From: | Benoit Lobréau <benoit(dot)lobreau(at)gmail(dot)com> |
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To: | pgsql-general(at)postgresql(dot)org |
Subject: | clarification about standby promotion |
Date: | 2017-02-08 17:53:24 |
Message-ID: | CAPE8EZ5NUH4G2Z7M4TMhLghGGDDot0cb4c9vz+vH75i-ME5Tig@mail.gmail.com |
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Lists: | pgsql-general |
Hi,
I would like to clarify something about standby promotion. From the
sentence below. I understand that, during the promotion process, postgres
will replay all the available wals (from the archive or pg_xlog).
https://www.postgresql.org/docs/9.5/static/warm-standby.html#STREAMING-REPLICATION
25.2.2. Standby Server Operation
...
Standby mode is exited and the server switches to normal operation when
pg_ctl promote is run or a trigger file is found (trigger_file). Before
failover, any WAL immediately available in the archive or in pg_xlog will
be restored, but no attempt is made to connect to the master.
I have seen several articles like this one (
https://www.enterprisedb.com/switchoverswitchback-postgresql-93) where they
say that pg_last_xlog_receive_location() and pg_last_xlog_replay_location()
should be checked before promotion. I don't understand why since they will
be replayed anyway. Did something changed since 9.3 about this ?
Thanks for you help. please excuse my poor english.
Benoit
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