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Re: Thoughts on statistics for continuously advancing columns

From: Greg Stark <stark(at)mit(dot)edu>
To: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>,Greg Stark <gsstark(at)mit(dot)edu>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>,Josh Berkus <josh(at)agliodbs(dot)com>,Nathan Boley <npboley(at)gmail(dot)com>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: Thoughts on statistics for continuously advancing columns
Date: 2009-12-30 22:31:09
Message-ID: 3b1161ac-c5bc-42cb-9923-bdd610453d07@email.android.com (view raw or flat)
Thread:
Lists: pgsql-hackers
well that's interesting because they claim to be doing exactly the same amount of I/O in terms of pages.

In the first case it's reading 3/4 of the table so it's effectively doing a sequential scan. In the second case it's only scanning 7.5% so you would expect it to be slower but not that much slower.

If as you say the rows are very wide then the other part of the equation will be TOAST table I/O though. I'm not sure what it would look like but I bet analyze isn't optimized to handle well -- not much of postgres really knows about TOAST. It'll be accessing the same number of TOAST records but out of a much bigger TOAST table. 
--
greg

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