首先我们来看下 alertSID.log 日志：
Mon Nov 30 17:31:54 2009
Thread 1 advanced to log sequence 14214 (LGWR switch)
Current log# 3 seq# 14214 mem# 0: /u03/oradata/newccs/redo03.log
Mon Nov 30 17:34:29 2009
Thread 1 advanced to log sequence 14215 (LGWR switch)
Current log# 1 seq# 14215 mem# 0: /u03/oradata/newccs/redo01.log
Mon Nov 30 17:35:54 2009
Thread 1 cannot allocate new log, sequence 14216
Checkpoint not complete
Current log# 1 seq# 14215 mem# 0: /u03/oradata/newccs/redo01.log
Mon Nov 30 17:35:55 2009
Thread 1 advanced to log sequence 14216 (LGWR switch)
Current log# 2 seq# 14216 mem# 0: /u03/oradata/newccs/redo02.log
Mon Nov 30 17:40:25 2009
Thread 1 advanced to log sequence 14217 (LGWR switch)
Current log# 3 seq# 14217 mem# 0: /u03/oradata/newccs/redo03.log
Mon Nov 30 17:44:22 2009
Thread 1 advanced to log sequence 14218 (LGWR switch)
Current log# 1 seq# 14218 mem# 0: /u03/oradata/newccs/redo01.log
我们先来分析下它的原因和后果：