From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Stephen Frost <sfrost(at)snowman(dot)net>, Sokolov Yura <funny(dot)falcon(at)postgrespro(dot)ru>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, pgsql-hackers-owner(at)postgresql(dot)org |
Subject: | Re: Increase Vacuum ring buffer. |
Date: | 2017-07-20 19:51:59 |
Message-ID: | 12790.1500580319@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I think that's a valid point. There are also other concerns here -
> e.g. whether instead of adopting the patch as proposed we ought to (a)
> use some smaller size, or (b) keep the size as-is but reduce the
> maximum fraction of shared_buffers that can be consumed, or (c) divide
> the ring buffer size through by autovacuum_max_workers. Personally,
> of those approaches, I favor (b). I think a 16MB ring buffer is
> probably just fine if you've got 8GB of shared_buffers but I'm
> skeptical about it when you've got 128MB of shared_buffers.
WFM. I agree with *not* dividing the basic ring buffer size by
autovacuum_max_workers. If you have allocated more AV workers, I think
you expect AV to go faster, not for the workers to start fighting among
themselves.
It might, however, be reasonable for the fraction-of-shared-buffers
limitation to have something to do with autovacuum_max_workers, so that
you can't squeeze yourself out of shared_buffers if you set that number
really high. IOW, I think the upthread suggestion of
min(shared_buffers/8/autovacuum_workers, 16MB) is basically the right
idea, though we could debate the exact constants.
regards, tom lane
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