Five Best Practices for Setting Dispatchers on Shared Connections

Posted in: Oracle, Technical Track

In this post I’d like to present five best practices/tips for setting dispatchers for database shared connections:

Setting DISPATCHERS on a database resident connection pool (DRCP).

1. Set local_listener on both instances of the database

alter system set LOCAL_LISTENER=”(address=(protocol=tcp)(port=1521)(host=yourhost))” scope=both sid=’instance_name’;
Ref: Shared Server: Dispatchers Are Not Registered With Listener (Doc ID 465881.1)

2. Dispatchers parameter should be set to utilize the VIP name of the host

alter system set dispatchers='(address=(protocol=tcp)(host=node1-vip))(dispatchers=2)’ scope=both sid=’instance_name’;
Ref: How To Configure Shared Server Dispatchers For RAC Environment (Doc ID 578524.1)

3. Set dispatchers count appropriately considering the number of sessions expected to connect to the database

A general rule of thumb is that one dispatcher can handle 50 shared server connections with minimal performance impact.
Ref: Shared Server Only: TNS-12518, TNS-12564 and TNS-12602 Errors at Connect Time (Doc ID 1539104.1)

4. You can use arguments with the dispatchers parameter for closer control of how the shared server sessions are used

SESSIONS: Determines the max sessions allowed for each dispatcher.
CONNECTIONS: The maximum number of network connections to allow for each dispatcher.

5. Set shared_servers parameter to control the total number of shared servers spawned by the database

shared_servers set to 1 –> This will enable shared server sessions on the database.
max_shared_servers  –> Specifies the maximum number of shared servers that can run simultaneously.
shared_server_sessions  –> Specifies the total number of shared server user sessions that can run simultaneously. Setting this parameter enables to reserve user sessions for dedicated servers.
Ref: Automatic Shared Server Configuration (Doc ID 265931.1)

I hope this information is helpful. If you have any questions or thoughts, please leave them in the comments. See you next post!

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About the Author

Lead Database Consultant
Well known in the Oracle community in Latin America and Europe where he participates regularly in technology events, Matheus is actually the youngest Oracle ACE Director in the world. Lead Database Consultant at Pythian, Matheus is a Computer Scientist by PUCRS and has been working as an Oracle DBA for the last 10 years.

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