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Re: [PATCH] Improve EXPLAIN ANALYZE overhead by sampling

From: "Rocco Altier" <RoccoA(at)Routescape(dot)com>
To: "Martijn van Oosterhout" <kleptog(at)svana(dot)org>,<pgsql-patches(at)postgresql(dot)org>
Cc: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
Subject: Re: [PATCH] Improve EXPLAIN ANALYZE overhead by sampling
Date: 2006-05-09 21:16:57
Message-ID: 6E0907A94904D94B99D7F387E08C4F57010A5E8C@FALCON.INSIGHT (view raw or flat)
Thread:
Lists: pgsql-patches
> - To get this close it needs to get an estimate of the sampling
overhead.
> It does this by a little calibration loop that is run once per
backend.
> If you don't do this, you end up assuming all tuples take the same
time
> as tuples with the overhead, resulting in nodes apparently taking
> longer than their parent nodes. Incidently, I measured the overhead to
> be about 3.6us per tuple per node on my (admittedly slightly old)
> machine.

Could this be deferred until the first explain analyze?  So that we
aren't paying the overhead of the calibration in all backends, even the
ones that won't be explaining?

	-rocco

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