> On 29 Oct 2015, at 14:39, Vladimir Borodin <r...@simply.name> wrote: > > f I understand right, with hot_standby_feedback = on standby tells the master > xmin of the earliest transaction on standby. And autovacuum worker on master > takes it into account when doing vacuum cleanup (because it can see it from > pg_replications_slots view), AFAIK with GetOldestXmin function. But I don’t > understand why with READ COMMITED transactions xmin in pg_replication_slots > view on master continues to increase while with REPEATABLE READ xmin freezes > until this transaction finishes.
Could it be a consequence of how REPEATABLE READ transactions handle snapshots? With REPEATABLE READ the snapshot is acquired only once at the beginning of a transaction; a READ COMMITTED transaction re-evaluates its snapshot with each new command. http://www.postgresql.org/docs/current/static/transaction-iso.html Kind regards, -- Oleksii
