RMAN> run{
      debug on;
      set until time "to_date('2013-08-08 19:12:03','yyyy-mm-dd hh24:mi:ss')";
      restore database ;
      debug off;
}
2> 3> 4> 5> 6>
RMAN-03036: Debugging set to level=9, types=ALL

RMAN-03023: executing command: SET until clause

RMAN-03090: Starting restore at 2013-08-15 10:19:14
RMAN-06009: using target database control file instead of recovery catalog
RMAN-08030: allocated channel: ORA_DISK_1
RMAN-08605: channel ORA_DISK_1: SID=661 instance=PTRDDB1 device type=DISK

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 08/15/2013 10:19:18
RMAN-06026: some targets not found - aborting restore
RMAN-06100: no channel to restore a backup or copy of datafile 7
RMAN-06100: no channel to restore a backup or copy of datafile 4
RMAN-06100: no channel to restore a backup or copy of datafile 3
RMAN-06100: no channel to restore a backup or copy of datafile 2
RMAN-06100: no channel to restore a backup or copy of datafile 1

RMAN>

RMAN>

RMAN>

RMAN>

RMAN>

RMAN> run{
      debug on;
      set until time "to_date('2013-08-08 19:12:03','yyyy-mm-dd hh24:mi:ss')";
      restore database preview;
      debug off;
}2> 3> 4> 5> 6>

RMAN-03036: Debugging set to level=9, types=ALL

RMAN-03023: executing command: SET until clause

RMAN-03090: Starting restore at 2013-08-15 10:19:48
RMAN-12016: using channel ORA_DISK_1

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 08/15/2013 10:19:54
RMAN-06026: some targets not found - aborting restore
RMAN-06100: no channel to restore a backup or copy of datafile 7
RMAN-06100: no channel to restore a backup or copy of datafile 4
RMAN-06100: no channel to restore a backup or copy of datafile 3
RMAN-06100: no channel to restore a backup or copy of datafile 2
RMAN-06100: no channel to restore a backup or copy of datafile 1

recid file# checkpoint_time checkpoint_change# ABSOLUTE_FUZZY_CHANGE#
3934 3 2013-08-08 19:00:50 424443795 424454469
3935 4 2013-08-08 19:00:50 424443795 424454521
3936 7 2013-08-08 19:00:50 424443795 424456295
3937 8 2013-08-08 19:00:50 424443795 0
3938 9 2013-08-08 19:00:50 424443795 0
3939 2 2013-08-08 19:00:50 424443795 424452449
3940 5 2013-08-08 19:00:50 424443795 0
3941 1 2013-08-08 19:00:50 424443795 424453386
3942 10 2013-08-08 19:00:50 424443795 0
3943 6 2013-08-08 19:00:50 424443795 0
3944 11 2013-08-08 19:00:50 424443795 0
3945 0 2013-08-08 19:00:50 424443795 0
3946 0 2013-08-08 19:00:50 424443795 0
3948 0 2013-08-08 19:00:50 424443795 0
3949 0 2013-08-08 19:27:03 424492130 0

ABSOLUTE_FUZZY_CHANGE#是rman备份中服务进程读取到数据块中的High Scn，为了维护一致性要求 restore时恢复到的时间点 要 大约备份点对应的checkpoint_change#和ABSOLUTE_FUZZY_CHANGE#。

Backup start on T1 (SCN=1000) and ends on T2 (SCN=1050), than the backup can ONLY be used if the UNTIL SCN is 1050 or higher.
So if the ‘UNTIL TIME T2′ is converted to SCN 1045, than this backup will NOT be used.
V$BACKUP_DATAFILE / RC_BACKUP_DATAFILE is giving more info on this.
CHECKPOINT_CHANGE# corresponds with T1
ABSOLUTE_FUZZY_CHANGE# corresponds with T2. When ABSOLUTE_FUZZY_CHANGE# is NULL, than it is the same as the CHECKPOINT_CHANGE#

RMAN> run
{
      set until scn 424456295;
      restore database preview;
}2> 3> 4> 5>

executing command: SET until clause

Starting restore at 2013-08-15 13:30:39
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=649 instance=PTRDDB1 device type=DISK

List of Backup Sets
===================

BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ -------------------
6719 Full 554.91M DISK 00:02:38 2013-08-08 19:07:21
BP Key: 6719 Status: AVAILABLE Compressed: YES Tag: TAG20130808T190511
Piece Name: /export/home/oracle/rman/ptddb_before_3nogq6j8
List of Datafiles in backup set 6719
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- ------------------- ----

scn 424456290 194CB062 194cb062 08/08/2013 19:07:00
scn 424464586 194CD0CA 194cd0ca 08/08/2013 19:12:03
scn 424456295 194CB067 194cb067 08/08/2013 19:07:00 ==>之前使用成功的SCN号对应的时间点

RMAN> run{
      set until time "to_date('2013-08-08 19:07:20','yyyy-mm-dd hh24:mi:ss')";
      restore database preview;
}2> 3> 4>

executing command: SET until clause

Starting restore at 2013-08-15 13:28:41
using channel ORA_DISK_1

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 08/15/2013 13:28:42
RMAN-06026: some targets not found - aborting restore
RMAN-06100: no channel to restore a backup or copy of datafile 7
RMAN-06100: no channel to restore a backup or copy of datafile 4
RMAN-06100: no channel to restore a backup or copy of datafile 3
RMAN-06100: no channel to restore a backup or copy of datafile 2
RMAN-06100: no channel to restore a backup or copy of datafile 1

When an SET UNTIL TIME is being used, RMAN will convert it to an UNTIL SCN. This is an estimate as there is NO hard relation between a timestamp and an SCN.
RMAN is making an estimate. Especially when a timestamp is used which is close to the end-time of the backup, than this might be an issue. If the conversion to an SCN is generating an SCN which is BEFORE the end fuzziness of the datafiles in the backup, than the backup can NOT be used.

ABSOLUTE_FUZZY_CHANGE#信息可以通过V$BACKUP_DATAFILE视图获得。

--转自