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Parallel query slowered query performance

edited Aug 18, 2020 5:06AM in Database Administration (MOSC) 16 commentsAnswered

Hi,

since upgrading our RAC DB from 12.2. to 19c I'm facing following issue:

A specific SQL joins views, mviews and some tables. From statistics It runs with 8 parallel processes (it matches with CPU count, parallel_min_servers is 8, parallel_max_servers is 80).

The problem is that it causes many concurency waits from parallel processes (Pxxxx).

There are also many other queries running in parallel, but there are no performance degradation or high concurency waits of Pxxx processes observed in AWR/ASH.

I could resolve this by setting the /+ NOPARALLEL */ hint in this specific SQL. But I'm just wonder why this problem cames up with 19c.

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