Skip site navigation (1) Skip section navigation (2)

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
Message-ID: b1b9fac60903221756ifd951a3o4d8cb25854f2ade9@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
> I hit an interestinhg paper on n_distinct calculation:
>
> http://www.pittsburgh.intel-research.net/people/gibbons/papers/distinct-values-chapter.pdf
>
> 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 :]

Greetings
Marcin

In response to

pgsql-performance by date

Next:From: Tom LaneDate: 2009-03-23 02:18:57
Subject: Re: LIMIT confuses the planner
Previous:From: marcin mankDate: 2009-03-23 00:12:14
Subject: Re: LIMIT confuses the planner

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group