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Re: Index scan startup time

From: Michael Stone <mstone+postgres(at)mathom(dot)us>
To: pgsql-performance(at)postgresql(dot)org
Cc: Peter Eisentraut <peter_e(at)gmx(dot)net>
Subject: Re: Index scan startup time
Date: 2006-03-30 12:42:53
Message-ID: 20060330124251.GK6811@mathom.us (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, Mar 30, 2006 at 02:31:34PM +0200, Steinar H. Gunderson wrote:
>Well, it's logical enough; it scans along activity_id until it finds one with
>state=10000 or state=10001. You obviously have a _lot_ of records with low
>activity_id and state none of these two, so Postgres needs to scan all those
>records before it founds 100 it can output. This is the “startup cost” you're
>seeing.

Yes. And the estimates are bad enough (orders of magnitude) that I can't 
help but wonder whether pg could come up with a better plan with better 
statistics:

>>>>   ->  Index Scan using activity_pk on activity  (cost=0.00..40717259.91 rows=6538650 width=8) (actual time=207356.050..207356.722 rows=100 loops=1) Filter: ((state = 10000) OR (state = 10001))

Mike Stone

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Subject: Re: Index scan startup time
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