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MySQL master slave configuration

Is vanilla providing support to make use of MySQL master slave configuration? Kindly confirm.


  • The framework is agnostic towards any replication arrangement of the database and therefore doesn't provide config for this. Suggest using a proxy for high availability reads.

    grep is your friend.

  • I believe there's actually a config setting that uses a different database connection for all SELECT queries:

    $Configuration['Database']['Slave']['Name'] = '';
    $Configuration['Database']['Slave']['Host'] = '';
    $Configuration['Database']['Slave']['User'] = '';
    $Configuration['Database']['Slave']['Password'] = '';

    No idea, if it works though.

  • LincLinc Detroit Admin

    We've never used this database setup. It may work. If you identify a specific problem, we'd likely accept a pull request to patch it. A bug report of this configuration simply not working is likely to be ignored, however. It's not a priority for us.

    If you're experiencing heavy READ db traffic, I suggest investigating Varnish instead.

  • I think a proxy would be a better approach especially for high availability and redundancy. Separation of concerns. A framework shouldn't be concerned about database replication IMO.

    grep is your friend.

  • Thanks for your inputs.

    @Linc @x00

    But I am bit curious, as seems like some "Slave" configuration support is being available as mentioned by @Bleistivt

    So can you please confirm.

    Can we make use of these configs setting for using slave db connection?

    $Configuration['Database']['Slave']['Name'] = '';
    $Configuration['Database']['Slave']['Host'] = '';
    $Configuration['Database']['Slave']['User'] = '';
    $Configuration['Database']['Slave']['Password'] = '';

  • x00x00 MVP
    edited August 2018

    nobody responding has used the setup you would have to try. I would still recommend a proxy, becuase it abstracts that functionality out form the framework and will be more flexible, e.g muliple slaves.

    grep is your friend.

  • R_JR_J Ex-Fanboy Munich Admin

    Look at the classes Gdn_Database, PostController and the CommentModel. The PostController and the CommentModel both use ['Slave' => false] as options in some queries in order to force this queries to be made against the master database.

    In the Gdn_Database you find:

    $config = Gdn::config('Database');


            if (array_key_exists('Slave', $config)) {
                $this->_SlaveConfig = $config['Slave'];

    Therefore the keys bleistivt mentioned are correct.

    The database class has a method which returns the normal connection if there is no slave configured, but if there is a config for a slave db, a connection to the slave is returned.

    In the query() method, you can find the following code:

            // We will retry this query a few times if it fails.
            $tries = $this->ConnectRetries + 1;
            if ($tries < 1) {
                $tries = 1;
            for ($try = 0; $try < $tries; $try++) {
                if (val('Type', $options) == 'select' && val('Slave', $options, null) !== false) {
                    $pDO = $this->slave();
                    $this->LastInfo['connection'] = 'slave';
                } else {
                    $pDO = $this->connection();
                    $this->LastInfo['connection'] = 'master';

    As you can see, if there is no dedicated ['Slave' => false] option in the query, the query is run against the connection returned by the slave() method (which is Slave if there is a slave or Master if there is no slave)

    Therefore I'm quite sure that this Slave config parameters will work. But the ['Slave' => false] is used very sparsely and how it is used, I do not expect any performance wins on using such a setup (I'm no db expert, though)

  • LincLinc Detroit Admin

    @R_J said:
    But the ['Slave' => false] is used very sparsely and how it is used, I do not expect any performance wins on using such a setup

    That's my take as well. We probably added it pre-v1 and have never actually made a concerted effort to continue implementing it once we realized it wasn't necessary. I'd be more inclined to remove it than improve it.

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