通过dump datafile header 发现每个Checkpoint cnt不同

大致原因如下：

1.tablespace 建立的时间不同 现在我们新建一个tablespace ->liu datafile->liu01.dbf

DATA FILE #10:
(name #14) /u01/liu01.dbf
creation size=128 block size=8192 status=0xe head=14 tail=14 dup=1
tablespace 8, index=8 krfil=10 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:2 scn: 0x0000.005339bb 10/24/2011 10:19:42
Stop scn: 0xffff.ffffffff 10/24/2011 10:19:42
Creation Checkpointed at scn: 0x0000.005339ba 10/24/2011 10:19:42
thread:1 rba:(0x37.c3a3.10)

DATA FILE #1:
(name #7) /u01/app/oracle/oradata/css/system01.dbf
creation size=0 block size=8192 status=0xe head=7 tail=7 dup=1
tablespace 0, index=1 krfil=1 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:131 scn: 0x0000.0052d2cc 10/22/2011 09:58:13
Stop scn: 0xffff.ffffffff 10/21/2011 17:10:54

2.当tablespace 处于hot backup 或者offline 的时候 发生checkpoint 我们再建一个tablespace ->liu01 datafile ->liu101.dbf

DATA FILE #11:
(name #15) /u01/liu101.dbf
creation size=128 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 9, index=9 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:2 scn: 0x0000.00533ffe 10/24/2011 10:25:22

alter tablespace liu begin backup;

DATA FILE #10:
(name #14) /u01/liu01.dbf
creation size=128 block size=8192 status=0xe head=14 tail=14 dup=1
tablespace 8, index=8 krfil=10 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:8 scn: 0x0000.00534033 10/24/2011 10:26:56

DATA FILE #11:
(name #15) /u01/liu101.dbf
creation size=128 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 9, index=9 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:7 scn: 0x0000.0053426f 10/24/2011 10:40:00

alter tablespace liu end backup;

DATA FILE #10:
(name #14) /u01/liu01.dbf
creation size=128 block size=8192 status=0xe head=14 tail=14 dup=1
tablespace 8, index=8 krfil=10 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:10 scn: 0x0000.005342b8 10/24/2011 10:43:15

DATA FILE #11:
(name #15) /u01/liu101.dbf
creation size=128 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 9, index=9 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:8 scn: 0x0000.005342b8 10/24/2011 10:43:15

alter tablespace liu offline;

DATA FILE #10:
(name #14) /u01/liu01.dbf
creation size=128 block size=8192 status=0x80 head=14 tail=14 dup=1
tablespace 8, index=8 krfil=10 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:11 scn: 0x0000.005342e7 10/24/2011 10:45:15

DATA FILE #11:
(name #15) /u01/liu101.dbf
creation size=128 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 9, index=9 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:9 scn: 0x0000.005342fd 10/24/2011 10:45:23

可以设置事件查看chk cnt

alter session set events = ‘immediate trace name file_hdrs level 10’