Query Execution Plan Changed After UpgradingDG4DRDA From 11.2.0.3 To 11.2.0.4 Causing Increased Execution Times (Doc ID 1681234.1)

Last updated on DECEMBER 11, 2014

Applies to:

Oracle Database Gateway for DRDA - Version 11.2.0.4 to 12.1.0.2 [Release 11.2 to 12.1]
Information in this document applies to any platform.

Symptoms

The query execution plan for a particular query against several DB2 tables changed after upgrading the Database Gateway for DRDA (DG4DRDA) from 11.2.0.3 to 11.2.0.4.
After the gateway upgrade the SQL against the DB2 tables had a different execution plan -
- In 11.2.0.3, the execution plan sent a complete query to DB2 for all the tables and results were returned in 30 minutes
- In 11.2.0.4, the execution plan causes queries against individual DB2 tables on the DB2 side. There is then join made on the Oracle side of the individual table results. Because the underlying DB2 tables are large, the query now runs for over 4 hrs.

- In 12.1.0.1 and 12.1.0.2 you can receive the ORA-28501: communication error on heterogeneous database link 

Cause

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