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

Re: two queries and dual cpu (perplexed)

From: John A Meinel <john(at)arbash-meinel(dot)com>
To: "Shoaib Burq (VPAC)" <sab(at)vpac(dot)org>,pgsql-performance(at)postgresql(dot)org
Subject: Re: two queries and dual cpu (perplexed)
Date: 2005-04-26 15:05:26
Message-ID: 426E58B6.2010607@arbash-meinel.com (view raw or flat)
Thread:
Lists: pgsql-performance
Shoaib Burq (VPAC) wrote:
> OK ... so just to clearify...  (and pardon my ignorance):
>
> I need to increase the value of 'default_statistics_target' variable and
> then run VACUUM ANALYZE, right? If so what should I choose for the
> 'default_statistics_target'?
>
> BTW I only don't do any sub-selection on the View.
>
> I have attached the view in question and the output of:
> SELECT oid , relname, relpages, reltuples
>         FROM pg_class ORDER BY relpages DESC;
>
> reg
> shoaib

Actually, you only need to alter the statistics for that particular
column, not for all columns in the db.

What you want to do is:

ALTER TABLE "ClimateChangeModel40"
	ALTER COLUMN <whatever the column is>
	SET STATISTICS 100;
VACUUM ANALYZE "ClimateChangeModel40";

The column is just the column that you have the "IX_ClimateId" index on,
I don't know which one that is.

The statistics value ranges from 1 - 1000, the default being 10, and for
indexed columns you are likely to want somewhere between 100-200.

If you set it to 100 and the planner is still mis-estimating the number
of rows, try 200, etc.

The reason to keep the number low is because with a high number the
planner has to spend more time planning. But especially for queries like
this one, you'd rather the query planner spent a little bit more time
planning, and got the right plan.

John
=:->

In response to

pgsql-performance by date

Next:From: Andreas PflugDate: 2005-04-26 15:53:46
Subject: Re: Table Partitioning: Will it be supported in Future?
Previous:From: Dave HeldDate: 2005-04-26 14:58:00
Subject: Re: two queries and dual cpu (perplexed)

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