| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Peter Bierman <bierman(at)apple(dot)com> |
| Cc: | Dann Corbit <DCorbit(at)connx(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Suggestion for optimization |
| Date: | 2002-04-05 23:41:32 |
| Message-ID: | 11039.1018050092@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Peter Bierman <bierman(at)apple(dot)com> writes:
> ... Your comment: "An
> accurate cardinality figure can greatly enhance the optimizer's
> ability to perform joins in the correct order" was intriguing, and I'd
> be interested in Tom's thoughts on just that bit.
Approximate figures are quite sufficient for the planner's purposes.
AFAICS, making them exact would not improve the planning estimates
at all, because there are too many other sources of error. We have
approximate stats already via vacuum/analyze statistics gathering.
regards, tom lane
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