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Re: LIMIT confuses the planner

From: marcin mank <marcin(dot)mank(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: kouber(at)saparev(dot)com, pgsql-performance(at)postgresql(dot)org
Subject: Re: LIMIT confuses the planner
Date: 2009-03-23 00:56:50
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Lists: pgsql-performance
> I hit an interestinhg paper on n_distinct calculation:
> the PCSA algorithm described there requires O(1) calculation per
> value. Page 22 describes what to do with updates streams.
> This I think (disclaimer: I know little about PG internals) means that
> the n_distinct estimation can be done during vacuum time (it would
> play well with the visibility map addon).
> What do You think?

ok, if You think that calculating a has function of every data field
for each insert or delete is prohibitive, just say so and don`t bother
reading the paper :]


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