From: Tom Lane <tgl@sss.pgh.pa.us>
To: Gaetano Mendola <mendola@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Useless sort by
Date: Mon, 13 Sep 2010 10:44:48 -0400
Message-ID: <12103.1284389088@sss.pgh.pa.us> (raw)
In-Reply-To: <i6ks04$2jet$1@news.hub.org>
References: <i6ks04$2jet$1@news.hub.org>
Gaetano Mendola <mendola@gmail.com> writes:
> because of that sort in the view definition the first query above
> takes not less than 3 seconds. I have solved this performance issue
> removing the sort from the view definition and putting it in the
> select reducing the time from > 3secons to < 150ms.
> Can not the optimizer take rid of that useless sort on those
> kind of queries ?
It is not the optimizer's job to second-guess the user on whether a sort
is really needed there. If we did make it throw away non-top-level
sorts, we'd have hundreds of users screaming loudly.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, mendola@gmail.com
Subject: Re: Useless sort by
In-Reply-To: <12103.1284389088@sss.pgh.pa.us>
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