Oracle listener refuses connections or unavailable

If a large number of connections (more than the value of PROCESSES) to Oracle are opened and closed within a short period of time (~10 min), the listener service might assume that the Oracle instance is unable to accept new connections and block new connections until it receives an update on load and connection status from the Oracle instance.

Symptoms

One or more of the following errors might occur:

InForm error in the Application event log:
Action: Connect to database

DSN: <pfst45>

Error: SQL Connection Error #1 State: S1000 Message: [Oracle][ODBC][Ora]ORA-12520: TNS:listener could not find available handler for requested type of server

SQL Connection Error #2 State: S1000 Message: [Oracle][ODBC][Ora]ORA-12520: TNS:listener could not find available handler for requested type of server
Error in Oracle Listener Log (default location: <oracle_home>\NETWORK\log\listener.log):
01-SEP-2009 10:24:03 * (CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=Trial1.world)(CID=(PROGRAM=C:\WINDOWS\system32\dllhost.exe)(HOST=RDNEPTUNQ005)(USER=PfUSR_RDNEPTUNQ005))) * (ADDRESS=(PROTOCOL=tcp)(HOST=127.0.0.1)(PORT=2046)) * establish * Trial1.world * 12520

TNS-12520: TNS:listener could not find available handler for requested type of server

Resolution

Increase the value of PROCESSES for the Oracle instance to allow room for the number of connections that will be opened/closed within a 10-minute period.

For more information about the Oracle listener and connection information, see the Oracle MetaLink article 240710.1 on the Oracle website.