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Oracle® Database Reference
11g Release 2 (11.2)

E40402-14
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PARALLEL_MAX_SERVERS

Property Description
Parameter type Integer
Default value PARALLEL_THREADS_PER_CPU * CPU_COUNT * concurrent_parallel_users * 5
Modifiable ALTER SYSTEM
Range of values 0 to 3600
Oracle RAC Multiple instances can have different values.

Note:

This parameter applies to parallel execution in exclusive mode as well as in a Real Application Clusters environment.

PARALLEL_MAX_SERVERS specifies the maximum number of parallel execution processes and parallel recovery processes for an instance. As demand increases, Oracle Database increases the number of processes from the number created at instance startup up to this value.

In the formula, the value assigned to concurrent_parallel_users running at the default degree of parallelism on an instance is dependent on the memory management setting. If automatic memory management is disabled (manual mode), then the value of concurrent_parallel_users is 1. If PGA automatic memory management is enabled, then the value of concurrent_parallel_users is 2. If global memory management or SGA memory target is used in addition to PGA automatic memory management, then the value of concurrent_parallel_users is 4.

If you set this parameter too low, then some queries may not have a parallel execution process available to them during query processing. If you set it too high, then memory resource shortages may occur during peak periods, which can degrade performance.

See Also:

Oracle Database Performance Tuning Guide for more information on tuning parallel execution