From: | "Bossart, Nathan" <bossartn(at)amazon(dot)com> |
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To: | Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, Bernd Helmle <mailings(at)oopsware(dot)de>, Michael Paquier <michael(at)paquier(dot)xyz>, "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: A few new options for CHECKPOINT |
Date: | 2020-11-30 17:17:41 |
Message-ID: | 3785B778-9FED-43DF-B543-64FC88A35823@amazon.com |
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Lists: | pgsql-hackers |
On 11/29/20, 7:21 PM, "Stephen Frost" <sfrost(at)snowman(dot)net> wrote:
> Checkpoints are always happening though, that's kind of my point..?
> Sure, you get lucky sometimes that the time you snapshot might have less
> outstanding WAL than at some other time, but I'm not convinced that this
> patch is really going to give a given user that much reduced amount of
> WAL that has to be replayed more than just randomly timing the
> snapshot, and if it's not clearly better, always, then I don't think we
> can reasonably document it as such or imply that this is how folks
> should implement snapshot-based backups.
I see your point. Using a non-immediate checkpoint might help you
keep your recovery time slightly more consistent, but you're right
that it's likely not going to be a dramatic improvement. Your
recovery time will be 1 minute versus 1-2 minutes or 2 minutes versus
2-4 minutes, not 3 seconds versus 5 minutes.
> Did you have other concrete examples that we could reference as to when
> it would be useful to use these options?
I don't have any at the moment. I figured that if we're going to
allow users to manually trigger checkpoints, we might as well allow
them to configure it to avoid things like IO spikes.
Nathan
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