According to the Tom Kytes :
• Each pool is confined to a single middle-tier node.
• A proliferation of pools results in excessive number of pre-allocated database servers and excessive database server memory consumption.
• Workload is distributed unequally across pools.
Oracle Database 11g comes preinstalled with a default connection pool but it is shut down. To start it, use:
SQL> execute dbms_connection_pool.start_pool;
Now to connect to the pooled connections instead of a regular session, all we have to do is add a line (SERVER=POOLED) to the TNS entry as shown below :
(ADDRESS = (PROTOCOL = TCP)(HOST = xxxx)(PORT = 1521))
(SERVER = POOLED)
(SID = PRONE3)
$c = oci_pconnect(‘myuser’, ‘mypassword’,’xxxx/PRONE3:POOLED’);
$c = oci_pconnect(‘myuser’, ‘mypassword’,’PRONE3_POOLED’);
In the above description we started the default pool that comes with Oracle with the default options. we can use the procedure CONFIGURE_POOL in the supplied package DBMS_CONNECTION_POOL :
For More detail visit below links :