Parallel Operations and Services in Oracle RAC

Yesterday, one of the members on Oracle Community forum posted that his query was not executing in parallel.
The query he used:

SELECT /*+ PARALLEL(r) */
r.c1 , r.c2
FROM table1 r

This was his output from show parameter parallel

SQL> show parameter parallel

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
fast_start_parallel_rollback         string      LOW
parallel_adaptive_multi_user         boolean     TRUE
parallel_automatic_tuning            boolean     FALSE
parallel_degree_limit                string      CPU
parallel_degree_policy               string      MANUAL
parallel_execution_message_size      integer     4096
parallel_force_local                 boolean     FALSE
parallel_instance_group              string      op015pdb01
parallel_io_cap_enabled              boolean     FALSE
parallel_max_servers                 integer     192
parallel_min_percent                 integer     0
parallel_min_servers                 integer     8
parallel_min_time_threshold          string      AUTO
parallel_server                      boolean     TRUE
parallel_server_instances            integer     2
parallel_servers_target              integer     192
parallel_threads_per_cpu             integer     2
recovery_parallelism                 integer     64

It turned out that the database he was using is Oracle RAC and what I found interesting is that parallel_instance_group was set to op015pdb01. Continue reading