| From: | mlw <markw(at)mohawksoft(dot)com> |
|---|---|
| To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Thomas Lockhart <thomas(at)fourpalms(dot)org>, Lincoln Yeoh <lyeoh(at)pop(dot)jaring(dot)my>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Louis-David Mitterrand <vindex(at)apartia(dot)org>, PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Index Scans become Seq Scans after VACUUM ANALYSE |
| Date: | 2002-04-17 18:50:38 |
| Message-ID: | 3CBDC3FE.9DEFE4F7@mohawksoft.com |
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| Lists: | pgsql-hackers |
Peter Eisentraut wrote:
>
> mlw writes:
>
> > Adding huristics, such as weighting for index scans, is not making the planner
> > stupider. It is making it smarter and more flexable.
>
> If life was as simple as index or no index then this might make some
> sense. But in general the planner has a whole bunch of choices of join
> plans, sorts, scans, and the cost of an individual index scan is hidden
> down somewhere in the leaf nodes, so you can't simply say that plans of
> type X should be preferred when the cost estimates are close.
>
No doubt, no one is arguing that it is easy, but as I said in a branch of this
discussion, when the planner has multiple choices, and the cost ranges
overlapp, the relative numbers are not so meaningful that huristics would not
improve the algorithm.
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