ORA-00020 reported after upgrading the database to 12c

ORA-00020 reported after upgrading the database to 12c , without any changes in the application. We notice a sudden increase in number of background process(pxxx).

CAUSE

 From 12c parallel_min_servers default value calculation has been changed to CPU_COUNT * PARALLEL_THREADS_PER_CPU * 2 from 0. for more details on this, refer to the document:

(Doc ID 1678111.1) PARALLEL_MIN_SERVERS Does Not Limit The Number Of Parallel Processes At Startup in 12c

SOLUTION

 1. Check the current value of parallel_min_server.

show parameter parallel_min_servers

 2. Reduce the parallel_min_servers to a realistic value.

alter system set parallel_min_servers=<value> scope=both;

 This should avoid the ORA-20 caused by this increased number of background processes

Note: You cannot reduce the value for parallel_min_servers in 12.1.0.1, to do install patch 17452799 then reduce the value. This patch is included in 12.1.0.2.