Postgres Pro
Downloads
Home   >   mailing lists

Re: How to specify/mock the statistic data of tables in PostgreSQL - Mailing list pgsql-general

From Atri Sharma
Subject Re: How to specify/mock the statistic data of tables in PostgreSQL
Date
Msg-id 66B7D041-6C4B-407E-B0AA-66AB26716144@gmail.com
Whole thread Raw
In response to Re: How to specify/mock the statistic data of tables in PostgreSQL  ("ygnhzeus" <ygnhzeus@gmail.com>)
Responses Re: How to specify/mock the statistic data of tables in PostgreSQL  (Amit Langote <amitlangote09@gmail.com>)
List pgsql-general
Tree view


Sent from my iPad

On 10-Jan-2014, at 19:42, "ygnhzeus" <ygnhzeus@gmail.com> wrote:

body{FONT-SIZE:12pt; FONT-FAMILY:宋体,serif;}
Thanks for your reply.
So correlation is not related to the calculation of selectivity right? If I force PostgreSQL not to optimize the join order (by setting join_collapse_limit and from_collapse_limit  to 1) , is there any other factor that may affect the structure of execution plan regardless of the data access method.
 
2014-01-10
ygnhzeus
发件人：Amit Langote <amitlangote09@gmail.com>
发送时间：2014-01-10 22:00
主题：Re: [GENERAL] How to specify/mock the statistic data of tables in PostgreSQL
收件人："ygnhzeus"<ygnhzeus@gmail.com>
抄送："pgsql-general"<pgsql-general@postgresql.org>
 


AFAIK, correlation is involved in calculation of the costs that are used for deciding the type of access.If the correlation is low, index scan can lead to quite some random reads, hence leading to higher costs.

Regards,

Atri

pgsql-general by date:

Previous
From: "ygnhzeus"
Date:
Subject: Re: How to specify/mock the statistic data of tables in PostgreSQL
Next
From: Amit Langote
Date:
Subject: Re: How to specify/mock the statistic data of tables in PostgreSQL