From: Justin Pryzby <pryzby@telsasoft.com>
To: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Julien Rouhaud <rjuju123@gmail.com>
Cc: Tharakan, Robins <tharar@amazon.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: track_planning causing performance regression
Date: Mon, 19 Apr 2021 09:55:45 -0500
Message-ID: <20210419145545.GF7256@telsasoft.com> (raw)
In-Reply-To: <d4cb31e2-d43f-0811-8f10-cf8e2f052e5e@oss.nttdata.com>
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<CAH2-WznCT6rZYGYE_Zxf1oYDZVMyXqm+SWRx+R2b5-DX11pmpQ@mail.gmail.com>
<42a13b4c-e60c-c6e7-3475-8eff8050bed4@oss.nttdata.com>
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<bc8125cb-264e-5a48-7d1f-17b84df831ed@oss.nttdata.com>
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<646e5cae-5e8b-feaa-43dc-014bf355bf08@oss.nttdata.com>
<20210418233615.GB7256@telsasoft.com>
<d4cb31e2-d43f-0811-8f10-cf8e2f052e5e@oss.nttdata.com>
On Mon, Apr 19, 2021 at 11:44:05PM +0900, Fujii Masao wrote:
> On 2021/04/19 8:36, Justin Pryzby wrote:
> > Reviewing this change which was committed last year as
> > 321fa6a4a26c9b649a0fbec9fc8b019f19e62289
> >
> > On Fri, Jul 03, 2020 at 03:57:38PM +0900, Fujii Masao wrote:
> > > On 2020/07/03 13:05, Pavel Stehule wrote:
> > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com> napsal:
> > > >
> > > > Maybe there can be documented so enabling this option can have a negative impact on performance.
> > >
> > > Yes. What about adding either of the followings into the doc?
> > >
> > > Enabling this parameter may incur a noticeable performance penalty.
> > >
> > > or
> > >
> > > Enabling this parameter may incur a noticeable performance penalty,
> > > especially when a fewer kinds of queries are executed on many
> > > concurrent connections.
> >
> > Something seems is wrong with this sentence, and I'm not sure what it's trying
> > to say. Is this right ?
>
> pg_stat_statements users different spinlock for each kind of query.
> So fewer kinds of queries many sessions execute, fewer spinlocks
> they try to acquire. This may lead to spinlock contention and
> significant performance degration. This is what the statement is
> trying to say.
What does "kind" mean ? I think it means a "normalized" query or a "query
structure".
"a fewer kinds" is wrong, so I think the docs should say "a small number of
queries" or maybe:
> > > Enabling this parameter may incur a noticeable performance penalty,
> > > especially similar queries are run by many concurrent connections and
> > > compete to update the same pg_stat_statements entry
--
Justin
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Cc: pryzby@telsasoft.com, masao.fujii@oss.nttdata.com, pavel.stehule@gmail.com, pg@bowt.ie, rjuju123@gmail.com, tharar@amazon.com
Subject: Re: track_planning causing performance regression
In-Reply-To: <20210419145545.GF7256@telsasoft.com>
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