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Re: Thoughts on statistics for continuously advancing columns

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
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 16:46:49
Message-ID: 4B3B83F9.6070308@2ndquadrant.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Joshua D. Drake wrote:
> We normally don't notice because most sets won't incur a penalty. We got a customer who
> has a single table that is over 1TB in size... We notice. Granted that is the extreme
> but it would only take a quarter of that size (which is common) to start seeing issues.
>   

Right, and the only thing that makes this case less painful is that you 
don't really need the stats to be updated quite as often in situations 
with that much data.  If, say, your stats say there's 2B rows in the 
table but there's actually 2.5B, that's a big error, but unlikely to 
change the types of plans you get.  Once there's millions of distinct 
values it's takes a big change for plans to shift, etc.

-- 
Greg Smith    2ndQuadrant   Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com  www.2ndQuadrant.com


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