PostgreSQL 12 High Availability Cookbook - Third Edition

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These types of multi-master PostgreSQL clusters often require two direct connections between all participating nodes, one for each direction of communication. This is called a Mesh topology, and is considered by some to be a source of excessive communication overhead. If we think about it, that's a valid criticism given that every transaction in the cluster must eventually be acknowledged by every other primary node. In very active systems, the impact could be significant.

A scenario along the lines of the following diagram, for example, may present complications:

By merely adding three more primary nodes, we've increased the ...