Memory Management for Shared Server

 Shared server requires some user global area (UGA) in either the shared pool or large pool. For installations with a small number of simultaneous sessions, the default sizes for these system global area (SGA) components are generally sufficient. However, if you expect a large number of sessions for your installation, you may have to tune memory to support shared server.

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Enabling Shared Server

Shared server is enabled by setting the SHARED_SERVERS initialization parameter to a value greater than 0. The other shared server initialization parameters need not be set.

• Set shared server dynamically by setting the SHARED_SERVERS initialization parameter to a nonzero value with the ALTER SYSTEM statement.

• Set the SHARED_SERVERS initialization parameter to a nonzero value at database startup by including it in the initialization parameter file.

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Because shared server requires at least one dispatcher in order to work, a dispatcher is brought up even if no dispatcher has been configured. Dispatchers are discussed in "Configuring Dispatchers".

• About Determining a Value for SHARED_SERVERS
  The SHARED_SERVERS initialization parameter specifies the minimum number of shared servers that you want created when the instance is started. After instance startup, Oracle Database can dynamically adjust the number of shared servers based on how busy existing shared servers are and the length of the request queue.
• Decreasing the Number of Shared Server Processes
  You can decrease the minimum number of shared servers that must be kept active by dynamically setting the SHARED_SERVERS parameter to a lower value. Thereafter, until the number of shared servers is decreased to the value of the SHARED_SERVERS parameter, any shared servers that become inactive are marked by PMON for termination.

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• Limiting the Number of Shared Server Processes
  The MAX_SHARED_SERVERS initialization parameter specifies the maximum number of shared servers that can be automatically created by PMON. It has no default value.
• Limiting the Number of Shared Server Sessions
  The SHARED_SERVER_SESSIONS initialization parameter specifies the maximum number of concurrent shared server user sessions.
• Protecting Shared Memory
  The CIRCUITS initialization parameter sets a maximum limit on the number of virtual circuits that can be created in shared memory. This parameter has no default. If it is not specified, then the system can create circuits as needed, limited by the DISPATCHERS initialization parameter and system resources.

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