1. Database Reference
  2. Initialization Parameters
  3. Initialization Parameters
  4. PARALLEL_MAX_SERVERS

1.249 PARALLEL_MAX_SERVERS

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.
Property Description

Parameter type

Integer

Default value

PARALLEL_THREADS_PER_CPU * CPU_COUNT * concurrent_parallel_users * 5

Modifiable

ALTER SYSTEM

Modifiable in a PDB

Yes

Range of values

0 to 32767

Basic

No

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.

The number of concurrent parallel users running at default degree of parallelism on an instance depends on the memory initialization parameter settings for the instance. For example, if the MEMORY_TARGET or SGA_TARGET initialization parameter is set, then the number of concurrent_parallel_users = 4. If neither MEMORY_TARGET or SGA_TARGET is set, then PGA_AGGREGATE_TARGET is examined. If a value is set for PGA_AGGREGATE_TARGET, then concurrent_parallel_users = 2. If a value is not set for PGA_AGGREGATE_TARGET, then concurrent_parallel_users = 1.

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.

Note:

The database system always reserves a certain number of reserved processes.

The default value of the PARALLEL_MAX_SERVERS initialization parameter is set to the lower of these two values:

  • The default value of PARALLEL_MAX_SERVERS determined using the calculation in the table above

  • The value of the PROCESSES initialization parameter minus the number of reserved processes

When the PARALLEL_MAX_SERVERS parameter is set to a value lower than the value in the table above, the lower default value enables the database to start service processes and allows user processes to connect to the database.

The default value for PARALLEL_MAX_SERVERS for a PDB is determined using the calculation in the table above with the PDB’s CPU_COUNT value.

See Also:

Oracle Database SQL Tuning Guide for more information about parallel execution