>>>>> "S" == S Bob <sbob@xxxxxxxxxxxxxxxxxxxxx> writes: S> Hi all; S> Does PostgreSQL store a unique cluster or instance identifier that S> we can access to identify our instances? Yes. But it's not easy to get at: it's the "Database system identifier" shown in the output of pg_controldata. (pg12+ will have a function to get it from SQL, but released versions don't.) e.g. Database system identifier: 6659016342798875639 The number is mostly generated from the time the instance was created, with some bits modified. So for example: $ perl -le 'print scalar gmtime +(shift >> 32)' 6659016342798875639 Sun Feb 17 17:04:21 2019 PG uses this internally to make sure that replication never tries to apply WAL records generated on one system to a different system. Physical replication secondary systems share the primary's system identifier since they always originate as a copy (via base backup) of the primary. -- Andrew (irc:RhodiumToad)
