referee is a Postgres Pro Enterprise extension for managing quorum settings in clusters with an even number of nodes configured with multimaster. Installed on a separate system, the referee extension provides a voting node to assign the quorum status to a subset of nodes if only half of the cluster nodes remain connected to each other.

If a multi-master cluster is split into equal parts, or half of the cluster nodes fail, each subset of nodes that equals half of the cluster tries to access the referee. The first subset that gets connected to the referee wins the voting and continues working, while all the other nodes are excluded from the cluster to avoid split-brain problems.

The referee node does not store any cluster data, so it is very lightweight and can be located on systems with limited resources. For details on how to set up and use a referee node with multimaster, see Section F.36.3.3.