The autoslave_affected_tables will always be read from the master. In case "global replication lag" is turned on, this will cause every single request to Drupal to open at least a connection to the master database.
It is possible to use MemCache or MongoDB for this storage instead, by using the "affected tables backend" option:
<?php
// Tell AutoSlave where the MongoDB module lives
$conf['autoslave_mongodb_module'] = 'sites/all/modules/contrib/mongodb';
$databases['default']['default'] = array (
'driver'=> 'autoslave',
'master'=> array('master'),
'slave'=> array('slave'),
// Use one of the following three
'affected tables backend'=> 'autoslave.affected_tables.db.inc', // Default
'affected tables backend'=> 'autoslave.affected_tables.mongo.inc',
'affected tables backend'=> 'autoslave.affected_tables.memcache.inc',
);
?>The above obviously requires that the MongoDB module is present and properly configured including a MongoDB server running.
MongoDB is the recommended choice of weapon here because of its speed and persistent data. If using the DB backend, AutoSlave will ALWAYS make a connection to the master database and read the list of tables from there. If the number of connections to the master database is a concern you should probably opt for MongoDB or MemCache here.
Be aware, that using memcache can cause problems since it inherently does not persist its data. To mitigate this, use a different memcache daemon for this purpose to avoid unwanted flushes. AutoSlave uses the cache bin "autoslave_affected_tables" and you configure memcache as usual for this bin.
