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From: scott ribe <scott_ribe@elevated-dev.com>
To: Greg Stark <stark@mit.edu>
Cc: pgsql-admin@lists.postgresql.org
Subject: Re: Estimate maintenance_work_mem for CREATE INDEX
Date: Tue, 19 Dec 2017 07:29:29 -0700
Message-ID: <76272163-2E25-4997-9D6F-983F0BBA5885@elevated-dev.com> (raw)
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	<CAM-w4HOOhfif6nao1GU9B-8rzb1vy5YGocW+XFy4HOQmupvZbw@mail.gmail.com>

> On Dec 19, 2017, at 7:14 AM, Greg Stark <stark@mit.edu> wrote:
> 
> I'm not clear how you would determine how much memory is needed to
> sort a table without actually doing the sort though. So that would be
> more of an EXPLAIN ANALYZE wouldn't it?

I'd think EXPLAIN could use a quite rough approximation, say based on a rather sparse random sampling of values. EXPLAIN ANALYZE might involve a whole table scan, or might involve more dense sampling.

--
Scott Ribe
https://www.linkedin.com/in/scottribe/
(303) 722-0567





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