Re: XLogFlush invoked about twice as many times after 9.2 group commit enhancement

From: Peter Geoghegan <pg(at)heroku(dot)com>
To: Amit Langote <amitlangote09(at)gmail(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Peter Geoghegan <peter(dot)geoghegan86(at)gmail(dot)com>
Subject: Re: XLogFlush invoked about twice as many times after 9.2 group commit enhancement
Date: 2013-05-08 03:38:44
Message-ID: CAM3SWZTT0xK9G71MdXjX0YQOeC=FUbf-Et6XMoPWhBvcdGn_uA@mail.gmail.com
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On Tue, May 7, 2013 at 7:52 PM, Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> So, any rise in number of XLogFlush() calls should roughly
> be accounted for by increased throughput. Am I right in interpreting
> it this way?

I think so. There certainly isn't any question that the increased
throughput and the increased number of XLogFlush() calls are because
of the new group commit behavior. The cost of a WAL write + flush is
more effectively amortized, and so XLogFlush() calls becomes cheaper.
I'm not prepared to make any predictions as to exactly how they might
relate.

--
Peter Geoghegan

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