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 3126.1366562 (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: 0984080

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: 0984080

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 3126.1366562 (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: 0984080

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: 0984080

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

……