Re: Expected accuracy of planner statistics - Mailing list pgsql-general

From John D. Burger
Subject Re: Expected accuracy of planner statistics
Date
Msg-id A1E93AA5-9312-4C95-A509-4434FDDD06BD@mitre.org
Whole thread Raw
In response to Re: Expected accuracy of planner statistics  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: Expected accuracy of planner statistics  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-general
Tom Lane wrote:

> The information we've seen says that the only statistically
> reliable way
> to arrive at an accurate n_distinct estimate is to examine most of the
> table :-(.

> IIRC I picked an equation out of the literature partially on the basis
> of it being simple and fairly cheap to compute...

I'm very curious about this - can you recall where you got this, or
at least point me to where in the code this happens?

Thanks.

- John Burger
   MITRE

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