Parallelism analyzing

set :

set timi on
set autot on

to chose the difference betwee:

select count(*) from all_users au;

 and

select /*+ parallel (au,10) */ count(*) from all_users au;

some useful information:

select * from V$PX_SESSION;

SELECT NAME, VALUE FROM GV$SYSSTAT
WHERE UPPER (NAME) LIKE '%PARALLEL OPERATIONS%'
OR UPPER (NAME) LIKE '%PARALLELIZED%' OR UPPER (NAME) LIKE '%PX%';

SELECT * FROM V$PX_PROCESS;

SELECT * FROM V$PX_PROCESS_SYSSTAT;

parameter to reduse/increase parallelism in Oracle is PARALLEL_MAX_SERVERS.