摘要: 本文通过一次Oracle Job任务异常案例诊断，分析其原因及解决过程，从内部揭示Oracle Job任务调度及内部计时机制。
问题及环境
接到研发人员报告，数据库定时任务未正常执行，导致某些操作失败,开始介入处理该事故。
系统环境:
SunOS DB 5.8 Generic_108528-21 sun4u sparc SUNW,Ultra-4
Oracle9i Enterprise Edition Release 9.2.0.3.0 - ProdUCtion
解决过程
首先介入检查数据库任务
$ sqlplus "/ as sysdba"
SQL*Plus: Release 9.2.0.3.0 - Production on Wed Nov 17 20:23:53 2004
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.3.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.3.0 - Production
SQL> select job,last_date,last_sec,next_date,next_sec,broken,failures from
dba_jobs;
JOB LAST_DATE LAST_SEC NEXT_DATE NEXT_SEC B FAILURES
INTERVAL
31 16-NOV-04 01:00:02 17-NOV-04 01:00:00 N 0
trunc(sysdate+1)+1/24
27 16-NOV-04 00:00:04 17-NOV-04 00:00:00 N 0
TRUNC(SYSDATE) + 1
35 16-NOV-04 01:00:02 17-NOV-04 01:00:00 N 0
trunc(sysdate+1)+1/24
29 16-NOV-04 00:00:04 17-NOV-04 00:00:00 N 0
TRUNC(SYSDATE) + 1
30 01-NOV-04 06:00:01 01-DEC-04 06:00:00 N 0
trunc(add_months(sysdate,1),’MM’)+6/24
65 16-NOV-04 04:00:03 17-NOV-04 04:00:00 N 0
trunc(sysdate+1)+4/24
46 16-NOV-04 02:14:27 17-NOV-04 02:14:27 N 0
sysdate+1
66 16-NOV-04 03:00:02 17-NOV-04 18:14:49 N 0
trunc(sysdate+1)+3/24
8 rows selected.
发现JOB任务是都没有正常执行，最早一个应该在17-NOV-04 01:00:00执行。但是没有执行。
建立测试JOB
create or replace PROCEDURE pining
IS
BEGIN
NULL;
END;
/
variable jobno number;
variable instno number;
begin
select instance_number into :instno from v$instance;
dbms_job.submit(:jobno, ’pining;’, trunc(sysdate+1/288,’MI’),
’trunc(SYSDATE+1/288,’’MI’’)’, TRUE, :instno);
end;
/
发现同样的，不执行。但是通过dbms_job.run()执行没有任何问题。
进行恢复尝试
怀疑是CJQ0进程失效，首先设置JOB_QUEUE_PROCESSES为0，Oracle会杀掉CJQ0及相应job进程
SQL> ALTER SYSTEM SET JOB_QUEUE_PROCESSES = 0;
等2~3分钟，重新设置
SQL> ALTER SYSTEM SET JOB_QUEUE_PROCESSES = 5;
此时PMON会重起CJQ0进程
Thu Nov 18 11:59:50 2004
ALTER SYSTEM SET job_queue_processes=0 SCOPE=MEMORY;
Thu Nov 18 12:01:30 2004
ALTER SYSTEM SET job_queue_processes=10 SCOPE=MEMORY;
Thu Nov 18 12:01:30 2004
Restarting dead background process CJQ0
CJQ0 started with pid=8
但是Job仍然不执行，而且在再次修改的时候，CJQ0直接死掉了。
Thu Nov 18 13:52:05 2004
ALTER SYSTEM SET job_queue_processes=0 SCOPE=MEMORY;
Thu Nov 18 14:09:30 2004
ALTER SYSTEM SET job_queue_processes=10 SCOPE=MEMORY;
Thu Nov 18 14:10:27 2004
ALTER SYSTEM SET job_queue_processes=0 SCOPE=MEMORY;
Thu Nov 18 14:10:42 2004
ALTER SYSTEM SET job_queue_processes=10 SCOPE=MEMORY;
Thu Nov 18 14:31:07 2004
ALTER SYSTEM SET job_queue_processes=0 SCOPE=MEMORY;
Thu Nov 18 14:40:14 2004
ALTER SYSTEM SET job_queue_processes=10 SCOPE=MEMORY;
Thu Nov 18 14:40:28 2004
ALTER SYSTEM SET job_queue_processes=0 SCOPE=MEMORY;
Thu Nov 18 14:40:33 2004
ALTER SYSTEM SET job_queue_processes=1 SCOPE=MEMORY;
Thu Nov 18 14:40:40 2004
ALTER SYSTEM SET job_queue_processes=10 SCOPE=MEMORY;
Thu Nov 18 15:00:42 2004
ALTER SYSTEM SET job_queue_processes=0 SCOPE=MEMORY;
Thu Nov 18 15:01:36 2004
ALTER SYSTEM SET job_queue_processes=15 SCOPE=MEMORY;
尝试重起数据库，这个必须在晚上进行：
PMON started with pid=2
DBW0 started with pid=3
LGWR started with pid=4
CKPT started with pid=5
SMON started with pid=6
RECO started with pid=7
CJQ0 started with pid=8
QMN0 started with pid=9
....
CJQ0正常启动，但是Job仍然不执行。 没办法了...
继续研究...居然发现Oralce有这样一个bug ：
1. Clear description of the problem encountered:
slgcsf() / slgcs() on Solaris will stop incrementing after
497 days 2 hrs 28 mins (approx) machine uptime.
2. Pertinent configuration information
No special configuration other than long machine uptime. .
3. Indication of the frequency and predictability of the problem
100% but only after 497 days.
4. Sequence of events leading to the problem
If the gethrtime() OS call returns a value > 42949672950000000
nanoseconds then slgcs() stays at 0xffffffff. This can
cause some problems in parts of the code which rely on
slgcs() to keep moving.
eg: In kkjssrh() does "now = slgcs(&se)" and compares that
to a previous timestamp. After 497 days uptime slgcs()
keeps returning 0xffffffff so "now - kkjlsrt" will
always return 0. .
5. Technical impact on the customer. Include persistent after effects.
In this case DBMS JOBS stopped running after 497 days uptime.
Other symptoms could occur in various places in the code.
好么，原来是计时器溢出了，一检查我的主机:
bash-2.03$ uptime
10:00pm up 500 day(s), 14:57, 1 user, load average: 1.31, 1.09, 1.08
bash-2.03$ date
Fri Nov 19 22:00:14 CST 2004
刚好到事发时是497天多一点。安排重起主机系统，这个问题够郁闷的，谁曾想Oracle这都成...
Oracle最后声称: fix made it into 9.2.0.6 patchset。在Solaris上的9206尚未发布...晕.好了，就当是个经历吧，假如有问题非常不可思议的话，那么大胆怀疑Oracle吧，是Bug，可能就是Bug。
重起以后问题解决，状态如下:
$ sqlplus "/ as sysdba"
SQL*Plus: Release 9.2.0.3.0 - Production on Fri Nov 26 09:21:21 2004
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.3.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.3.0 - Production
SQL> select job,last_date,last_sec,next_date,next_sec from user_jobs;
JOB LAST_DATE LAST_SEC NEXT_DATE NEXT_SEC
70 26-NOV-04 09:21:04 26-NOV-04 09:26:00
SQL> /
JOB LAST_DATE LAST_SEC NEXT_DATE NEXT_SEC
70 26-NOV-04 09:26:01 26-NOV-04 09:31:00
SQL>
SQL> select * from v$timer;
HSECS
3388153
SQL> select * from v$timer;
HSECS
3388319
SQL>
FAQ
