Oracle如何禁止并行

PURPOSE

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To explain how to disable Parallel Execution on Session/System level

 

 

SCOPE & APPLICATION

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DBA's and Support Analysts

 

 

Disable Parallel Execution on Session Level

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To disable PX on session level you can use the 

following three commands together.

 

1.) ALTER SESSION DISABLE PARALLEL DML;

2.) ALTER SESSION DISABLE PARALLEL DDL;

3.) ALTER SESSION DISABLE PARALLEL QUERY;

 

A SQL statement with a parallel hint would  run in parallel if you use

"ALTER SESSION DISABLE PARALLEL DML" that is expected.

Hints overrides alter session settings.  

 

 

Disable Parallel Execution on System Level

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To disable PX on the database level you have two possibilities.

 

1.)  Set  PARALLEL_MIN_SERVERS = 0

          PARALLEL_MAX_SERVERS = 0

          PARALLEL_AUTOMATIC_TUNING = FALSE;  

     and restart the database.

     In 10g and higher versions you can change this parameter with a ALTER SYSTEM command and 

     you do not have to restart the database.

     PARALLEL_AUTOMATIC_TUNING is deprecated in 10.1 and the default is  FALSE.   

 

2.)  Without restarting the database.

     Set the degree of all tables and indices to 1.

     You can use the command

     ALTER TABLE <TABLE_NAME> PARALLEL 1;

     ALTER INDEX <INDEX_NAME> PARALLEL 1,

 

     In the second case you can not be 100% sure that a statement runs in parallel.

     All statement which have parallel hints are still run in parallel, because

     the PARALLEL hint overrides the degree of the objects.

REFERENCES：DISABLE PARALLEL EXECUTION ON SESSION/SYSTEM LEVEL (文档 ID 235400.1)