Dictionary Queries Run Slowly in 12C Pluggable Databases
(Doc ID 2033658.1)
Last updated on MARCH 18, 2022
Applies to:
Oracle Database - Enterprise Edition - Version 12.1.0.1 to 12.1.0.1 [Release 12.1]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
Oracle Database Cloud Service - Version N/A and later
Information in this document applies to any platform.
Symptoms
- Following migration from Database from 11g to a pluggable database (PDB) on Oracle 12c, some dictionary queries involving DBA_CONSTRAINTS, DBA_SYNONYMS, DBA_TAB_COLUMNS etc are running very slowly.
- The same SQL statements execute fine in a non-pluggable 12c environment and pre-12c
- Plans in the problem environment are different to the good environment (non-CDB).
- The PDB plan selects from common view in Container database (CDB) X$COMVW$ (and derivatives) only.
- In the non-CDB 12c database, plan does not select from X$COMVW$, but accesses base tables only.
- The Plan in the bad environment (12c Pluggable Database) is similar to:
Changes
Running on a pluggable database (migration from an earlier release is not necessary)
Cause
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In this Document
| Symptoms |
| Changes |
| Cause |
| Solution |
| References |