Re: Planner really hates nested loops

From: "Magnus Hagander" <mha(at)sollentuna(dot)net>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "David Brown" <time(at)bigpond(dot)net(dot)au>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Planner really hates nested loops
Date: 2005-02-03 16:41:37
Message-ID: 6BCB9D8A16AC4241919521715F4D8BCE4767B0@algol.sollentuna.se
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> > I'm hoping someone can shed some light on these results.
>
> Not without a lot more detail on how you *got* the results.
> What exactly did you do to force the various plan choices?
> (I see some ridiculous choices of indexscans, for instance,
> suggesting improper use of enable_seqscan in some cases.)
> And what's the "cache rows" and "disk rows" stuff, and how do
> you know that what you were measuring is actually what you
> think it is? I have zero confidence in Windows-atop-ATA as a
> platform for measuring disk-related behaviors, because I
> don't think you can control or even know what caching is going on.

You can control the writeback-cache from Device Manager->(the
disk)->Policies. And if that is turned off, fsync definitly should write
through, just as on *nix. (write-cache is on by default, no surprise)

AFAIK, you can't control what is cached for reading.

//Magnus

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