1     PARALLEL_MAX_SEVERS

网上找到的自理啊如下，当然是过时的，大家看一下即可。

PARALLEL_MAX_SEVERS参数设置并行执行可用的最大进程数量，该参数的缺省值如下得出：

1.当PGA_AGGREGATE_TARGET >0时

       PARALLEL_MAX_SERVERS=(CPU_COUNT x PARALLEL_THREADS_PER_CPU x 10)

2.当PARALLEL_MAX_SERVERS未设置

       PARALLEL_MAX_SERVERS=(CPU_COUNTx PARALLEL_THREADS_PER_CPU x 5)

       缺省设置可能并不足够，通常我们根据最高的并行度（DOP）来设置PARALLEL_MAX_SERVERS参数：

       2x DOP x NUMBER_OF_CONCURRENT_USERS

2     官方说明

PARALLEL_MAX_SERVERS

Property	Description
Parameter type	Integer
Default value	Derived from the values of CPU_COUNT, PARALLEL_THREADS_PER_CPU, and PGA_AGGREGATE_TARGET
Modifiable	ALTER SYSTEM
Range of values	0 to 3599
Real Application Clusters	Multiple instances must have the same value.

这个蛤蟆在12C上也能匹配。

PARALLEL_MAX_SERVERS specifies the maximum number of parallelexecution processes and parallel recovery processes for an instance. As demandincreases, Oracle increases the number of processes from the number created atinstance startup up to this value.

If you set this parameter too low, some queries may nothave a parallel execution process available to them during query processing. Ifyou set it too high, memory resource shortages may occur during peak periods,which can degrade performance

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