Ora-12801 error in parallel query today. Simple query: select/*+parallel(t 16)*/count(1) from A
Look at the official explanation:

ORA-12801: error signaled in parallel query server string

Cause: A parallel query server reached an exception condition.

Action: Check the following error message for the cause, and consult your error manual for the appropriate action.
This explanation is too abstract, I don’t understand the specific reason, finally changed the parallelism to 8:
Select /*+parallel(t 8)*/count(1) from A is OK.

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