Parallel_Degree_Policy=AUTO does not control recursive SQL generated for the purposes of referential integrity
(Doc ID 2042044.1)
Last updated on FEBRUARY 27, 2019
Applies to:Oracle Database - Enterprise Edition - Version 220.127.116.11 to 18.104.22.168 [Release 11.2 to 12.1]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.
When PARALLEL_DEGREE_POLICY is set to AUTO the optimizer computes the DOP for user queries. Even if the optimizer decides to run a query in serial mode the recursive queries used to check referential integrity can run in parallel depending on the table's PARALLEL setting. If there are many of these queries this can generate a large number of parallel slaves. This is similar to document “Some Statements Unexpectedly Run in Parallel With Auto DOP (PARALLEL_DEGREE_POLICY = AUTO or LIMITED) (Doc ID 1643540.1)”, but this is related to bug 9728438, whereas the behavior described in this document is expected.
Recursive SQL statements used to check referential integrity use the target table's PARALLEL setting
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