Master/Slave configuration and use of slave connection

[gianstraf]

Preconditions (*)

1. Magento Commerce Edition ver. 2.4.2
2. PHP 7.4.6
3. Master/slave configuration

Steps to reproduce (*)

1. Add a slave connection with bin/magento setup:db-schema:add-slave

'db' => [
        'connection' => [
            'indexer' => [
                'host' => 'localhost',
                'dbname' => 'local_db2',
                'username' => 'local_user2',
                'password' => 'local_pass',
                'model' => 'mysql4',
                'engine' => 'innodb',
                'initStatements' => 'SET NAMES utf8;',
                'active' => '1',
                'persistent' => null
            ],
            'default' => [
                'host' => 'localhost',
                'dbname' => 'local_db2',
                'username' => 'local_user2',
                'password' => 'local_pass',
                'model' => 'mysql4',
                'engine' => 'innodb',
                'initStatements' => 'SET NAMES utf8;',
                'active' => '1',
                'driver_options' => [
                    1014 => false
                ]
            ]
        ],
        'table_prefix' => '',
        'slave_connection' => [
            'default' => [
                'host' => 'localhost',
                'dbname' => 'local_db2',
                'username' => 'local_user2_slave',
                'password' => 'local_pass',
                'maxAllowedLag' => '',
                'model' => 'mysql4',
                'engine' => 'innodb',
                'initStatements' => 'SET NAMES utf8;',
                'active' => '1'
            ]
        ]
    ],

2. Navigate on FE or BE or run a cli command: three different scenariuos

Expected result (*)

1. In case of CLI command, we expect that an export of products (for example), can work whole on slave database (all read operations). The master/slave configuration, is ignored (never used) in the CLI Context.
2. In case of BE operations (i.e. products list, sales order list), read queries should be ran on slave connection, lightening the master database.

Actual result (*)

1. Any command runned via CLI, "ignores" slave connection.
2. In case of BE operations (i.e. products list, sales order list) only a few queries are ran on slave database, the most are ran on master database. In the sales orders lists, in example, when framework save data on the "theme" table, all following queries go on the master connection, without return back to slave connection (a ratio of ~10% on the total, with the most of select statements on master database).

---

• Severity: S0 - Affects critical data or functionality and leaves users without workaround.
• Severity: S1 - Affects critical data or functionality and forces users to employ a workaround.
• Severity: S2 - Affects non-critical data or functionality and forces users to employ a workaround.
• Severity: S3 - Affects non-critical data or functionality and does not force users to employ a workaround.
• Severity: S4 - Affects aesthetics, professional look and feel, “quality” or “usability”.

[m2-assistant]

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[m2-assistant]

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[m2-assistant]

Hi @engcom-Lima. Thank you for working on this issue.
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• 4. Verify that the issue is reproducible on 2.4-develop branch

  Details

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[engcom-Lima]

Hi @gianstraf,

Can you please elaborate on Step 2. Once we do the Step1, It is incomplete like how to check the issue on BE or FE or even on CLI ?

[gianstraf]

Hi @gianstraf,

Can you please elaborate on Step 2. Once we do the Step1, It is incomplete like how to check the issue on BE or FE or even on CLI ?

@engcom-Lima, you can check the issue, for example enabling the log on mysql server:

SET global log_output = 'FILE';
SET global general_log_file='/tmp/mysql-all-queries-log';
SET global general_log = 1;

You can activate the log before any CLI command, and unactivate when command has ran.
Reading the log file, you will see that the only connection used is the master connection.

[engcom-Lima]

HI @gianstraf,

I understand your query but magento automatically regulates the connections to master or slave db & makes decisions based on the type of request and the required resources. Please read the info from documentation:

You can get detailed information on master/slave configurations and its use on:
https://devdocs.magento.com/guides/v2.4/performance-best-practices/advanced-setup.html
https://devdocs.magento.com/guides/v2.4/config-guide/multi-master/multi-master.html

All catalogue related queries go to main database. What you are asking can be marked as 'feature request' but I won't say it's a bug as Magento's architecture is like that.

Hope that clarifies.
Thanks