpass',
                'model' => 'mysql4',
                'engine' => 'innodb',
                'initStatements' => 'SET NAMES utf8;',
                'active' => '1',
                'driver_options' => [
                    1014 => false
                ]
            ],
            [
                'host' => 'reader-2-host',
                'dbname' => 'magento',
                'username' => 'dbuser',
                'password' => 'dbpass',
                'model' => 'mysql4',
                'engine' => 'innodb',
                'initStatements' => 'SET NAMES utf8;',
                'active' => '1',
                'driver_options' => [
                    1014 => false
                ]
            ]
        ]
    ]
],

How It Works

• SELECT, SHOW, DESCRIBE, EXPLAIN queries are routed to reader connections
• INSERT, UPDATE, DELETE, DDL, and transaction queries go to master
• Queries within transactions always use master for consistency
• CLI operations (bin/magento commands) always use master
• Failed reader connections automatically fall back to master
• Round-robin load balancing across active readers

Disabling Readers

Set 'active' => '0' for any reader connection to temporarily disable it without removing the configuration.

Requirements

• PHP 8.0 or higher
• Magento 2.4+
• MySQL master-slave replication configured
• Read replicas must be in sync with master

Notes

The indexer connection is never split and always uses the master database to avoid issues with temporary tables during reindexing operations.