SQL & PL/SQL

I'm trying to create an index on a large partitioned table. I started with a simple CREATE INDEX which took 5 hours.

In my next attempt, I tried below steps:

1. Create index as UNUSABLE
2. Loop through all the subpartitions and rebuild index with PARALLEL 8 NOLOGGING using below code.

CREATE OR REPLACE PROCEDURE  sp_rebuild_indx_partition (i_indexname VARCHAR2) AS
BEGIN
    FOR sp_idx IN ( SELECT disp.index_name, disp.subpartition_name
    FROM dba_ind_subpartitions disp
    WHERE EXISTS (SELECT 1 
                    FROM dba_tab_partitions dtp 
                    WHERE dtp.table_name = '<TABLE_NAME>' 
                    AND disp.partition_name = dtp.partition_name)
    AND disp.index_name = i_indexname
    AND disp.status = 'UNUSABLE')
    LOOP
        EXECUTE IMMEDIATE 'ALTER INDEX '||sp_idx.index_name||' REBUILD SUBPARTITION '||sp_idx.subpartition_name||' PARALLEL 8 NOLOGGING';
    END LOOP;
END;

The second attempt took almost the same time as initial attempt.

I checked the parallel parameters and noticed parallel execution might not be enabled. My knowledge on understanding these parameters are limited. Can someone help me understand if I'm doing something wrong or if the parameters need to be altered to take advantage of the parallel execution?

NAME                            TYPE    VALUE  
------------------------------- ------- ------ 
_parallel_broadcast_enabled     boolean TRUE   
awr_pdb_max_parallel_slaves     integer 10     
containers_parallel_degree      integer 65535  
fast_start_parallel_rollback    string  LOW    
max_datapump_parallel_per_job   string  50     
optimizer_ignore_parallel_hints boolean FALSE  
parallel_adaptive_multi_user    boolean FALSE  
parallel_degree_limit           string  CPU    
parallel_degree_policy          string  MANUAL 
parallel_execution_message_size integer 16384  
parallel_force_local            boolean FALSE  
parallel_instance_group         string         
parallel_max_servers            integer 0      
parallel_min_degree             string  1      
parallel_min_percent            integer 0      
parallel_min_servers            integer 0      
parallel_min_time_threshold     string  AUTO   
parallel_servers_target         integer 0      
parallel_threads_per_cpu        integer 1      
recovery_parallelism            integer 0 

Using:

Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production

Windows 11