Connection pooling, Why we go for connection pooling in PostgreSQL, When your application demands for very good number of concurrent connection hits then you need to approach it, because Connection pool sits between your application and the database.

Idea behind connection pool is that you have enough connections to use of all the available resources and any incoming requests are re-used without dropping the database connection and keeping ready for a new connection to use.

pgbouncer is lightweight connection pooler. pgBouncer runs as a single process, not spawning a process per connection, which relies on library named libevent for connection pooling.

pgbouncer setup on PostgreSQL 9.0 is very simple, however there is small change with the latest version you need to create manual pg_auth file. pgbouncer uses pg_auth file for user authentication. Earlier verion of PostgreSQL 9.0, you can find the pg_auth file under $PGDATA/global/pg_auth, now in the latest version that file has been removed and placed in pg_catalog as table ‘pg_auth’.

pgbouncer Setup:

1. First, download libevent library for pgbouncer.
Download link for libevent:
http://www.monkey.org/~provos/libevent-2.0.12-stable.tar.gz

tar -xvf libevent-2.0.12-stable.tar.gz

cd libevent-2.0.12-stable

./configure 

make

make install

2. Download the latest pgbouncer tar and configure to your PostgreSQL 9.0.
http://pgfoundry.org/frs/download.php/2912/pgbouncer-1.4.tgz

tar -xvf pgbouncer-1.4

cd pgbouncer-1.4

./configure --prefix=/opt/PostgreSQL/9.0/bin

make

make install

3. Create a libevent-i386.conf file in /etc/ld.so.conf.d directory

vi /etc/ld.so.conf.d/libevent-i386.conf

/usr/local/lib

:wq!

4. Run the ldconfig to apply new changes.

#ldconfig

5. Change the ownership of pgbouncer utility in PostgreSQL binary to postgres user.

chown -R postgres:postgres /opt/PostgreSQL/9.0/bin/bin/pgbouncer

6. Create the pgbouncer_auth file for users authentication.

7. Create pgbouncer.ini file with postgres user permission under /etc directory.

8. Start pgbouncer

-bash-4.1$ ./pgbouncer -d /etc/pgbouncer.ini

2011-08-14 11:42:00.925 1949 LOG File descriptor limit: 1024 (H:1024), max_client_conn: 1000, max fds possible: 1010

9. Connect to the databases using pgbouncer

10. Getting help: Connect to pgbouncer database and get helped.

$ psql -p 6432 -U postgres pgbouncer

pgbouncer=# show help;

For better understanding on pg_auth you can find in below link by ‘depesz’.
http://www.depesz.com/index.php/2010/12/04/auto-refreshing-password-file-for-pgbouncer/

Do post your comments which are highly appreciated.

–Raghav