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Re: Planner mis-estimation using nested loops followup

From: "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>
To: "Chris Kratz" <chris(dot)kratz(at)vistashare(dot)com>
Cc: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Planner mis-estimation using nested loops followup
Date: 2008-03-18 19:46:51
Message-ID: dcc563d10803181246sbdc7425u838ff2baf70faeb6@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Tue, Mar 18, 2008 at 9:58 AM, Chris Kratz <chris(dot)kratz(at)vistashare(dot)com> wrote:
> Y, turning nested loops off in specific cases has increased performance
> greatly.  It didn't fix the planner mis-estimation, just the plan it chose.
> It's certainly not a panacea, but it's something we now try early on when
> trying to speed up a query that matches these characteristics.

I have to admit I've had one or two reporting queries in the past that
turning off nested_loop was the only reasonable fix due to
misestimation.  I'd tried changing the stats targets etc and nothing
really worked reliably to prevent the nested_loop from showing up in
the wrong places.

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