Please look at http://pgfouine.info/tutorial.php also
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Installation instructions & Tutorial
Installation

You can either untar the pgFouine tarball or install the RPM package.

    * If you use the tarball, pgFouine is installed locally and can be 
run with ./pgfouine.php in the directory where you installed it.
    * If you install the RPM package, pgFouine is installed globally 
and you can run pgFouine with pgfouine.php.

How to enable query logging
PostgreSQL 7.x

Edit your postgresql.conf file (usually located in 
/var/lib/pgsql/data/) and set the following configuration directives:

    * To log queries slower than n milliseconds:

      syslog = 2
      log_min_duration_statement = n
      log_duration = false
      log_statement = false

      To log every query executed, set log_min_duration_statement to 0. 
Set it to -1 to disable query logging.
    * To log queries slower than n milliseconds AND duration for ALL 
queries (it only works with PostgreSQL 7.x; pgFouine counts every 
duration only once):

      syslog = 2
      log_min_duration_statement = n
      log_duration = true
      log_statement = false

Then edit your /etc/syslog.conf to set up a PostgreSQL facility:

local0.*		-/var/log/pgsql

You should also ignore PostgreSQL facility for the default log file otherwise you will log the queries twice:

*.info;mail.none;authpriv.none;cron.none;local0.none                /var/log/messages

Restart syslogd and PostgreSQL.

Apart from the extra I/O, the overhead of logging is barely noticeable. 
You can set syslog to send the log to another server through the 
network with @ip.ad.dr.ess.


PostgreSQL 8.x
Syslog configuration

Edit your postgresql.conf file (usually located in 
/var/lib/pgsql/data/) and set the following configuration directives:

    * To enable syslog logging:

      log_destination = 'syslog'
      redirect_stderr = off
      silent_mode = on

    * To log queries slower than n milliseconds:

      log_min_duration_statement = n
      log_duration = off
      log_statement = 'none'

      To log every query executed, set log_min_duration_statement to 0. Set it to -1 to disable query logging.

Then edit your /etc/syslog.conf to set up a PostgreSQL facility:

local0.*		-/var/log/pgsql

You should also ignore PostgreSQL facility for the default log file 
otherwise you will log the queries twice:

*.info;mail.none;authpriv.none;cron.none;local0.none                /var/log/messages

Restart syslogd and PostgreSQL.

Apart from the extra I/O, the overhead of logging is barely noticeable. 
You can set syslog to send the log to another server through the 
network with @ip.ad.dr.ess.


Filter on database and/or user

You can filter your log file on database and user using the -database 
and -user options. To do so, you need to configure the following 
log_line_prefix:

log_line_prefix = 'user=%u,db=%d'

Using stderr log file

Using the following configuration, you can log to stderr instead of 
syslog. This is not recommended as we cannot guarantee the consistency 
of statements if they are multilines.

log_destination = 'stderr'
redirect_stderr = on
log_line_prefix = '%t [%p]: [%l-1] '

Usage

pgFouine is an easy to use command line tool. The following command 
generates an HTML report with all default options:

$ pgfouine.php -file your/log/file.log > your-report.html

The following command line displays a text report with only 10 queries 
in each list to the standard output:

$ pgfouine.php -file your/log/file.log -top 10 -format text

By using pgfouine.php -help, you can display the usage information.