From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Willy-Bas Loos <willybas(at)gmail(dot)com> |
Cc: | Josh Berkus <josh(at)agliodbs(dot)com>, npboley(at)gmail(dot)com, pgsql-performance(at)postgresql(dot)org, pgsql-general(at)postgresql(dot)org |
Subject: | Re: [PERFORM] change sample size for statistics |
Date: | 2011-06-29 02:55:45 |
Message-ID: | BANLkTinre-NTvXTsMqnw6+LrKJO0ex0_OA@mail.gmail.com |
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Lists: | pgsql-general pgsql-performance |
On Mon, Jun 13, 2011 at 6:33 PM, Willy-Bas Loos <willybas(at)gmail(dot)com> wrote:
> On Fri, Jun 10, 2011 at 9:58 PM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
>>
>> It's not 10%. We use a fixed sample size, which is configurable on the
>> system, table, or column basis.
>
> It seems that you are referring to "alter column set statistics" and
> "default_statistics_target", which are the number of percentiles in the
> histogram (and MCV's) .
> I mean the number of records that are scanned by analyze to come to the
> statistics for the planner, especially n_disctict.
In 9.0+ you can do ALTER TABLE .. ALTER COLUMN .. SET (n_distinct = ...);
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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