Short Running Task Worker metric collection status is shown as Down from OMS and Repository monitoring :

From the Management Services and Repository target page, Navigate:

OMS and Repository > Monitoring > All Metrics > select Repository Operations Status

Following query running as sysman shows No Short Running task workers are running, which causes a backlog build up.

SQL> SELECT Decode(task_class_list, 0 , 'Short Running' , 1, 'Long Running ' , 'Unkown') Worker_type,
CASE
WHEN j.job_action IS NULL THEN 'No'
WHEN j.job_action IS NOT NULL THEN 'Yes'
    END AS job_submitted,
    j.state AS job_state,
    w.job_id AS worker_id,
Decode(w.worker_status, 0,'Starting', 1, 'Started', 'Stop Pending') worker_status
    FROM dba_scheduler_jobs j, MGMT_collection_workers w
    WHERE j.job_action(+) = 'EM_TASK.WORKER(' || w.job_id || ');'
   AND w.task_class_list IN ('0','1');

WORKER_TYPE   JOB JOB_STATE        WORKER_ID WORKER_STATU
------------- --- --------------- ---------- ------------
Long Running  Yes SCHEDULED                6 Started
Long Running  Yes SCHEDULED                7 Started

SOLUTION

SQL> show user
USER is "SYSMAN"
SQL> exec mgmt_collection.set_worker_count(0,4);

PL/SQL procedure successfully completed.

SQL> exec mgmt_collection.start_workers();

PL/SQL procedure successfully completed.

SQL> SELECT Decode(task_class_list, 0 , 'Short Running' , 1, 'Long Running ' , 'Unkown') Worker_type,
CASE
WHEN j.job_action IS NULL THEN 'No'
    WHEN j.job_action IS NOT NULL THEN 'Yes'
END AS job_submitted,
    j.state AS job_state,
w.job_id AS worker_id,
    Decode(w.worker_status, 0,'Starting', 1, 'Started', 'Stop Pending') worker_status
FROM dba_scheduler_jobs j, MGMT_collection_workers w
WHERE j.job_action(+) = 'EM_TASK.WORKER(' || w.job_id || ');'
AND w.task_class_list IN ('0','1');  

WORKER_TYPE   JOB JOB_STATE        WORKER_ID WORKER_STATU
------------- --- --------------- ---------- ------------
Short Running Yes SCHEDULED                2 Started
Short Running Yes SCHEDULED                1 Started
Short Running Yes SCHEDULED                3 Started
Short Running Yes SCHEDULED                4 Started
Long Running  Yes SCHEDULED                5 Started
Long Running  Yes SCHEDULED                8 Started

6 rows selected.