how to use dbms_scheduler to run the job every 30 minutes - oracle

Question

I am using oracle DB , now as i am monitoring the performance of oracle DB which is connected to my java application , so rite now i have to monitor the count of active connections in DB at regular intervals lets say after every 30 minutes below is the query which return me the count of active users along with there name and count
select osuser, count(osuser) as active_conn_count
from v$session
group by osuser
order by active_conn_count desc
now please advise how can i make an schedule a job in scheduler in oracle DB itself that will get triggered at every 30 minutes .

Answer 1

I would suggest to keep your statistics in a table (say my_log_table), in that case schedule would look something like this:
begin
DBMS_SCHEDULER.CREATE_JOB (
job_name => 'keep_stats',
job_type => 'PLSQL_BLOCK',
job_action => 'begin insert into my_log_table (mUser,mCnt) (select osuser, count(osuser) as active_conn_count from v$session group by osuser order by active_conn_count desc);commit;end;',
start_date => timestamp '2016-11-07 19:00:00',
repeat_interval => 'FREQ=MINUTELY;INTERVAL=30;',
enabled => TRUE);
end;

Answer 2

There are pretty much examples about dbms_scheduler. It's easy to submit a recurring job. But actually you do not need to do that! Oracle already stores tons of data about database performance, it will be easier and much more accurate to use these statistics.
Take a look at the active_session_history over here.
Hope this is what you are looking for.

Answer 3

repeat_interval => 'FREQ=HOURLY; BYMINUTE=0,30; BYSECOND=0 ', -

Answer 4

First, you create a schedule.
dbms_scheduler.create_schedule( schedule_name => 'EVERY_1ST_SATURDAY'
, repeat_interval => 'FREQ=MONTHLY;INTERVAL=1;BYDAY=1 SAT;BYHOUR=2;BYMINUTE=0'
, start_date => SYSTIMESTAMP
, comments => '1st Saturday of the month 2am.'
);
Optionally, you create a program:
dbms_scheduler.create_program( program_name => 'GATHER_SCHEMA_STATS'
, program_type => 'STORED_PROCEDURE'
, program_action => 'dbms_stats.GATHER_SCHEMA_STATS'
, number_of_arguments => 1
, enabled => FALSE
, comments => 'Gather schema''s stats (e.g. FRAMEWORK''s)'
);
... grant access to it:
GRANT execute ON sys.GATHER_SCHEMA_STATS TO framework;
... and parameters for it:
DBMS_SCHEDULER.define_program_argument ( 'GATHER_SCHEMA_STATS', 1 , 'ownname', 'VARCHAR2', 'FRAMEWORK' );
Secondly, you create a job:
DBMS_SCHEDULER.CREATE_JOB ( job_name => 'FRAMEWORK.GATHER_FRAMEWORK_STATS_JOB1'
, program_name => 'SYS.GATHER_SCHEMA_STATS'
, schedule_name => 'SYS.EVERY_1ST_SATURDAY'
, enabled => TRUE
, auto_drop => FALSE
, comments => 'Gather FRAMEWORK''s stats on 1st Saturday of the month.'
);