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poor sqlperformance after migration from 11g to 19.10 Why?

edited Apr 13, 2022 8:34AM in SQL Performance (MOSC) 7 commentsAnswered ✓

Hello,

we did a Migration from 11g to Oracle 19.10 recently. Now lot of the querys run very poor on the new machine. The CBO decides mostly to use "hash_join" if tables are joined, the old machine used "nested loops" with index range scans instead. In our case "nl with indexes" gives the better performance on both systems.

We also ran "dbms_stats" to have up-to-date statistics on both systems.

No i have to use on the new machine in a lot of querys performance hints to tell the CBO not to use "hash_joins". What's the reason does anybody know?

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