From: Bruce Momjian <bruce@momjian.us>
To: Andrew Dunstan <andrew@dunslane.net>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: Josh Berkus <josh@agliodbs.com>
Cc: Amit Kapila <amit.kapila@huawei.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Performance bug in prepared statement binding in 9.2?
Date: Mon, 9 Sep 2013 21:04:20 -0400
Message-ID: <20130910010420.GA32160@momjian.us> (raw)
In-Reply-To: <522E69F1.8070203@dunslane.net>
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On Mon, Sep 9, 2013 at 08:38:09PM -0400, Andrew Dunstan wrote:
>
> On 08/01/2013 03:20 PM, Jeff Janes wrote:
> >On Thu, Aug 1, 2013 at 10:58 AM, Josh Berkus <josh@agliodbs.com> wrote:
> >>Amit, All:
> >>
> >>So we just retested this on 9.3b2. The performance is the same as 9.1
> >>and 9.2; that is, progressively worse as the test cycles go on, and
> >>unacceptably slow compared to 8.4.
> >>
> >>Some issue introduced in 9.1 is causing BINDs to get progressively
> >>slower as the PARSEs BINDs get run repeatedly. Per earlier on this
> >>thread, that can bloat to 200X time required for a BIND, and it's
> >>definitely PostgreSQL-side.
> >>
> >>I'm trying to produce a test case which doesn't involve the user's
> >>application. However, hints on other things to analyze would be keen.
> >Does it seem to be all CPU time (it is hard to imagine what else it
> >would be, but...)
> >
> >Could you use oprofile or perf or gprof to get a profile of the
> >backend during a run? That should quickly narrow it down to which C
> >function has the problem.
> >
> >Did you test 9.0 as well?
>
>
> This has been tested back to 9.0. What we have found is that the
> problem disappears if the database has come in via dump/restore, but
> is present if it is the result of pg_upgrade. There are some
> long-running transactions also running alongside this - we are
> currently planning a test where those are not present. We're also
> looking at constructing a self-contained test case.
>
> Here is some perf output from the bad case:
>
> + 14.67% postgres [.] heap_hot_search_buffer
OK, certainly looks like a HOT chain issue. I think there are two
possibilities:
1) the heap or index file is different from a dump/restore vs.
pg_upgrade
2) some other files is missing or changed between the two
My guess is that the dump/restore removes all the HOT chains as it just
dumps the most recent value of the chain. Could it be HOT chain
overhead that you are seeing, rather than a pg_upgrade issue/bug?
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
--
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To: pgsql-performance@postgresql.org
Cc: bruce@momjian.us, andrew@dunslane.net, jeff.janes@gmail.com, josh@agliodbs.com, amit.kapila@huawei.com
Subject: Re: Performance bug in prepared statement binding in 9.2?
In-Reply-To: <20130910010420.GA32160@momjian.us>
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