DBMS_JOB으로 만들어진 JOB의 interval을 1초로 지정해도 5초 정도의 interval을 갖는다?

네이버 지식인에 DBMS_JOB으로 만들어진 JOB의 interval을 1초로 지정해도 

5초 정도의 interval을 갖는다는 질문이 있어 간단히 테스트 해 봤습니다. 

DBMS_JOB package로 job을 생성합니다 

SQL> variable jobno number;

SQL> begin

SQL> dbms_job.submit(:jobno,'insert into test values (sysdate);',

SQL> sysdate,'sysdate+1/60/24/50',FALSE);

SQL> end;

SQL> /

PL/SQL procedure successfully completed.

SQL> print jobno

     JOBNO

----------

        21

SQL> exec dbms_job.run(21);

PL/SQL procedure successfully completed.

SQL> commit;

Commit complete.

SQL> select * from user_jobs;

       JOB LOG_USER                       PRIV_USER                      SCHEMA_USER                    LAST_DATE LAST_SEC         THIS_DATE THIS_SEC         NEXT_DATE NEXT_SEC         TOTAL_TIME B

---------- ------------------------------ ------------------------------ ------------------------------ --------- ---------------- --------- ---------------- --------- ---------------- ---------- -

INTERVAL

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

  FAILURES

----------

WHAT

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

NLS_ENV

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

MISC_ENV                                                           INSTANCE

---------------------------------------------------------------- ----------

        21 SYS                            SYS                            SYS                            12-OCT-10 16:50:28                                    12-OCT-10 16:50:29                  0 N

sysdate+1/60/24/50

         0

insert into test values (sysdate);

NLS_LANGUAGE='AMERICAN' NLS_TERRITORY='AMERICA' NLS_CURRENCY='$' NLS_ISO_CURRENCY='AMERICA' NLS_NUMERIC_CHARACTERS='.,' NLS_DATE_FORMAT='DD-MON-RR' NLS_DATE_LANGUAGE='AMERICAN' NLS_SORT='BINARY'

0102000202000000                                                          0

JOB 내역을 보면 정상적으로 NEXT_DATE는 LAST_DATE + 1초로 나옵니다 

SQL> alter session set nls_date_format = 'YYYY/MM/DD HH24:MI:SS';

Session altered.

SQL> select * from test;

COMMIT_DATE

-------------------

2010/10/12 16:50:04

2010/10/12 16:50:08

2010/10/12 16:50:13

2010/10/12 16:50:18

2010/10/12 16:50:23

2010/10/12 16:50:28

2010/10/12 16:50:33

2010/10/12 16:50:38

2010/10/12 16:50:43

2010/10/12 16:50:48

2010/10/12 16:50:53

2010/10/12 16:50:58

2010/10/12 16:51:03

2010/10/12 16:51:08

14 rows selected.

그러나 table에 들어간 시간을 보니 4초 차이가 발생하는 군요...

SQL> exec dbms_job.broken(21,TRUE);

PL/SQL procedure successfully completed.

SQL> exec dbms_job.remove(21);

PL/SQL procedure successfully completed.

SQL> delete from test;

25 rows deleted.

SQL> commit;

Commit complete.

이번엔 DBMS_SCHEDULER로 테스트 해봤습니다. 

SQL> begin

  2  dbms_scheduler.create_schedule(

schedule_name  => 'INTERVAL_EVERY_1_SECONDS',

  start_date    => trunc(sysdate),

  repeat_interval => 'freq=SECONDLY;interval=1',

  comments     => 'Runtime: Every day all 1 SECONDS');  3    4    5    6  

  7  end;

  8  /

PL/SQL procedure successfully completed.

1초에 한번씩 수행할 Schedule을 생성합니다 

SQL> begin

dbms_scheduler.create_program

(program_name=> 'TEST_PROC01',

 program_type=> 'STORED_PROCEDURE',

 program_action=> 'SYS.TEST_PROC',

 enabled=>true,

 comments=>'job interval test'

 );

end;

/ 

PL/SQL procedure successfully completed.

수행할 Program을 생성합니다. 

TEST_PROC는 test table에 sysdate를 입력하는 procedure 입니다.

SQL> begin

dbms_scheduler.create_job

 (job_name => 'JOB_TEST',

  program_name=> 'TEST_PROC01',

  schedule_name=>'INTERVAL_EVERY_1_SECONDS',

  enabled=>true,

  auto_drop=>false,

  comments=>'job test');

end;

/  

PL/SQL procedure successfully completed.

이제 먼저 생성한 schedule과 program을 이용해 JOB을 생성합니다 

SQL> begin

dbms_scheduler.run_job('JOB_TEST',TRUE);

end; 

/

PL/SQL procedure successfully completed.

SQL> select * from test;

COMMIT_DATE

-------------------

2010/10/12 17:12:38

2010/10/12 17:12:39

2010/10/12 17:12:40

2010/10/12 17:12:41

2010/10/12 17:12:42

2010/10/12 17:12:43

2010/10/12 17:12:44

2010/10/12 17:12:45

2010/10/12 17:12:46

2010/10/12 17:12:47

2010/10/12 17:12:48

2010/10/12 17:12:49

2010/10/12 17:12:50

2010/10/12 17:12:51

2010/10/12 17:12:52

2010/10/12 17:12:53

2010/10/12 17:12:54

2010/10/12 17:12:55

2010/10/12 17:12:55

2010/10/12 17:12:56

2010/10/12 17:12:57

2010/10/12 17:12:58

2010/10/12 17:12:59

2010/10/12 17:13:00

2010/10/12 17:13:01

...

table에 들어간 데이터를 보니 1초에 한번씩 수행하고 있군요.. 

DBMS_JOB을 이용한 job은 interval에 제한이 있는 걸까요? 그런 자료는 못 본것 같은데..

예전 oracle 8에서 job_queue_interval parameter가 있을때

수행 시간이 job_queue_interval 주기때문에 job interval이 정확히 계산되지 않았던 것 같은데... 

혹시 job_queue_process가 wake-up 하는 시간때문일까요?