update一条语句的来龙去脉(三)

0x1f 10 0x80 0x10bc 0x0013 0x0000.0050c823 0x024092df 0x0000.000.00000000 0x00000001 0x00000000 0

UNDO BLK:

xid: 0x0014.01f.000010bc seq: 0x5b cnt: 0x1 irb: 0x1 icl: 0x0 flg: 0x0000

Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset

---------------------------------------------------------------------------

0x01 0x1f48

################################################################

总结：这是第一步：首先要在undo空间中分配事务槽等信息：

CHANGE #2 TYP:1 CLS:56 AFN:9 DBA:0x024092df OBJ:4294967295 SCN:0x0000.0050c823 SEQ:1 OP:5.1 ENC:0 RBL:0

ktudb redo: siz: 160 spc: 0 flg: 0x000a seq: 0x005b rec: 0x01

xid: 0x0014.01f.000010bc

ktubl redo: slt: 31 rci: 0 opc: 11.1 [objn: 89179 objd: 89716 tsn: 8]

Undo type: Regular undo Begin trans Last buffer split: No

Temp Object: No

Tablespace Undo: No

0x00000000 prev ctl uba: 0x024092de.005b.25

prev ctl max cmt scn: 0x0000.005072ce prev tx cmt scn: 0x0000.0050730f

txn start scn: 0xffff.ffffffff logon user: 92 prev brb: 37786328 prev bcl: 0 BuExt idx: 0 flg2: 0

KDO undo record:

KTB Redo

op: 0x03 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: Z

KDO Op code: URP row dependencies Disabled

xtype: XA flags: 0x00000000 bdba: 0x01c0296e hdba: 0x01c0296a

itli: 2 ispac: 0 maxfr: 4858

tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 0

ncol: 8 nnew: 1 size: -1

col 1: [ 3] 41 4d 59

从第二个向量中可以获得的信息有：相对文件号为：9，数据的前镜像地址为dba:数据文件号为9，数据块为：37599，redo的操作码：op：5.1（Opcode 1 : Undo block or undo segment header - KTURDB），可以看到这里的事务号：xid: 0x0014.01f.000010bc获得回滚段为20事务槽位31wrap为10bc，后边记录的： slt: 31 rci: 0 opc: 11.1 [objn: 89179 objd: 89716 tsn: 8]表示：事务槽为31，rci为0说明这是在undo chain中最后一个的记录，对象变化为89179，数据对象变化为89716 tsn：为8，如下查询可知道正是我操作的这张表。另外登录的用户为rhys（通过92可知），然后在记录的就是前字段值为：41 4d 59转储为：AMY这正是原先字段值。如下是获得部分信息的查询操作：

SQL> col object_name for a50

SQL> r

1* select object_name,object_id,data_object_id,object_type from dba_objects where object_id=89179

OBJECT_NAME OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE

-------------------------------------------------- ---------- -------------- -------------------

EMP 89179 89716 TABLE

SQL> select * from v$tablespace;

TS# NAME INC BIG FLA ENC

---------- ------------------------------ --- --- --- ---

0 SYSTEM YES NO YES

1 SYSAUX YES NO YES

4 USERS YES NO YES

3 TEMP NO NO YES

6 EXAMPLE YES NO YES

7 STATSPACK YES NO YES

8 RHYS YES NO YES

9 INDEX_TABLESPACE YES NO YES

10 UNDOTBS02 YES NO YES

9 rows selected.

SQL> select username,user_id from dba_users where user_id=92;

USERNAME USER_ID

------------------------------ ----------

RHYS 92

SQL>

SQL> col value for a40

SQL> r

1* select utl_raw.cast_to_varchar2(replace('41 4d 59',' ')) value from dual

VALUE

----------------------------------------

AMY

SQL>

这是第三个改变向量。

CHANGE #3 TYP:2 CLS:1 AFN:7 DBA:0x01c0296e OBJ:89716 SCN:0x0000.00505633 SEQ:1 OP:11.5 ENC:0 RBL:0

KTB Redo

op: 0x11 ver: 0x01

compat bit: 4