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PostgreSQL Enterprise Server (PgES) provides connection pooling support through the PgBouncer Lightweight connection pooler that is included in the PgES distribution.
PgBouncer is a PostgreSQL connection pooler. Any target application can be connected to pgbouncer as if it were a PostgreSQL server, and pgbouncer will create a connection to the actual server, or it will reuse one of its existing connections. The aim of pgbouncer is to lower the performance impact of opening new connections to PostgreSQL. In order not to compromise transaction semantics for connection pooling, PgBouncer supports several types of pooling when rotating connections:
Session pooling: Most polite method. When a client connects, a server connection will be assigned to it for the whole duration the client stays connected. When the client disconnects, the server connection will be put back into the pool. This is the default method.
Transaction pooling: A server connection is assigned to a client only during a transaction. When PgBouncer notices that transaction is over, the server connection will be put back into the pool.
Statement pooling: Most aggressive method. The server connection will be put back into the pool immediately after a query completes. Multi-statement transactions are disallowed in this mode as they would break.
The administration interface of pgbouncer consists of some new SHOW commands available when connected to a special "virtual" database pgbouncer.