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Query behavior after migrating from 12.1 to 19c

edited Apr 28, 2021 9:49PM in Database Administration (MOSC) 9 comments

My organization has experienced some severe SQL Performance degradation after migrating from an Exadata x5-1 running RDBMS 12.1.0.2 to an Exadata x8m running 19.10 RDBMS. The queries are generated from OBIEE and are quite complex. Because of this, we have no control on changing the queries that are created.

90 to 95% of our BI queries are processing just as good as the old Exadata system. We have a few queries that do not perform as well with one query that never finishes on 19.10 compared to 48 seconds in 12.1.0.2. We have tried many different SQL tuning attempts creating indexes/tuning profiles and different permutations of optimizer_features_enable parameter from 19.1 to 12.1.0.2 as well as cursor_sharing=FORCE vs EXACT with limited success. I've tried to use tuning profiles as a last resort as they can become a maintenance headache. 

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