| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Jim C(dot) Nasby" <jim(at)nasby(dot)net> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Cross-table statistics idea |
| Date: | 2006-09-27 02:42:46 |
| Message-ID: | 2906.1159324966@sss.pgh.pa.us |
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"Jim C. Nasby" <jim(at)nasby(dot)net> writes:
> ISTM that we could gain additional insight on how many rows would likely
> result from a join be comparing the "shape" of the histogram for the
> joining columns.
eqjoinsel already does this for the case of comparing the MCV lists.
If you're serious about using the histograms: well, maybe, but it seems
to require far stronger assumptions about the behavior of the datatype
than we use now.
> Am I right about how our estimates work right now? Where can I look in
> the code? Has anyone looked down this path in the past?
src/backend/utils/adt/selfuncs.c
regards, tom lane
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