Oracle dbms_job 在 5 秒内执行具有不同延迟的作业。 如何让它以指定的时间间隔无延迟地运行作业？

Question

I have created simple job via DBMS_JOB package (Tested under oracle 12.2 and 11.2)

begin
  sys.dbms_job.submit(job => :job,
                      what => 'null;',
                      next_date => to_date('19-06-2020 22:26:00', 'dd-mm-yyyy hh24:mi:ss'),
                      interval => 'trunc(sysdate,''MI'')+1/24/60');
  commit;
end;

It should be runned exactly every minute (no seconds delay)

Then I use

select last_date, last_sec, next_date, what,interval from all_jobs where job=:job

to monitor last start time and next start time I grabbed the output every minute and placed it to the table bellow. Here are results of job runs:

| LAST_DATE           | LAST_SEC | NEXT_DATE           | WHAT  | INTERVAL                    |
| 2020-06-19 22:33:02 | 22:33:02 | 2020-06-19 22:34:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:34:07 | 22:34:07 | 2020-06-19 22:35:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:35:13 | 22:35:13 | 2020-06-19 22:36:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:36:18 | 22:36:18 | 2020-06-19 22:37:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:37:24 | 22:37:24 | 2020-06-19 22:38:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:38:30 | 22:38:30 | 2020-06-19 22:39:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:39:05 | 22:39:05 | 2020-06-19 22:40:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:40:10 | 22:40:10 | 2020-06-19 22:41:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:41:16 | 22:41:16 | 2020-06-19 22:42:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:42:21 | 22:42:21 | 2020-06-19 22:43:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:43:27 | 22:43:27 | 2020-06-19 22:44:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:44:02 | 22:44:02 | 2020-06-19 22:45:00 | null; | trunc(sysdate,'MI')+1/24/60 |
| 2020-06-19 22:45:08 | 22:45:08 | 2020-06-19 22:46:00 | null; | trunc(sysdate,'MI')+1/24/60 |

Hmm... NEXT_DATE shows right time, but LAST_DATE / LAST_SEC shows time with delay. The delay of start job time is constantly growing from zero to 30 seconds: 2, 7, 13, 18, 24, 30. Then again from zero: 5, 10, 16, 21, 27 Then again 2, 8, ... etc.

Why does it starts every time not exactly at:00 sec and is constantly growing? How to make start it exactly at desired time?

Generally, I cannot use DBMS_SCHEDULER with calendar syntax. I need to calculate the next job time exactly with pl/sql function according to my complex algorithm.

Addition: The same delay in starting a job can be seen if you set what parameter to something like:

insert into my_table(last_date) values(sysdate);

Answer 1

DBMS_JOB has always been subject to scheduling creep, because the interval is calculated from when the job ends , so the interval is what you specify plus the time it took to run the previous job execution . If you need scheduling that precise, then you need to be using Oracle Scheduler (DBMS_SCHEDULER). It will allow you to schedule executions to the second, with no creep. Here are some resources to help you get better acquainted with it:

• https://oracle-base.com/articles/10g/scheduler-10g
• What is "INTERVAL=0" means in Oracle Schedular?
• http://www.dba-oracle.com/t_dbms_scheduler_examples.htm
• https://docs.oracle.com/database/121/ARPLS/d_sched.htm

Below is an example of DDL to create a job that runs once per minute:

BEGIN
  -- Job defined entirely by the CREATE JOB procedure.
  DBMS_SCHEDULER.create_job (
    job_name        => 'test_full_job_definition',
    job_type        => 'PLSQL_BLOCK',
    job_action      => 'BEGIN DBMS_STATS.gather_schema_stats(''SCOTT''); END;',
    start_date      => SYSTIMESTAMP,
    repeat_interval => 'freq=minutely; bysecond=0',
    end_date        => NULL,
    enabled         => TRUE,
    comments        => 'Job defined entirely by the CREATE JOB procedure.');
END;
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