pgpool-II allows multiple PostgreSQL servers (DB nodes) to be
connected, which enables queries to be executed simultaneously on all
servers.

It enables "parallel query" processing. Also, pgpool-II can be started
as pgpool-I by changing configuration parameters. pgpool-II that is
executed in pgpool-I mode enables multiple DB nodes to be connected,
which was not possible in pgpool-I.

WWW:	http://pgpool.projects.postgresql.org/pgpool-II/en/