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Re: checkpoint_timout with no WAL activity - Mailing list pgsql-general

From Tom DalPozzo
Subject Re: checkpoint_timout with no WAL activity
Date
Msg-id CAK77FCT2Rbs4MbTDa9R8RxXnMx4=o_S48_tbcL=Z_9=wa9Wmmg@mail.gmail.com
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In response to Re: checkpoint_timout with no WAL activity  (Michael Paquier <michael.paquier@gmail.com>)
Responses Re: checkpoint_timout with no WAL activity  (Michael Paquier <michael.paquier@gmail.com>)
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I'm using 9.5.3 . I had read about that bug but I didn't know that wal_level=archive is equivalent to hot_standby from this point of view! I guess it's equivalent in 9.5.3 too.
Regards
Pupillo




2016-11-07 13:26 GMT+01:00 Michael Paquier <michael.paquier@gmail.com>:
On Mon, Nov 7, 2016 at 9:21 PM, Tom DalPozzo <t.dalpozzo@gmail.com> wrote:
> I know that, but with neither database activity or chekpoint, it doesn't
> force anything. The fact is that there are checkpoints being executed every
> checkpoint_timeout, and I don't understand why as if no WAL has been written
> we should not care about passing the timeout.

You may want to look at that:
https://www.postgresql.org/message-id/20151016203031.3019.72930@wrigleys.postgresql.org
And the patches on this thread to fix the checkpoint skip logic:
https://www.postgresql.org/message-id/flat/CAB7nPqQcPqxEM3S735Bd2RzApNqSNJVietAC=6kfkYv_45dKwA@mail.gmail.com#CAB7nPqQcPqxEM3S735Bd2RzApNqSNJVietAC=6kfkYv_45dKwA@mail.gmail.com

My guess is that you are using 9.6 because wal_level = archive is
equivalent to hot_standby, and the checkpoint skip logic is broken
because of standby snapshots happening in the bgwriter...
--
Michael

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