ANSI SQL Statement Running Slow in 12C
(Doc ID 2255117.1)
Last updated on MARCH 18, 2022
Applies to:
Oracle Database Cloud Schema Service - Version N/A and laterOracle Database Backup Service - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Cloud Service - Version N/A and later
Oracle Database - Enterprise Edition - Version 12.1.0.2 and later
Information in this document applies to any platform.
Symptoms
- After upgrading the database from 11.2.0.4 to 12.1.0.2, the ANSI version of SQL statements take long time to complete
- Optimizer chooses inefficient plan in 12c for SQLs having ANSI joins and scalar subqueries.
- The non-ANSI version of the same SQL statements take only less than a second to complete with following plans:
- Setting OPTIMIZER_FEATURES_ENABLE = '11.2.0.4' resolves the issue with performance for the ANSI query.
- Setting _OPTIMIZER_UNNEST_SCALAR_SQ to FALSE also gives good plan but push predicate does not happen.
Changes
Database upgrade from 11.2 to 12c including 12.2 and 18.1.
Cause
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In this Document
| Symptoms |
| Changes |
| Cause |
| Solution |
| References |