Re: pg_stat_wal_write statistics view

From: Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com>
To: Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
Cc: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_stat_wal_write statistics view
Date: 2017-09-11 16:04:53
Message-ID: CAGz5QCLH-NGV62CkZBW42VEEYCGRu1hoC8VnYYd84Niux+e7xQ@mail.gmail.com
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On Wed, Sep 6, 2017 at 9:16 AM, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com> wrote:
>
> Attached the latest patch and performance report.
>
While looking into the patch, I realized that a normal backend has to
check almost 10 if conditions at worst case inside XLogWrite(6 in
am_background_process method, 1 for write, 1 for blocks, 2 for
fsyncs), just to decide whether it is a normal backend or not. The
count is more for walwriter process. Although I've not done any
performance tests, IMHO, it might add further overhead on the
XLogWrite Lock.

I was thinking whether it is possible to collect all the stats in
XLogWrite() irrespective of the type of backend and update the shared
counters at once at the end of the function. Thoughts?

--
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com

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