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?