Patroni

A majority of members must agree before a decision stands, which is what stops two halves of a partitioned cluster both acting as leader.

Two nodes both believe they are primary, usually after a network partition, and both accept writes that cannot afterwards be reconciled.

Positively preventing a demoted or unreachable node from continuing to serve, rather than assuming it has stopped.

The delay between a write committing on the primary and becoming visible on a replica.