Extract进程（SEXTR01）状态为running，但是Lag at Chkpt却达到5个多小时，且时间一直在增长，根本就不抽取新日志，状态信息如下
1、故障现象
Extract进程（SEXTR01）状态为running，但是Lag at Chkpt却达到5个多小时，且时间一直在增长，根本就不抽取新日志，状态信息如下：
GGSCI (caXXadgdb) 21> info all
Program Status Group Lag at Chkpt Time Since Chkpt
MANAGER RUNNING
EXTRACT RUNNING DPEYWGL 00:00:00 00:00:04
EXTRACT RUNNING SEXTR01 05:14:58 00:00:03
2、故障分析
2.1 debug一下进程状态信息
GGSCI (caXXadgdb) 23> info sextr01, showch debug
EXTRACT SEXTR01 Last Started 2015-01-25 22:51 Status RUNNING
Checkpoint Lag 05:21:26 (updated 00:00:04 ago)
Log Read Checkpoint Oracle Redo Logs
2015-01-25 18:05:16 Thread 1, Seqno 5554, RBA 611373536
SCN 3126.136656462 (13426204423758)
Log Read Checkpoint Oracle Redo Logs
1988-01-01 00:00:00 Thread 2, Seqno 4016, RBA 1024
SCN 44527.110828288 (191242119617280)
Current Checkpoint Detail:
Read Checkpoint #1
……
Read Checkpoint #2
Oracle Threaded Redo Log
Startup Checkpoint (starting position in the data source):
Thread #: 2
Sequence #: 4015
RBA: 640984080
Timestamp: 2015-01-25 18:03:51.000000
SCN: 3126.136602577 (13426204369873)
Redo File: +DGROUP1/caXXdb/onlinelog/group_15.267.799673791
Recovery Checkpoint (position of oldest unprocessed transaction in the data source):
Thread #: 2
Sequence #: 4015
RBA: 640984080
Timestamp: 2015-01-25 18:03:51.000000
SCN: 3126.136602577 (13426204369873)
Redo File: +DGROUP1/caXXdb/onlinelog/group_15.267.799673791
Current Checkpoint (position of last record read in the data source):
Thread #: 2
Sequence #: 4016
RBA: 1024
Timestamp: 1988-01-01 00:00:00.000000
SCN: 44527.110828288 (191242119617280)
Redo File: +DGROUP1/caXXdb/onlinelog/group_16.266.799673793
……
从这里发现一个不可思议的问题：
Thread #: 2的current checkpoint 的timestamp竟然是1988-01-0100:00:00.000000，SCN的十进制数，竟然为191242119617280，远远大于当前数据库的SCN，多出一位数。
时间倒退，SCN号反而大涨，时间还那么有个性。这个问题挺有意思。
2.2 view extract进程的report
使用view report sextr01查看进程的报告，提示有ERROR，thread#2 4016 archive log 不能打开。（由于笔者没有将信息复制下来，所以当时的状态只能这么描述了），但是4016号archivelog实际物理文件是存在的，而且权限正常。
2.3 将进程停止下来，showch其状态
GGSCI (calladgdb) 24>stop sextr01
GGSCI (calladgdb) 25> info SEXTR01, showch
EXTRACT SEXTR01 Last Started 2015-01-26 01:00 Status STOPPED
Checkpoint Lag 06:56:55 (updated 00:00:58 ago)
Log Read Checkpoint Oracle Redo Logs
2015-01-25 18:05:16 Thread 1, Seqno 5554, RBA 611373536
SCN 3126.136656462 (13426204423758)
Log Read Checkpoint Oracle Redo Logs
1988-01-01 00:00:00 Thread 2, Seqno 4016, RBA 1024
SCN 44527.110828288 (191242119617280)
Current Checkpoint Detail:
Read Checkpoint #1
……
Read Checkpoint #2
Oracle Threaded Redo Log
Startup Checkpoint (starting position in the data source):
Thread #: 2
Sequence #: 4015
RBA: 640984080
Timestamp: 2015-01-25 18:03:51.000000
SCN: 3126.136602577 (13426204369873)
Redo File: +DGROUP1/caXXdb/onlinelog/group_15.267.799673791
Recovery Checkpoint (position of oldest unprocessed transaction in the data source):
Thread #: 2
Sequence #: 4015
RBA: 640984080
Timestamp: 2015-01-25 18:03:51.000000
SCN: 3126.136602577 (13426204369873)
Redo File: +DGROUP1/caXXdb/onlinelog/group_15.267.799673791
Current Checkpoint (position of last record read in the data source):
Thread #: 2
Sequence #: 4016
RBA: 1024
Timestamp: 1988-01-01 00:00:00.000000
SCN: 44527.110828288 (191242119617280)
Redo File: +DGROUP1/caXXdb/onlinelog/group_16.266.799673793
……
