Controlling the Degree of Parallelism of Queries
Oracle Database 12.2 introduces a new instance parameter to control the Degree of Parallelism of queries, which involves a containers() construct.
By default, a query involving a containers() construct uses a DOP that is equal to the following value:
In the case of a query in the CDB root, the value is (1 + number of open PDBs).
In the case of a query in an application root, the value is (1 + number of open application PDBs).
If the value of this parameter is less than 65535, the value is used as the DOP for all queries involving containers():
In the session if the value was set at the session level
In the instance if the value was set at the system level
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