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Oracle Parallel Parameters

原创 Linux操作系统 作者:chncaesar 时间:2013-11-12 10:59:46 0 删除 编辑
Specifies whether or not automatic degree of Parallelism,statement queuing, and in-memory parallel execution will be enabled. MANUAL is the default, which disables automatic degree of parallelism, statement queuing, and in-memory parallel execution. AUTO enables automatic degree of parallelism, statement queuing, and in-memory parallel execution.

This parameter specifies the minimum execution time a statement should have before the statement is considered for automatic degree of parallelism. By default, this is set to 10 seconds. Automatic degree of parallelism is only enabled if PARALLEL_DEGREE_POLICY is set to AUTO or LIMITED. The default is AUTO.

With automatic degree of parallelism, Oracle automatically decides whether or not a statement should execute in parallel and what degree of parallelism the statement should use. The optimizer automatically determines the degree of parallelism for a statement based on the resource requirements of the statement. However, the optimizer will limit the degree of parallelism used to ensure parallel server processes do not flood the system. This limit is enforced by PARALLEL_DEGREE_LIMIT.
CPU - The maximum degree of parallelism is limited by the number of CPUs in the system. The formula used to calculate the limit is PARALLEL_THREADS_PER_CPU * CPU_COUNT * the number of instances available (by default, all the opened instances on the cluster but can be constrained using PARALLEL_INSTANCE_GROUP or service specification). This is the default.

specifies the maximum number of parallel execution processes and parallel recovery processes for an instance.

This parameter specifies the number of parallel server processes allowed to run parallel statements before statement queuing is used. 
When PARALLEL_DEGREE_POLICY is set to AUTO, statements that require parallel execution are queued if the number of parallel processes currently in use on the system equals or is greater than PARALLEL_SERVERS_TARGET. This is not the maximum number of parallel server processes allowed on a system (that is controlled by PARALLEL_MAX_SERVERS). However, PARALLEL_SERVERS_TARGET and parallel statement queuing is used to ensure that each statement that requires parallel execution is allocated the necessary parallel server resources and the system is not flooded with too many parallel server processes.

This parameter specifies the number of processes to be started in a single instance that are reserved for parallel operations. Processes started using PARALLEL_MIN_SERVERS do not exit until the database is shut down. This way, when a query is issued, the processes are likely to be available.

Default value is 0. Setting this parameter to values other than 0 (zero) causes Oracle Database to return an error when the requested DOP cannot be satisfied by the system at a given time. For example, if you set PARALLEL_MIN_PERCENT to 50, which translates to 50 percent, and the DOP is reduced by 50 percent or greater because of the adaptive algorithm or because of a resource limitation, then Oracle Database returns ORA-12827: insufficient parallel query slaves available.

Parallel execution requires memory resources in addition to those required by serial SQL execution. Additional memory is used for communication and passing data between query server processes and the query coordinator.Oracle Database allocates memory for query server processes from the shared pool. 

This parameter specifies whether a SQL statement executed in parallel is restricted to a single instance in an Oracle RAC environment.

The PARALLEL_IO_CAP_ENABLED parameter is deprecated. It is retained for backward compatibility only. It is replaced by the PARALLEL_DEGREE_LIMIT parameter when set to IO.

The parameter describes the number of parallel execution processes or threads that a CPU can handle during parallel execution.

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