188.8.131.52 PDB (FROM 184.108.40.206) USES UNWANTED/SLOW PARALLEL QUERY EVEN WHEN DISABLED ON SESSION LEVEL
(Doc ID 2072729.1)
Last updated on MAY 19, 2022
Applies to:Oracle Database - Enterprise Edition - Version 220.127.116.11 and later
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.
upgraded an application from db 18.104.22.168 to 22.214.171.124. Now we notice very strange and highly unwanted behavior that strongly delays/slows queries that were previously executing fast. Investigation has finally shown that dictionary queries keep on executing parallel (SQL monitoring show PX plans) despite disabling parallel query/dml/ddl on session level and despite adding no_parallel hints to the query. The only thing that prevents parallel execution is setting parallel_max_servers to zero.
This only occurs with upgraded and next plugged in databases. With a fresh PDB (created in 12c, so no 11g history) from PDB$SEED the disable parallel query does work.
To view full details, sign in with your My Oracle Support account.
Don't have a My Oracle Support account? Click to get started!
In this Document