昨天在看controlfile的dump时，发现有如下记录：
THREAD #1  ~~~ THREAD #32
LOG FILE #1~~~LOG FILE #192
UNNAMED_INSTANCE_32 recno=32
版本是10.2.0.1，一个数据库最多可以被32个instance打开，192个日志组。

***************************************************************************
CHECKPOINT PROGRESS RECORDS
***************************************************************************
 (size = 8180, compat size = 8180, section max = 35, section in-use = 0,
  last-recid= 0, old-recno = 0, last-recno = 0)
 (extent = 1, blkno = 2, numrecs = 35)
THREAD #1 - status:0x2 flags:0x0 dirty:46
low cache rba:(0x17.3.0) on disk rba:(0x17.62.0)
on disk scn: 0x0000.00107373 05/02/2011 08:38:49
resetlogs scn: 0x0000.000ef869 03/14/2011 22:49:29
heartbeat: 750117435 mount id: 747678899
THREAD #2 - status:0x0 flags:0x0 dirty:0
low cache rba:(0x0.0.0) on disk rba:(0x0.0.0)
on disk scn: 0x0000.00000000 01/01/1988 00:00:00
resetlogs scn: 0x0000.00000000 01/01/1988 00:00:00
heartbeat: 733686547 mount id: 731337548
.................................
THREAD #31 - status:0x0 flags:0x0 dirty:0
low cache rba:(0x0.0.0) on disk rba:(0x0.0.0)
on disk scn: 0x0000.00000000 01/01/1988 00:00:00
resetlogs scn: 0x0000.00000000 01/01/1988 00:00:00
heartbeat: 0 mount id: 0
THREAD #32 - status:0x0 flags:0x0 dirty:0
low cache rba:(0x0.0.0) on disk rba:(0x0.0.0)
on disk scn: 0x0000.00000000 01/01/1988 00:00:00
resetlogs scn: 0x0000.00000000 01/01/1988 00:00:00
heartbeat: 0 mount id: 0

***************************************************************************
LOG FILE RECORDS
***************************************************************************
 (size = 72, compat size = 72, section max = 192, section in-use = 192,
  last-recid= 90, old-recno = 0, last-recno = 0)
 (extent = 1, blkno = 22, numrecs = 192)
LOG FILE #1:
  (name #1) /data/ora10g/RACDBSTD/group_1.257.727735489
 Thread 1 redo log links: forward: 2 backward: 0
 siz: 0x19000 seq: 0x00000017 hws: 0x2 bsz: 512 nab: 0xffffffff flg: 0xa dup: 1
 Archive links: fwrd: 0 back: 0 Prev scn: 0x0000.0010721f
 Low scn: 0x0000.0010731b 05/02/2011 08:38:35
 Next scn: 0xffff.ffffffff 01/01/1988 00:00:00
LOG FILE #2:
  (name #2) /data/ora10g/RACDBSTD/group_2.258.727735493
 Thread 1 redo log links: forward: 0 backward: 1
 siz: 0x19000 seq: 0x00000016 hws: 0x5 bsz: 512 nab: 0x249 flg: 0x1 dup: 1
 Archive links: fwrd: 0 back: 0 Prev scn: 0x0000.000ffda7
 Low scn: 0x0000.0010721f 05/02/2011 08:27:11
 Next scn: 0x0000.0010731b 05/02/2011 08:38:35
.................................
LOG FILE #191:
 Thread 0 redo log links: forward: 0 backward: 0
 siz: 0x0 seq: 0x00000000 hws: 0x0 bsz: 0 nab: 0x0 flg: 0x3 dup: 0
 Archive links: fwrd: 0 back: 0 Prev scn: 0x0000.00000000
 Low scn: 0x0000.00000000 01/01/1988 00:00:00
 Next scn: 0x0000.00000000 01/01/1988 00:00:00
LOG FILE #192:
 Thread 0 redo log links: forward: 0 backward: 0
 siz: 0x0 seq: 0x00000000 hws: 0x0 bsz: 0 nab: 0x0 flg: 0x3 dup: 0
 Archive links: fwrd: 0 back: 0 Prev scn: 0x0000.00000000
 Low scn: 0x0000.00000000 01/01/1988 00:00:00
 Next scn: 0x0000.00000000 01/01/1988 00:00:00

***************************************************************************
THREAD INSTANCE MAPPING RECORDS
***************************************************************************
 (size = 80, compat size = 80, section max = 32, section in-use = 32,
  last-recid= 0, old-recno = 0, last-recno = 0)
 (extent = 1, blkno = 407, numrecs = 32)
RACDBSTD recno=1
RACDB2 recno=2
UNNAMED_INSTANCE_3 recno=3
UNNAMED_INSTANCE_4 recno=4
UNNAMED_INSTANCE_5 recno=5
UNNAMED_INSTANCE_6 recno=6
UNNAMED_INSTANCE_7 recno=7
UNNAMED_INSTANCE_8 recno=8
UNNAMED_INSTANCE_9 recno=9
UNNAMED_INSTANCE_10 recno=10
UNNAMED_INSTANCE_11 recno=11
UNNAMED_INSTANCE_12 recno=12
UNNAMED_INSTANCE_13 recno=13
UNNAMED_INSTANCE_14 recno=14
UNNAMED_INSTANCE_15 recno=15
UNNAMED_INSTANCE_16 recno=16
UNNAMED_INSTANCE_17 recno=17
UNNAMED_INSTANCE_18 recno=18
UNNAMED_INSTANCE_19 recno=19
UNNAMED_INSTANCE_20 recno=20
UNNAMED_INSTANCE_21 recno=21
UNNAMED_INSTANCE_22 recno=22
UNNAMED_INSTANCE_23 recno=23
UNNAMED_INSTANCE_24 recno=24
UNNAMED_INSTANCE_25 recno=25
UNNAMED_INSTANCE_26 recno=26
UNNAMED_INSTANCE_27 recno=27
UNNAMED_INSTANCE_28 recno=28
UNNAMED_INSTANCE_29 recno=29
UNNAMED_INSTANCE_30 recno=30
UNNAMED_INSTANCE_31 recno=31
UNNAMED_INSTANCE_32 recno=32