Using database replication with Pressflow 5 and 6

Configuring settings.php

For an unnamed master connection and a single slave database

$db_url = 'mysqli://user:password@master-host/database';

$db_slave_url = 'mysqli://user:password@slave-host/database';

For an unnamed master connection and multiple slave databases

$db_url = 'mysqli://user:password@master-host/database';

$db_slave_url = array();
$db_slave_url[] = 'mysqli://user:password@slave-host-1/database';
$db_slave_url[] = 'mysqli://user:password@slave-host-2/database';

For a named master connection and a single slave database

$db_url = array();
$db_url['default'] = 'mysqli://user:password@master-host/database';
$db_url['another'] = 'mysqli://user:password@another-host/another-database';

$db_slave_url = array();
$db_slave_url['default'] = 'mysqli://user:password@slave-host/database';

For a named master connection and multiple slave databases

$db_url = array();
$db_url['default'] = 'mysqli://user:password@master-host/database';
$db_url['another'] = 'mysqli://user:password@another-host/database';

$db_slave_url = array();
$db_slave_url['default'] = array();
$db_slave_url['default'][] 'mysqli://user:password@slave-host-1/database';
$db_slave_url['default'][] 'mysqli://user:password@slave-host-2/database';

Using the Cookie Cache Bypass module

The Cookie Cache Bypass module allows anonymous users who have submitted forms to bypass reverse proxy caches and database replication to get fresh pages, presumably containing results of their form postings. This module works by adding an additional #submit handler to all form submissions that generates a short-lived cookie. This cookie persists long enough that, by the time of its expiration, slave databases and reverse proxy caches should be updated with that user's action.

Use of this module is important in situations that use reverse proxy caching or database replication in combination with anonymous user activity. Without this module enabled, anonymous users may post comments but be unable to immediately see their work. This causes frustration and unnecessary resubmission.

API: Sending queries to the slave servers

Pressflow's replication functionality add two main functions to the API and modifies a third.

• db_query_slave
  • This function is parameter-equivalent to db_query, but should only be used with SELECT queries that operate properly with slightly stale data.
• db_query_range_slave
  • This function is parameter-equivalent to db_query_range with the same caveats as db_query_slave.
• pager_query
  • Paginated queries are always sent to the slave(s).