| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: change sample size for statistics |
| Date: | 2011-06-10 19:58:19 |
| Message-ID: | 4DF2775B.7070501@agliodbs.com |
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| Thread: | |
| Lists: | pgsql-general pgsql-performance |
On 6/10/11 5:15 AM, Willy-Bas Loos wrote:
> Hi,
>
> is there a way to change the sample size for statistics (that analyze
> gathers)?
> It is said to be 10%. i would like to raise that, because we are getting bas
> estimations for n_distinct.
It's not 10%. We use a fixed sample size, which is configurable on the
system, table, or column basis.
Some reading (read all these pages to understand what you're doing):
http://www.postgresql.org/docs/9.0/static/planner-stats.html
http://www.postgresql.org/docs/9.0/static/runtime-config-query.html#RUNTIME-CONFIG-QUERY-OTHER
http://www.postgresql.org/docs/9.0/static/planner-stats-details.html
http://www.postgresql.org/docs/9.0/static/sql-altertable.html
(scroll down to "set storage" on that last page)
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com
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