MERGE Statement poor performance due to use of NESTED LOOPS instead HASH JOIN OUTER because of multiple filter predicates
(Doc ID 2276300.1)
Last updated on AUGUST 08, 2019
Applies to:Oracle Database - Enterprise Edition - Version 188.8.131.52 to 184.108.40.206 [Release 11.2 to 12.2]
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Information in this document applies to any platform.
Merge statement cannot use HASH JOIN OUTER when there are multiple filter predicates in the join clause. There is an OR operator between those predicates.
Nested loop join is used instead which makes the statement never ending.
The problem manifests as well with UPDATE and DELETE.
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