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Re: Index scan startup time

From: "Steinar H(dot) Gunderson" <sgunderson(at)bigfoot(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Index scan startup time
Date: 2006-03-30 13:00:41
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Thu, Mar 30, 2006 at 02:59:02PM +0200, Peter Eisentraut 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.
> The startup cost is the cost until the plan is set up to start outputting 
> rows.  It is not the time until the first row is found.

Well, point, my terminology was wrong. Still, what you're seeing is endless
scanning for the first row. I don't know your distribution, but are you
really sure state wouldn't have better selectivity?

/* Steinar */

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