Re: should we enable log_checkpoints out of the box?

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От Nikolay Samokhvalov
Тема Re: should we enable log_checkpoints out of the box?
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Msg-id CANNMO+JfQu+Rk0_p9doU+de3B6BDOp2rDap--fuovDv=5WVkQQ@mail.gmail.com
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Ответ на Re: should we enable log_checkpoints out of the box?  (Robert Haas <robertmhaas@gmail.com>)
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On Tue, Nov 2, 2021 at 11:50 AM Robert Haas <robertmhaas@gmail.com> wrote:
I almost proposed 1m rather than 10m, but then I thought the better of
it. I think it's unlikely that an autovacuum that takes 1 minute is
really the cause of some big problem you're having on your system.
Typical problem cases I see are hours or days long, so even 10 minutes
is pretty short.

I'm talking about the autoANALYZE part, not VACUUM. In my case, it was a few tables
~100GB-1TB in size, with 1-2 GIN indexes (with fastupdate, default pending list size limit, 4MB),
10 workers with quite high bar in terms of throttling. And default_statistics_target = 1000.
Observed autoANALYZE timing reached dozens of minutes, sometimes ~1 hour for a table.
The problem is that, it looks, ANALYZE (unlike VACUUM) holds snapshot, takes XID -- and it 
all leads to the issues on standbys, if it takes so long. I'm going to post the findings in a separate
thread, but the point is that autoANALYZE running minutes *may* cause big performance issues.
That's why 1m seems a good threshold to me, even if leads to having 3 log entries per minute from
3 workers. It's a quite low log traffic, but the data there is really useful for retrospective analysis.

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