| From: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
|---|---|
| To: | <postgres(at)cybertec(dot)at>,"Robert Haas" <robertmhaas(at)gmail(dot)com> |
| Cc: | "Heikki Linnakangas" <heikki(dot)linnakangas(at)enterprisedb(dot)com>, <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: index-only scans |
| Date: | 2011-08-12 21:39:26 |
| Message-ID: | 4E45573E020000250003FE9B@gw.wicourts.gov |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> That's one of the points I asked for feedback on in my original
> email. "How should the costing be done?"
It seems pretty clear that there should be some cost adjustment. If
you can't get good numbers somehow on what fraction of the heap
accesses will be needed, I would suggest using a magic number based
on the assumption that half the heap access otherwise necessary will
be done. It wouldn't be the worst magic number in the planner. Of
course, real numbers are always better if you can get them.
-Kevin
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