Five Best Practices for Setting Dispatchers on Shared Connections

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

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.
Ref: https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/DISPATCHERS.html#GUID-DCBCCF94-8A73-4805-9138-412DA413FC7C

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!