$db['expressionengine']['cachedir'] - what does it do?

Question

I have searched Ellis Labs docs, but I can't find any details about the $db['expressionengine']['cachedir'] setting in the database.php config file.

I recently 'fixed' this value (it was pointing to a non-existent directory) as an EE 2.8 site was running very slowly, but this caused problems for a custom plugin that inserts new channel entries by duplicating an existing entry and adding some new field values to the new entry, I'd like to understand how correcting this value caused this.

Also what effects will it actually have on a site if this value is incorrect?

Presumably it's related to $db['expressionengine']['cache_on'] (also in the database.php config file)?

Is it related to $config['enable_db_caching'] in config.php?

Answer 1

It is used by the CodeIgniter database drivers. $db['expressionengine']['cache_on'] is exactly what it is related to. The $db['expressionengine'] settings are passed to CodeIgniter and read based on the active record group set $active_group = 'expressionengine';.

CodeIgniter 2.x Database Configuration

Answer 2

As far as I can tell it's not actually used for anything. Tried searching the source for 'cachedir' and I see it is set numerous places but never used.

In DB_Driver.php there is this function, which is never actually called from anywhere:

/**
 * Set Cache Directory Path
 *
 * @access  public
 * @param   string  the path to the cache directory
 * @return  void
 */
function cache_set_path($path = '')
{
    // Query caching now uses caching drivers
    ee()->load->library('logger');
    ee()->logger->deprecated('2.8');

    $this->cachedir = $path;
}

Notice the logger->deprecated('2.8') call there. So my guess is that this is some legacy code from the good old days.