Answer / ramesh s

In software engineering, a connection pool is a cache of
database connections maintained by the database so that the
connections can be reused when the database receives future
requests for data. Connection pools are used to enhance the
performance of executing commands on a database. Opening and
maintaining a database connection for each user, especially
requests made to a dynamic database-driven website
application, is costly and wastes resources. In connection
pooling, after a connection is created, it is placed in the
pool and it is used over again so that a new connection does
not have to be established. If all the connections are being
used, a new connection is made and is added to the pool.
Connection pooling also cuts down on the amount of time a
user must wait to establish a connection to the database.

Answer / b.raja

Connections made via a DataSource object that is
implemented to work with a middle tier connection pool
manager will participate in connection pooling. This can
improve the performance dramatically because creating a new
connection is very expensive.
Connection Pool provides following features:
• Substantial improvement in the performance of DB
application can be accomplished by pre-caching the DB
connection objects
• CPM supplied DB connections are remote enable
• CPM supplied DB connections are cluster aware
• CPM supplied DB connections supports DTM
(distributed TXs)
• CPM supplied DB connections are not actual DB
Connection objects, in turn they are remote object, hence
even though client closes DB connection using con.close()
the actual connection may not be closed instead RMI
connection between client to CPM are closed
• CPM supplied DB connection objects are
serializable, hence client from any where in the network
can access DB connections
The classes and interfaces used for connection pooling are:
1. ConnectionPoolDataSource
2. PooledConnection
3. ConnectionEvent
4. ConnectionEventListener
Connection Pool Manager resided on middle tier
system uses these classes and interfaces behind the scenes.
When the ConnectionPooledDataSource object is called on to
create PooledConnection object, the connection pool manager
will register as a ConnectionEventListener object with the
new PooledConnection object. When the connection is closed
or there is an error, the connection pool manager (being
listener) gets a notification that includes a
ConnectionEvent object.

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