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Re: docs update for count(*) and index-only scans

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Josh Kupershmidt <schmiddy(at)gmail(dot)com>
Cc: pgsql-docs <pgsql-docs(at)postgresql(dot)org>
Subject: Re: docs update for count(*) and index-only scans
Date: 2011-11-01 22:51:02
Message-ID: 26833.1320187862@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-docs
Josh Kupershmidt <schmiddy(at)gmail(dot)com> writes:
> func.sgml still claims that a sequential scan is the only way to
> execute a SELECT COUNT(*) query. I think this note should just be
> removed from the current docs, given the existence of index-only
> scans; patch attached.

Well, it might need adjustment, but I don't think we should remove it
outright.  The people who complain that COUNT(*) is not O(1) are still
going to be complaining.  On tables that are not read-mostly, there's
no reason to expect that index-only scans will even provide a material
speed boost, let alone be close to free.

			regards, tom lane

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