&gt; it&#x27;s a good CP system<p>PostgreSQL is not clustered by default so it is only <i>from the point of view of the theory</i> a CP system. Most <i>proper</i> CP systems have the ability to provide a limited form of Availability, which is, they are available in the majority partition (this is not &quot;A&quot; of CAP but is a lot better than, if primary is not available, the whole cluster is not available). If you use PostreSQL with asynchronous replication and a best-effort failover solution to provide some form of Availability, you are doing something that makes sense, assuming your product can tolerate the resulting weak consistency properties.<p>This is a great example on how CAP does not capture certain important semantics of a system. Technically a single primary node is CP but the real world CP systems have better availability than that, or they are useless (as CP systems).