Oracle数据库并行操作，特别是在RAC环境，一定程度上能够提升数据库的性能，所以对相关的初始化参数的了解是必要的，这篇文章将根
oracle数据库并行操作，特别是在rac环境，一定程度上能够提升数据库的性能，所以对相关的初始化参数的了解是必要的，这篇文章将根据实际的案例讨论oracle数据库的部分并行参数。
Oracle数据库相关的并行参数：
SQL> show parameter parallel
NAME TYPE VALUE
------------------------------------ ---------------------- --------------------
fast_start_parallel_rollback string LOW
parallel_adaptive_multi_user boolean TRUE
parallel_automatic_tuning boolean FALSE
parallel_degree_limit string CPU
parallel_degree_policy string MANUAL
parallel_execution_message_size integer 16384
parallel_force_local boolean FALSE
parallel_instance_group string
parallel_io_cap_enabled boolean FALSE
parallel_max_servers integer 135
parallel_min_percent integer 0
NAME TYPE VALUE
------------------------------------ ---------------------- --------------------
parallel_min_servers integer 0
parallel_min_time_threshold string AUTO
parallel_server boolean FALSE
parallel_server_instances integer 1
parallel_servers_target integer 64
parallel_threads_per_cpu integer 2
recovery_parallelism integer 0
下面是实际Oracle RAC环境下，Oracle并行参数的设置，，我们将优先讨论这些参数：
*.parallel_adaptive_multi_user=FALSE
*.parallel_execution_message_size=16384
*.parallel_max_servers=240
*.parallel_min_servers=0
*.parallel_threads_per_cpu=1
PARALLEL_ADAPTIVE_MULTI_USER
PropertyDescription
Parameter type Boolean
Default value true
Modifiable ALTER SYSTEM
Range of values true | false
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PARALLEL_ADAPTIVE_MULTI_USER, when set to true, enables an adaptive algorithm designed to improve performance in multiuser environments that use parallel execution. The algorithm automatically reduces the requested degree of parallelism based on the system load at query startup time. The effective degree of parallelism is based on the default degree of parallelism, or the degree from the table or hints, divided by a reduction factor.ITPUB个人空间T(k k(gsnA2i
当PARALLEL_ADAPTIVE_MULTI_USER参数设置为TRUE，启用设计的适当算法，在多用户环境下使用并行执行提升性能。这个算法基于查询开始时的系统负载自动减少请求的并行度。有效的并行度是基于默认的并行度，或者来自表或HINT的并行度，通过减少系数进行分割。
The algorithm assumes that the system has been tuned for optimal performance in a single-user environment.
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Tables and hints use the default degree of parallelism.ITPUB个人空间G8["q^8VxV2B%Sd
表和HINT使用默认的并行度。
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PARALLEL_MAX_SERVERS
PropertyDescription
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.
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Note:
This parameter applies to parallel execution in exclusive mode as well as in a Real Application Clusters environment.
