Database job execution time changing

Question

Hello,
I created a job to execute every 15 minutes. What I have noticed is it is not getting executed every 15 minutes, instead period is increasing over 1 or 2 minutes.
Here is my code for job, is it because of seconds it is making the difference?
DECLARE
X NUMBER;
BEGIN
SYS.DBMS_JOB.SUBMIT
( job => X
,what => 'myproc'
,next_date => to_date('20/08/2006 07:34:10','dd/mm/yyyy hh24:mi:ss')
,interval => 'sysdate+30/2750'
,no_parse => TRUE
END;
/

Answer 1

You need to use date functions that evaluate to a FIXED time in the future (see AskTom for further explanation: http://asktom.oracle.com/pls/ask/f?p=4950:8:9447876042389067866::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:13317229864022)
The preferred method would be to create custom-built function that returns the required interval. The function can use hard-coded logic (like the example below) or it can read from simple "repository" (set of tables with job schedules, maintenance windows etc.).
Example:
1) Create next_date function
CREATE OR REPLACE FUNCTION next_date
RETURN DATE IS
v_date_portion_1 VARCHAR2(16);
v_date_portion_2 PLS_INTEGER;
v_date_portion_3 PLS_INTEGER;
v_next_date DATE;
BEGIN
v_date_portion_1 := TO_CHAR(sysdate, 'dd.mm.yyyy');
v_date_portion_2 := TO_CHAR(sysdate, 'hh24');
v_date_portion_3 := TO_NUMBER(TO_CHAR(sysdate, 'mi'));
v_next_date:= TO_DATE(v_date_portion_1||' '||
(CASE
WHEN v_date_portion_3 < 15 THEN TO_CHAR(v_date_portion_2)||':'||'15'
WHEN v_date_portion_3 >= 15 AND
v_date_portion_3 < 30 THEN TO_CHAR(v_date_portion_2)||':'||'30'
WHEN v_date_portion_3 >= 30 AND
v_date_portion_3 < 45 THEN TO_CHAR(v_date_portion_2)||':'||'45'
ELSE TO_CHAR(v_date_portion_2 + 1)||':'||'00'
END), 'dd.mm.yyyy hh24:mi');
RETURN v_next_date;
END next_date;
2) Change interval
BEGIN
DBMS_JOB.CHANGE(<your_job>,
null,
     null,
     interval=>'next_date');
END;