Re: Performance Implications of Using Exceptions

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robins Tharakan <tharakan@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Performance Implications of Using Exceptions
Date: Tue, 01 Apr 2008 00:29:35 -0400
Message-ID: <20193.1207024175@sss.pgh.pa.us> (raw)
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"Robins Tharakan" <tharakan@gmail.com> writes:
> Would it fine to consider that an UPDATE query that found no records to
> update is (performance wise) the same as a SELECT query with the same WHERE
> clause ?

> As in, does an UPDATE query perform additional overhead even before it finds
> the record to work on ?

The UPDATE would fire BEFORE STATEMENT and AFTER STATEMENT triggers, if
there are any.  Also, it would take a slightly stronger lock on the
table, which might result in blocking either the UPDATE itself or some
concurrent query where a plain SELECT would not've.

There might be some other corner cases I've forgotten.  But in the basic
case I think your assumption is correct.

			regards, tom lane

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