UPDATE SQL statement has poor performance

Question

Hi All,
We have setup regular run background process,setup to "throttle"  user submitted
Batch Requests to Batch Processing System.  Purpose of this "Throttle" DB level background
process  (submitted using DBMS_SCHEDULER)  to check for currently active Requests and
then accordingly (based on prevailing System Load)   inject new requests for Batch Request accordingly.
This background process is scheduled to run every minute.
We find that UPDATE statement below performs well when Table being updated (FRM_BPF_REQUEST)
even when Table has upto 1 million rows.  (Expected Production volume)  UPDATE takes only few seconds  (< 10 secs)
at most to execute
However, we find that when there is a burst of INSERTS happening to  same Table  (FRM_BPF_REQUEST)
via another database session,  UPDATE statement suffers with severe degradation.  Same UPDATE which used
to perform  in matter of few seconds, takes upto  40 minutes when heavy INSERTS are happenning to
Table.  We are trying to understand why Performance gets severely degraded when INSERTS are heavy on the Table,
Any thoughts or insights into issue would be greatly appreciated.
We are using Oracle DB 11.2.0.3.4  (on Linux)
CREATE OR REPLACE PROCEDURE BPF_DISPATCH_REQUEST_SP(V_THROTTLE_SIZE NUMBER DEFAULT 600) AS
--    Change History
--001 -Auro    -10/09/2013  -Initial Version
--    v_throttle_size    NUMBER DEFAULT 600;
      v_active_cnt         NUMBER DEFAULT 0;
      v_dispatched_cnt   NUMBER DEFAULT 0;
    v_start_time    TIMESTAMP := SYSTIMESTAMP;
    v_end_time    TIMESTAMP;
        v_subject_str   VARCHAR2(100) := '';
        v_db_name       VARCHAR2(20) := '';
  BEGIN
    -- Determine Throttle Size
    SELECT THROTTLE_SIZE
    INTO   v_throttle_size
    FROM   FRM_BPF_REQUEST_CONTROL;
    -- Determine BPF Active Request Count
    SELECT COUNT(*)
    INTO   v_active_cnt
    FROM   FRM_BPF_REQUEST
    WHERE  STATUS IN('rm_pending','rm_ready','processing','worker_ready','failed','dependency_failed','recover_ready');
    IF v_active_cnt < v_throttle_size THEN
        UPDATE FRM_BPF_REQUEST
        SET    STATUS='dispatched'
        WHERE  ID IN (
                SELECT ID FROM (
               SELECT ID
               FROM   FRM_BPF_REQUEST
               WHERE  STATUS='new'
               ORDER BY ID
                ) WHERE ROWNUM <= (v_throttle_size - v_active_cnt)
        v_dispatched_cnt := SQL%ROWCOUNT;
        COMMIT;
    END IF;
     v_end_time := SYSTIMESTAMP;
    INSERT INTO FRM_BPF_REQUEST_DISPATCH_LOG
    VALUES (
        v_start_time,   
        v_active_cnt,
        v_dispatched_cnt,
        v_end_time,
        NULL
    COMMIT;
    EXCEPTION
              WHEN OTHERS THEN
            ROLLBACK;
         v_end_time := SYSTIMESTAMP;
        INSERT INTO FRM_BPF_REQUEST_DISPATCH_LOG
        VALUES (
            v_start_time,   
            v_active_cnt,
            v_dispatched_cnt,
            v_end_time,
            NULL
        COMMIT;
            SELECT ORA_DATABASE_NAME
        INTO   v_db_name
        FROM   DUAL;
               v_subject_str := v_db_name||' DB: Fatal Error in BPF Request Dispatch Process';
        -- Alert Support                   
            DBA_PLSQL.SEND_MAIL(P_RECIPIENTS     => '[email protected]',
                                    P_CC         => '[email protected]',
                                        P_BCC         => '[email protected]',
                                        P_SUBJECT         => v_subject_str,
                                        P_BODY         => SUBSTR(SQLERRM, 1, 250));
END;
show errors
Thanks
Auro

Answer 1

What the heck is this:
  EXCEPTION
              WHEN OTHERS THEN
            ROLLBACK;
         v_end_time := SYSTIMESTAMP;
        INSERT INTO FRM_BPF_REQUEST_DISPATCH_LOG
        VALUES (
            v_start_time,   
            v_active_cnt,
            v_dispatched_cnt,
            v_end_time,
            NULL
        COMMIT;
            SELECT ORA_DATABASE_NAME
        INTO   v_db_name
        FROM   DUAL;
               v_subject_str := v_db_name||' DB: Fatal Error in BPF Request Dispatch Process';
        -- Alert Support                   
            DBA_PLSQL.SEND_MAIL(P_RECIPIENTS     => '[email protected]',
                                    P_CC         => '[email protected]',
                                        P_BCC         => '[email protected]',
                                        P_SUBJECT         => v_subject_str,
                                        P_BODY         => SUBSTR(SQLERRM, 1, 250));
Why are you programming for failure to succeed, willing to accept time taking rollbacks, committing afterward, fooling with transactions, swallowing/hiding all errors, all that 'nice and safely hidden' in the notorious WHEN OTHERS exception NOT followed by a RAISE?
Only catch errors you expect.
Programming to let a program fail is to fail.