| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Bossart, Nathan" <bossartn(at)amazon(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, Bernd Helmle <mailings(at)oopsware(dot)de>, "tsunakawa(dot)takay(at)fujitsu(dot)com" <tsunakawa(dot)takay(at)fujitsu(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Change default of checkpoint_completion_target |
| Date: | 2021-01-15 21:51:56 |
| Message-ID: | 20210115215156.uuouk2u44gac6pts@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2020-12-08 12:41:35 -0500, Tom Lane wrote:
> FWIW, I kind of like the idea of getting rid of it completely.
> Is there really ever a good reason to set it to something different
> than that? If not, well, we have too many GUCs already, and each
> of them carries nonzero performance, documentation, and maintenance
> overhead.
I like the idea of getting rid of it too, but I think we should consider
evaluating the concrete hard-coded value a bit more careful than just
going for 0.9 based on some old recommendations in the docs. It not
being changeable afterwards...
I think it might be a good idea to immediately change the default to
0.9, and concurrently try to evaluate whether it's really the best value
(vs 0.95, 1 or ...).
FWIW I have seen a few cases in the past where setting the target to
something very small helped, but I think that was mostly because we
didn't yet tell the kernel to flush dirty data more aggressively.
Greetings,
Andres Freund
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