2018年2月14日 688点热度 0人点赞 0条评论
Property Description
Parameter type Integer
Default value PARALLEL_THREADS_PER_CPU * CPU_COUNT * concurrent_parallel_users * 5
Range of values 0 to 3600
Oracle RAC Multiple instances can have different values.

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.【译文:在这个公式中,数据库实例默认并发度情况下,分配给concurrent_parallel_users的值取决于内存管理机制。如果关闭了自动内存管理模式即手动模式下,concurrent_parallel_users=1。如果PGA自动内存管理模式打开,concurrent_parallel_users=2。如果除PGA自动内存模式打开以外,还打开了全局内存管理模式或SGA内存做了设置,concurrent_parallel_users=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.【译文:如果设置过高,在峰值时段可能会导致内存资源不足,这会降低性能】