Question

I am having trouble getting Drupal 7.7 to use a MySQL slave database.

My settings.php is as follows:

$databases['default']['default'] = array(
  'driver' => 'mysql',
  'database' => 'my_db',
  'username' => 'dbuser',
  'password' => 'dbpw',
  'host' => 'db-ip-address'
);
$databases['default']['slave'][] = array(
  'driver' => 'mysql',
  'database' => 'my_db',
  'username' => 'dbuser',
  'password' => 'dbpw',
  'host' => '127.0.0.1'
);

Replication itself is working great. When I add new content to the site it quickly is replicated on the slave.

Looking at tcpdump though, I never see a call to the local database.

Is there anything I’m missing to enable Drupal to use the slave?

Answer 1

Using slave databases is barely implemented in Drupal core. If you are developing your own modules then calls to db_query need to specify that they want to use the slave database using the $options array. See DatabaseConnection::defaultOptions for how to set this array.