Message-ID: <4D49934A.6010104@2ndquadrant.com>
Date: Wed, 02 Feb 2011 12:24:26 -0500
From: Greg Smith <greg@2ndquadrant.com>
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To: Cesar Arrieta <cesar.cba@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: About pg_stat_activity
References: <AANLkTi=XvdtT0mDQC1CmU=GwzhhbCKuhVvxRMzTN2_Ki@mail.gmail.com>
In-Reply-To: <AANLkTi=XvdtT0mDQC1CmU=GwzhhbCKuhVvxRMzTN2_Ki@mail.gmail.com>
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Cesar Arrieta wrote:
> im developing an app that saves information included in 
> "pg_stat_activity" view in order to monitor querys. The objective of 
> this app is to gather information about querys that take to long to 
> finish and overload the server.

I hope you're already setting log_min_duration_statement, then analyzing 
the resulting logs using something like pgFouine.  If you have 
PostgreSQL 8.4 or later, possibly add loading the auto_explain module as 
well, or collecting the data using pg_stat_statements instead can be 
useful.  Trying to grab this info in real-time from pg_stat_activity 
instead is a lot of work and won't give you results as good.  If you're 
already doing something like that and are just looking to increase the 
amount of info you collect by also looking at pg_stat_activity, that can 
be worthwhile.

Maciek just gave the quickest answer to your main question; I'll just 
add that reading the source code to the file system_views.sql will show 
you how pg_stat_activity as well as other interesting built-in views work.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books