| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Tomas Vondra <tv(at)fuzzy(dot)cz>, Jim Nasby <jim(at)nasby(dot)net>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: estimating # of distinct values |
| Date: | 2011-01-19 19:46:43 |
| Message-ID: | 25249.1295466403@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> ... I guess I'm just saying I'd think really, really hard
> before abandoning the idea of periodic sampling. You have to get an
> awful lot of benefit out of those cross-column stats to make it worth
> paying a run-time cost for them.
I've been trying to not discourage Tomas from blue-sky speculation,
but I have to say I agree with Robert that the chance of any usable
result from this approach is very very small. Feel free to do some
experimentation to prove us wrong --- but don't put a lot of effort
into it before that.
regards, tom lane
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