Manual:$wgLBFactoryConf/en

Details
To set up a multi-primary (formerly called multi-master) wiki farm, set the class here to something that can return a with an appropriate primary on a call to. The class identified here is responsible for reading,  , etc., so overriding it may cause those globals to be ignored.

The class is provided for this purpose, the configuration for this class is provided below:


 * sectionsByDB
 * A map of database names to section names


 * sectionLoads
 * A 2-d map. For each section, gives a map of server names to load ratios. For example:


 * serverTemplate
 * A server info associative array as documented for . The host, hostName and load entries will be overridden.


 * groupLoadsBySection
 * A 3-d map giving server load ratios for each section and group. For example:


 * groupLoadsByDB
 * A 3-d map giving server load ratios by DB name.


 * hostsByName
 * A map of hostname to IP address.


 * externalLoads
 * A map of external storage cluster name to server load map


 * externalTemplate
 * A server info structure used for external storage servers


 * templateOverridesByServer
 * A 2-d map overriding mainTemplate or externalTemplate on a server-by-server basis.


 * templateOverridesByCluster
 * A 2-d map overriding externalTemplate by cluster


 * masterTemplateOverrides
 * An override array for mainTemplate and externalTemplate for all primary servers.

3 wikis all using localhost as db server
Here is how a simple configuration would work, where you have three wikis (wikidb1, wikidb2 and wikidb3), all of which using the same database server (but with different database names), and all of them having a single primary server which is the same as your webserver (localhost)

3 wikis using different hosts as db and one replica database
Say your wiki has grown a bit. Lets say you want to separate your db server from your webserver. And you have a replica server for which you have set up replication. And you now put wikidb3 on an entirely separate server.

So say we have wikidb1 and wikidb2 share a primary server (db1) and a replica (db2). Wikidb3 has its own db server db3 (and no replica). You would do something like:

Wikimedia configuration
To see how Wikimedia uses  to configure its wikis see:


 * db-eqiad.php

Wikimedia configuration uses also.