2 30 4562 8 16 25 6270 ae9241
alter system flush buffer_cache;
alter system dump datafile 8 block 16;
---data block dump的结果中摘录了Rec#0x19内容：
*-----------------------------
* Rec #0x19 slt: 0x1e objn: 90344(0x000160e8) objd: 90344 tblspc: 8(0x00000008)
* Layer: 11 (Row) opc: 1 rci 0x00
Undo type: Regular undo Begin trans Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000Ext idx: 0
flg2: 0
*-----------------------------
uba: 0x02000010.187e.18 ctl max scn: 0x0000.00ae9095 prv tx scn: 0x0000.00ae909b
txn start scn: scn: 0x0000.00ae90b2 logon user: 0
prev brb: 33554460 prev bcl: 0
KDO undo record:
KTB Redo
op: 0x04 ver: 0x01
compat bit: 4 (post-11) padding: 1
op: L itl: xid: 0x0002.004.0000111f uba: 0x0200001a.177b.09
flg: C--- lkc: 0 scn: 0x0000.00ad9579
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010006f3 hdba: 0x010006f2
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 0
ncol: 3 nnew: 1 size: 2
col 0: [ 9] 58 53 24 4e 55 4c 4c 4c 4c
--将58 53 24 4e 55 4c 4c 4c 4c转换为varchar2，得到修改前的拷贝
select utl_raw.cast_to_varchar2(replace('58 53 24 4e 55 4c 4c 4c 4c',' ')) from dual;
UTL_RAW.CAST_TO_VARCHAR2(REPLACE('5853244E554C4C4C4C',''))
--------------------------------------------------------------------------------
XS$NULLLL
alter system dump undo header "_SYSSMU2$";
--下面是undo header中有关事务控制和事务表的dump内容，slot 0x1e处于活动状态，0x02000010即8/16
TRN CTL:: seq: 0x187e chd: 0x0009 ctl: 0x000e inc: 0x00000000 nfb: 0x0001
mgc: 0xb000 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x02000014.187e.13 scn: 0x0000.00ae92e6