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Re: tuplesort memory usage: grow_memtuples

From: Peter Geoghegan <peter(at)2ndquadrant(dot)com>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: tuplesort memory usage: grow_memtuples
Date: 2012-07-25 21:51:50
Message-ID: CAEYLb_VuaHP3hNMJkB6fERPwQSsfyeKQ3YO35id0kc3n1N==dg@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 3 March 2012 20:22, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> Add it all up, and instead of pre-reading 32 consecutive 8K blocks, it
> pre-reads only about 1 or 2 consecutive ones on the final merge.  Now
> some of those could be salvaged by the kernel keeping track of
> multiple interleaved read ahead opportunities, but in my hands vmstat
> shows a lot of IO wait and shows reads that seem to be closer to
> random IO than large read-ahead.  If it used truly efficient read
> ahead, CPU would probably be limiting.

Can you suggest a benchmark that will usefully exercise this patch?

-- 
Peter Geoghegan       http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training and Services

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