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Re: [PERFORMANCE] work_mem vs temp files issue

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Jaime Casanova <jcasanov(at)systemguards(dot)com(dot)ec>, decibel <decibel(at)decibel(dot)org>, psql performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: [PERFORMANCE] work_mem vs temp files issue
Date: 2010-01-13 15:42:38
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I had an idea at one point of making explain show the planned and
> actual # of batches for each hash join.  I believe that "actual # of
> batches > 1" is isomorphic to "hash join went to disk".  The code is
> actually pretty easy; the hard part is figuring out what to do about
> the UI.  The choices seem to be:

> 1. Create a new EXPLAIN option just for this - what would we call it?
> 2. Think of some more, similar things and come up with a new EXPLAIN
> option covering all of them - what else would go along with?
> 3. Sandwhich it into an existing EXPLAIN option, most likely VERBOSE.
> 4. Display it by default.

Treat it the same as the Sort-node actual usage information.  We did not
add a special option when we added that.

			regards, tom lane

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