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Re: in-memory sorting

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Samuel Gendler <sgendler(at)ideasculptor(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: in-memory sorting
Date: 2010-08-19 13:29:39
Message-ID: 26184.1282224579@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Samuel Gendler <sgendler(at)ideasculptor(dot)com> writes:
> Answered my own question.  Cranking work_mem up to 350MB revealed that
> the in-memory sort requires more memory than the disk sort.

Yeah.  The on-disk representation of sortable data is tighter than the
in-memory representation for various reasons, mostly that we're willing
to work at making it small.  Datums aren't necessarily properly aligned
for example, and there's also palloc overhead to consider in-memory.

			regards, tom lane

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