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Re: Column correlation drifts, index ignored again

From: "Ed L(dot)" <pgsql(at)bluepolka(dot)net>
To: Kevin Brown <kevin(at)sysexperts(dot)com>,Postgres Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Column correlation drifts, index ignored again
Date: 2004-02-24 20:54:15
Message-ID: 200402241354.15025.pgsql@bluepolka.net (view raw or flat)
Thread:
Lists: pgsql-performance
On Tuesday February 24 2004 1:14, Kevin Brown wrote:
>
> One problem I've been running into is the merge join spilling to disk
> because sort_mem isn't big enough.  The problem isn't that this is
> happening, it's that I think the planner is underestimating the impact
> that doing this will have on the time the merge join takes.  Does the
> planner even account for the possibility that a sort or join will spill
> to disk?  Spilling to disk like that will suddenly cause sequential
> reads to perform much more like random reads, unless the sequential
> scans are performed in their entirety between sorts/merges.

How do you know the merge join is spilling to disk?  How are you identifying 
that?  Just assuming from vmstat?  iostat?

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Subject: Re: Column correlation drifts, index ignored again
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