Manual:$wgExternalServers/en

Details
An array of external MySQL servers.

collects all the usable clusters with all usable nodes of a cluster.

The top-level array's keys denote a cluster's name (The below example defines only one cluster. It has the name ).

The value to those keys are again arrays. They hold the specifications of the individual nodes, using the same format as $wgDBservers.

The first node is considered the master. All writes to the database are performed through this master node.

Zero or more slave nodes may follow. (In the example below, you find two slave nodes).

Each node should have its own,  ,  ,  , and  , as shown in the example. The  parameter allows to specify how much of the load should pass through this node.

e.g.

See External Storage for a discussion of this example, and how to turn this into a usable cluster configuration.