The parallel_stmt_critical parameter specifies consumer groups as critical in respect to parallel statements in the plan directive.
When a consumer group is marked as critical, parallel statements issued from these consumer groups bypass the parallel statement queue and execute immediately. Because critical parallel statements bypass the parallel statement queue, the system may encounter more active parallel servers than specified by the PARALLEL_SERVERS_TARGET parameter. Critical parallel statements are allowed to run after the number of parallel servers reaches PARALLEL_MAX_SERVERS, so some critical parallel statements may be downgraded.
The PARALLEL_STMT_CRITICAL column in the DBA_RSRC_PLAN_DIRECTIVES view indicates whether parallel statements are from a consumer group that has been marked critical.