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Re: Trigger file behavior with the standby - Mailing list pgsql-hackers

From Keiko Oda
Subject Re: Trigger file behavior with the standby
Date
Msg-id CAFVgSmYyiknHHUtNCxeu_xOJo7CjyPrV9S3vzWB7k+qyLUR2Ng@mail.gmail.com
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In response to Re: Trigger file behavior with the standby  (Michael Paquier <michael@paquier.xyz>)
Responses Re: Trigger file behavior with the standby  (Michael Paquier <michael@paquier.xyz>)
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Thanks a lot for the answer, Michael (and sorry for the slow response)!

So, if I understand what you're saying correctly, I'm seeing this behavior because wal-e keeps fetching wal files from s3 regardless of this trigger_file, and these fetched wal files are in pg_wal (or pg_xlog), therefore Postgres just tries to restore whatever available in pg_wal before the failover. Or, even if there is no file in pg_wal, it still tries to fetch from the "archive" (s3).
In other words, if I would like to do "immediate failover" (and do not care about WAL files available in archive or in pg_wal), I should be tweaking restore_command so that no further fetching/restoring happens.
Is it... accurate?

Thanks,
Keiko

On Mon, Mar 19, 2018 at 9:28 PM, Michael Paquier <michael@paquier.xyz> wrote:
On Mon, Mar 19, 2018 at 01:27:21PM -0700, Keiko Oda wrote:
> I'm seeing the following behavior with a trigger file which is very
> confusing to me, I'd like to get some advice of what is the expected
> behavior of the trigger file with the standby.

This portion from the docs includes your answer:
https://www.postgresql.org/docs/devel/static/warm-standby.html#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_wal will
be restored, but no attempt is made to connect to the master.

So when creating a trigger file or signaling for promotion, any WAL
files available are first fetched, and then promotion happens.  In your
case all the WAL segments from the archives are retrieved first.
--
Michael

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