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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Kyle Bateman <kyle@actarg.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: PG 8.2beta reordering working for this case?
Date: Mon, 09 Oct 2006 10:15:23 -0400
Message-ID: <1600.1160403323@sss.pgh.pa.us> (raw)
In-Reply-To: <4529DDCC.6010909@actarg.com>
References: <44DF6582.4000806@actarg.com>
	<82mza77rch.fsf@mid.bfk.de>
	<44E11E1A.8020507@actarg.com>
	<27367.1155606817@sss.pgh.pa.us>
	<44E349BA.4070205@actarg.com>
	<26676.1155747492@sss.pgh.pa.us>
	<44E3840E.4080502@actarg.com>
	<45284DBC.3060901@actarg.com>
	<25779.1160329771@sss.pgh.pa.us>
	<4529DDCC.6010909@actarg.com>

Kyle Bateman <kyle@actarg.com> writes:
> BTW, explain analyze still says 10 seconds of run time (and takes 10 
> seconds to run), but when I remove the explain analyze, the query runs 
> in about a second.  What's that all about?

Instrumentation overhead ... you're probably running this on a PC with a
very slow clock-reading capability.  Each node output row counted by
explain analyze takes two gettimeofday() calls, and apparently it's not
unusual for those to take several microseconds on cheap motherboards,
even when the CPU is nominally very fast.

			regards, tom lane



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