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Outer Join that ran quickly in Oracle 12 is extremely slow in Oracle 19

in SQL Performance (MOSC) 2 commentsAnswered

We have a materialized view definition that joins several tables and other editionable views together. In Oracle 12, this materialized view refreshed quickly.


We upgraded our Oracle 12 instance to Oracle 19 in AWS RDS (19.0.0.0.ru-2021-04.rur-2021-04.r1) and the materialized view refresh would appear to hang.


I looked in v$session_longops and its not exactly stuck... but it appears to be taking an incredibly long time to scan one of the tables involved in the view definition. I also investigated the query plans generated by Oracle 12 vs Oracle 19 and they are incredibly different. Looking for advice on how to proceed - we have workarounds to get the view to work correctly, but we need to understand why this happened so that we can investigate the rest of our solution for potential issues.

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