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Re: Optimizer : query rewrite and execution plan ?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: theo(at)flame(dot)co(dot)za, pgsql-performance(at)postgresql(dot)org
Subject: Re: Optimizer : query rewrite and execution plan ?
Date: 2008-02-11 16:44:42
Message-ID: 2685.1202748282@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> Say if cost of best plan >= N then recheck query for strangeness. If
> anything found, re-plan query.

Whatever makes you think that would be useful?

The usual result of undetected duplicate WHERE clauses is an
*underestimate* of runtime, not an overestimate (because it thinks
too few tuples will be selected).

			regards, tom lane

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