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This feature is also known as "quorum commit" especially in discussion on pgsql-hackers. This commit adds the following new syntaxes into synchronous_standby_names GUC. By using FIRST and ANY keywords, users can specify the method to choose synchronous standbys from the listed servers. FIRST num_sync (standby_name [, ...]) ANY num_sync (standby_name [, ...]) The keyword FIRST specifies a priority-based synchronous replication which was available also in 9.6 or before. This method makes transaction commits wait until their WAL records are replicated to num_sync synchronous standbys chosen based on their priorities. The keyword ANY specifies a quorum-based synchronous replication and makes transaction commits wait until their WAL records are replicated to *at least* num_sync listed standbys. In this method, the values of sync_state.pg_stat_replication for the listed standbys are reported as "quorum". The priority is still assigned to each standby, but not used in this method. The existing syntaxes having neither FIRST nor ANY keyword are still supported. They are the same as new syntax with FIRST keyword, i.e., a priorirty-based synchronous replication. Author: Masahiko Sawada Reviewed-By: Michael Paquier, Amit Kapila and me Discussion: <CAD21AoAACi9NeC_ecm+Vahm+MMA6nYh=Kqs3KB3np+MBOS_gZg@mail.gmail.com> Many thanks to the various individuals who were involved in discussing and developing this feature.
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