Database Memory & 4030/4031 (MOSC)

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Abnormal auto SQL tuning task behaviours

edited Feb 10, 2022 3:02PM in Database Memory & 4030/4031 (MOSC) 6 commentsAnswered

Hi

After upgrading from 12c to 19c (currently 19.4), I have high memory load every night when auto SQL tuning task runs :

As you can see on monitoring, DB usage is about 5/6G during the day, and all remaining memory is used when auto task is running at 22:00.

If I try to limit PGA_AGGREGATE_LIMIT, I get an ORA-04036 (PGA memory used by the instance exceeds PGA_AGGREGATE_LIMIT) on DBMS_STATS_ADVISOR session. And if I do not limit PGA, I get a server memory overload. Of course I could increase server RAM but 15G seems far than enough for a 5G normal usage. Then before I'd like to know if this a normal behaviour from auto task.. It's like it's trying to sample all requests recorded at the same time, and of course using all available memory as PGA. This never happened before on oracle 12c.

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