From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
---|---|
To: | "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, "Imai, Yoshikazu" <imai(dot)yoshikazu(at)jp(dot)fujitsu(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Simon Riggs <simon(at)2ndquadrant(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Speed up transaction completion faster after many relations are accessed in a transaction |
Date: | 2019-07-22 02:29:33 |
Message-ID: | CAKJS1f_c4GY3dB+FGh6UbF5XYQhc6N1Bxv6sY=efUdqNODqbGQ@mail.gmail.com |
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On Mon, 22 Jul 2019 at 14:21, Tsunakawa, Takayuki
<tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> wrote:
>
> From: David Rowley [mailto:david(dot)rowley(at)2ndquadrant(dot)com]
> > I personally don't think that's true. The only way you'll notice the
> > LockReleaseAll() overhead is to execute very fast queries with a
> > bloated lock table. It's pretty hard to notice that a single 0.1ms
> > query is slow. You'll need to execute thousands of them before you'll
> > be able to measure it, and once you've done that, the lock shrink code
> > will have run and the query will be performing optimally again.
>
> Maybe so. Will the difference be noticeable between plan_cache_mode=auto (default) and plan_cache_mode=custom?
For the use case we've been measuring with partitioned tables and the
generic plan generation causing a sudden spike in the number of
obtained locks, then having plan_cache_mode = force_custom_plan will
cause the lock table not to become bloated. I'm not sure there's
anything interesting to measure there. The only additional code that
gets executed is the hash_get_num_entries() and possibly
hash_get_max_bucket. Maybe it's worth swapping the order of those
calls since most of the time the entry will be 0 and the max bucket
count threshold won't be exceeded.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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