| From: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
|---|---|
| To: | "Greg Smith" <greg(at)2ndquadrant(dot)com>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com> |
| Cc: | "Josh Berkus" <josh(at)agliodbs(dot)com>, "Nathan Boley" <npboley(at)gmail(dot)com>, <pgsql-hackers(at)postgresql(dot)org>,"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Subject: | Re: Thoughts on statistics for continuously advancing columns |
| Date: | 2009-12-30 16:59:40 |
| Message-ID: | 4B3B329C020000250002DAB4@gw.wicourts.gov |
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| Lists: | pgsql-hackers |
Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> 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.
Well, the exception to that is if the stats say that your highest
value is x, and there are actually 500 million rows with values
greater than x, you can get some very bad plans for queries
requiring a range of values above x.
-Kevin
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