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This article introduces the relevant knowledge of "what are the parameters related to database parallelism". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

SQL > show parameters parallel

NAME TYPE VALUE

-

Fast_start_parallel_rollback string LOW

Parallel_adaptive_multi_user boolean TRUE

Parallel_automatic_tuning boolean FALSE

Parallel_execution_message_size integer 2152

Parallel_instance_group string

Parallel_max_servers integer 100

Parallel_min_percent integer 0

Parallel_min_servers integer 0

Parallel_server boolean FALSE

Parallel_server_instances integer 1

Parallel_threads_per_cpu integer 2

Recovery_parallelism integer 0

Fast_start_parallel_rollback: determines the maximum number of processes when performing a parallel fallback.

The value of this parameter means:

False: disable parallel rollback

Number of low:2*cpu slave processes

Number of high:4*cpu slave processes

Parallel_adaptive_multi_user boolean TRUE

Description: enable or disable an adaptive algorithm designed to improve the performance of multiuser environments that use parallel execution. By automatically reducing the parallelism of the request according to the system load

Implement this feature when you start the query. When PARALLEL_AUTOMATIC_TUNING = TRUE, the effect is the best.

Value range: TRUE | FALSE

Default: if PARALLEL_AUTOMATIC_TUNING = TRUE, the value is TRUE; otherwise FALSE

Parallel_automatic_tuning boolean TRUE

Note: if set to TRUE, Oracle will determine the default values for the parameters that control parallel execution. In addition to setting this parameter

You must also set parallelism for the tables in the system.

Value range: TRUE | FALSE

Default value: FALSE

Parallel_execution_message_size integer 4096

Description: specifies the size of messages for parallel execution (parallel query, PDML, parallel recovery and replication). If the value is greater than 2048 or 4096

A larger shared pool is needed. If PARALLEL_AUTOMATIC_TUNING = TRUE

The message buffer will be specified outside the large storage pool.

Value range: 2148-infinity.

Default value: if PARALLEL_AUTOMATIC_TUNING is FALSE, usually 2148; if PARALLEL_AUTOMATIC_TUNING is TRUE, the value is 4096 (depending on the operating system).

Parallel_instance_group string

Description: a cluster database parameter that identifies a group of parallel routines used to generate a large number of parallel execution dependencies. Parallel operations only apply to their INSTANCE_GROUPS

The routines that specify a matching group in the parameter produce a large number of parallel execution dependencies.

Value range: a string that represents the group name.

Default value: group made up of all currently active routines

Parallel_max_servers integer 160

Description: specifies the maximum number of parallel execution servers or parallel recovery processes for a routine. If necessary, the number of query servers allocated when the routine starts will be increased to that number.

Value range: 0-256

Default value: determined by CPU_COUNT, PARALLEL_AUTOMATIC_TUNING and PARALLEL_ADAPTIVE_MULTI_USER

Parallel_min_percent integer 0

Description: specifies the minimum percentage of threads required for parallel execution. Setting this parameter ensures that an error message is displayed when there is no appropriate query slave process available for parallel execution

And the query will not be executed as a result.

Value range: 0-100

The default value is 0, which means that this parameter is not used.

Parallel_min_servers integer 0

Description: specifies the minimum number of query server processes created by Oracle after parallel execution of startup routines.

Value range: 0-PARALLEL_MAX_SERVERS.

Default value: 0

Parallel_server boolean TRUE

Description: you can enable the cluster database option by setting PARALLEL_SERVER to TRUE.

Value range: TRUE | FALSE

Default value: FALSE

Parallel_server_instances integer 2

Description: the number of routines currently configured. It is used to determine the size of the SGA structure, which is determined by the number of routines configured. Setting this parameter correctly will improve SGA.

Memory usage of the Several parameters are calculated with this number.

Value range: any non-zero value.

Default value: 1

Parallel_threads_per_cpu integer 2

Description: indicates the number of processes or threads that a CPU can handle during parallel execution

The parallel adaptive algorithm and load balancing algorithm are optimized. If the computer shows signs of being overloaded when executing a typical query, you should reduce this value.

Value range: any non-zero value.

Default value: depending on the operating system (usually 2)

For example: Parallel Execution for a Session

Parallel execution of sessions, sometimes in order to speed up execution, make full use of multi-CPU resources, such as parallel indexing operations.

To perform certain operations in parallel, you can use alter session statements

ALTER SESSION ENABLE PARALLEL DML | DDL | QUERY

Turn it off with the following statement

Alter session disable parallel DDL | DML | QUERY

Force parallel execution:

ALTER SESSION FORCE PARALLEL DML | DDL | QUERY

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