這篇文章主要描寫敘述oracle的回滾機制，篇幅可能較長，由於對於oracle的回滾機制來說，要討論和描寫敘述的實在太多，僅僅能刷選自己覺得最有意義的一部分進行深入研究和分享
一、我們來看一個DML語句的處理過程描寫敘述
update undotest set object_type='VIEW' where object_type='PROCEDURE';
- 檢查shared pool中是否存在同樣的語句。假設存在。重用運行計划，運行掃描運算，假設不存在。運行硬解析生成運行計划
- 依據運行計划中的掃描運算，檢查undotest表中的相關數據塊是否存在buffer cache中，假設不存在則讀取到內存中
- 檢查數據塊中符合object_type='PROCEDURE'條件的記錄，假設沒有符合條件的行記錄，則結束語句。假設存在則進入下一步
- 以當前模式（current）獲取符合object_type='PROCEDURE'條件的數據塊，准備進行更新
- 在回滾表空間的對應回滾段頭的事務表上分配事務槽，這個動作須要記錄redo日志
- 從回滾段數據塊上創建object_type='PROCEDURE'的前映像數據，這個動作也要記錄redo日志
- 改動object_type='VIEW' ，這是DML操作的數據變更，而須要記錄redo日志
- 用戶提交時，在redo日志中記錄提交信息，將回滾段頭上的事務表和回滾段數據塊標記為非活動，清除改動數據塊上的事務信息（也可能延遲清除）。同一時候必須確保整個事務的redp日志寫到磁盤上的日志文件
注意：假設最后用戶回滾了事務，oracle從回滾段中將前映像數據提取出來，覆蓋被更新的數據塊。這個回滾動作本身也須要產生redo日志，因此。我們要知道回滾的代價很昂貴。
二、不同的DML操作，UNDO BLOCK中保存的前映像內容
- INSERT操作，UNDO中僅僅須要保存插入記錄的rowid，假設須要回退，通過保存的rowid進行刪除就可以（后面有案例）
- UPDATE操作。UNDO中僅僅須要記錄被更新字段的舊值，假設須要回退，僅僅須要通過舊值覆蓋更新后的值就可以。
- DELETE操作。UNDO中必須記錄整行的數據。假設須要回退，僅僅須要將這整行的數據又一次插入至表中就可以。
備注：本文章僅僅對INSERT操作。UNDO中保存的內容進行測試。至於UPDATE、DELETE操作。實驗方法基本一致，這里就不再累贅
演示樣例
1.開啟事務
SQL
>
create
table tt
as
select object_name,object_id
from dba_objects;
Table created.
SQL > insert into tt values( 'dddddd', 1233456); --運行insert操作
1 row created.
Table created.
SQL > insert into tt values( 'dddddd', 1233456); --運行insert操作
1 row created.
2.檢查事務信息和其它一些事務信息
SQL > select HEADER_FILE,HEADER_BLOCK from dba_segments a where segment_name = 'TT';
HEADER_FILE HEADER_BLOCK
- - - - - - - - - - - - - - - - - - - - - - -
4 810
SQL > SELECT
2 dbms_rowid.rowid_object(rowid) object_id,
3 dbms_rowid.rowid_relative_fno(rowid) REL_FNO,
4 dbms_rowid.rowid_block_number(rowid) BLOCKNO,
5 dbms_rowid.rowid_row_number(rowid) ROWNO,rowid,object_name
6 FROM tt WHERE object_name = 'dddddd';
OBJECT_ID REL_FNO BLOCKNO ROWNO ROWID
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
OBJECT_NAME
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
73430 4 1150 0 AAAR7WAAEAAAAR +AAA
dddddd
SQL > select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec,to_char(start_scnw, 'xxxxxxxx') start_scnw,
2 to_char(start_scnb, 'xxxxxxxx') start_scnb, start_scnb +start_scnw *power( 2, 32) start_scn
3 from v$ transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC START_SCNW START_SCNB START_SCN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
5 21 960 1466 3 7 0 f5520 1004832
依據上面查詢獲取的事務信息，dump insert事務undo 段頭和undo 塊
SQL > select HEADER_FILE,HEADER_BLOCK from dba_segments a where segment_name = 'TT';
HEADER_FILE HEADER_BLOCK
- - - - - - - - - - - - - - - - - - - - - - -
4 810
SQL > SELECT
2 dbms_rowid.rowid_object(rowid) object_id,
3 dbms_rowid.rowid_relative_fno(rowid) REL_FNO,
4 dbms_rowid.rowid_block_number(rowid) BLOCKNO,
5 dbms_rowid.rowid_row_number(rowid) ROWNO,rowid,object_name
6 FROM tt WHERE object_name = 'dddddd';
OBJECT_ID REL_FNO BLOCKNO ROWNO ROWID
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
OBJECT_NAME
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
73430 4 1150 0 AAAR7WAAEAAAAR +AAA
dddddd
SQL > select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec,to_char(start_scnw, 'xxxxxxxx') start_scnw,
2 to_char(start_scnb, 'xxxxxxxx') start_scnb, start_scnb +start_scnw *power( 2, 32) start_scn
3 from v$ transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC START_SCNW START_SCNB START_SCN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
5 21 960 1466 3 7 0 f5520 1004832
依據上面查詢獲取的事務信息，dump insert事務undo 段頭和undo 塊
SQL
>
select
name
from v$rollname
where usn
=
5;
NAME
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
_SYSSMU5_1527469038$
NAME
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
_SYSSMU5_1527469038$
3.dump undo 段頭和undo 塊
SQL > oradebug setmypid;
Statement processed.
SQL > oradebug tracefile_name
/u01 /oracle /diag /rdbms /test /test /trace /test_ora_604.trc
SQL > alter system dump undo header '_SYSSMU5_1527469038$';
System altered.
SQL > alter system dump datafile 3 block 1466;
System altered.
UNDO BLK:
xid: 0x0005. 015. 000003c0 seq: 0x12c cnt: 0x7 irb: 0x7 icl: 0x0 flg: 0x0000
Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x01 0x1fa4 0x02 0x1f48 0x03 0x1ecc 0x04 0x1e70 0x05 0x1df4
0x06 0x1d90 0x07 0x1d20
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x7 slt: 0x15 objn: 73430(0x00011ed6) objd: 73430 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x00
Undo type: Regular undo Begin trans Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000Ext idx: 0
flg2: 0
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
uba: 0x00c005b9. 012c. 2d ctl max scn: 0x0000.000f4ed4 prv tx scn: 0x0000.000f4ee0
txn start scn: scn: 0x0000.000f53a9 logon user: 85
prev brb: 12584373 prev bcl: 0
KDO undo record:
KTB Redo
op: 0x03 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: Z
KDO Op code: DRP row dependencies Disabled --DRP操作完畢回滾
xtype: XA flags: 0x00000000 bdba: 0x0100047e hdba: 0x0100032a --bdba表示block address hdba 代表sgment header address
itli: 1 ispac: 0 maxfr: 4858
tabn: 0 slot: 0(0x0) - - - - - - - - - 這個slot表示這一行數據在數據塊中的行地址（行序列）
當中bdba表示file 4，block 1150 ,hdba表示file 4。block 810 與我們上面查詢出來的地址相符。
SQL > oradebug setmypid;
Statement processed.
SQL > oradebug tracefile_name
/u01 /oracle /diag /rdbms /test /test /trace /test_ora_604.trc
SQL > alter system dump undo header '_SYSSMU5_1527469038$';
System altered.
SQL > alter system dump datafile 3 block 1466;
System altered.
UNDO BLK:
xid: 0x0005. 015. 000003c0 seq: 0x12c cnt: 0x7 irb: 0x7 icl: 0x0 flg: 0x0000
Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x01 0x1fa4 0x02 0x1f48 0x03 0x1ecc 0x04 0x1e70 0x05 0x1df4
0x06 0x1d90 0x07 0x1d20
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x7 slt: 0x15 objn: 73430(0x00011ed6) objd: 73430 tblspc: 4(0x00000004)
* 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: 0x00c005b9. 012c. 2d ctl max scn: 0x0000.000f4ed4 prv tx scn: 0x0000.000f4ee0
txn start scn: scn: 0x0000.000f53a9 logon user: 85
prev brb: 12584373 prev bcl: 0
KDO undo record:
KTB Redo
op: 0x03 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: Z
KDO Op code: DRP row dependencies Disabled --DRP操作完畢回滾
xtype: XA flags: 0x00000000 bdba: 0x0100047e hdba: 0x0100032a --bdba表示block address hdba 代表sgment header address
itli: 1 ispac: 0 maxfr: 4858
tabn: 0 slot: 0(0x0) - - - - - - - - - 這個slot表示這一行數據在數據塊中的行地址（行序列）
當中bdba表示file 4，block 1150 ,hdba表示file 4。block 810 與我們上面查詢出來的地址相符。
我們能夠看到，undo塊中並沒有直接保存rowid信息。可是oracle全然能夠依據上面的幾個信息（bdba,slot,objd)定位回滾時須要刪除的詳細數據，因此對於Insert操作，ORACLE僅僅需保留上述信息，就可以完畢回滾操作
三、基本概念和名詞解釋
- UBA: Undo block address
- RBA: Redo block address
- Dba: Data block address
- Rdba: Root dba
- Xid: Transaction ID
- ITL: Interested Transaction List 保存在數據塊的頭部（事務信息部分），包括XID,UBA,LCK。FLG等重要信息
Transaction Identifiers
Transaction identifiers (XID) uniquely identify a transaction within the system; they are used within the Interested Transaction List (ITL) of the data block.
A transaction identifier consists of:
- Undo segment number 即v$rollname中的usn
- Transaction table slot number 相應回滾段頭中回滾事務表的第幾條記錄
- Sequence number or wrap#
XID = usn# . slot# . wrap#
Undo Block Address
The undo block address (UBA) uniquely identifies the undo block for a given transaction; it is found within the ITL of the data block.
A UBA consists of:
- Data block address (DBA) of the block 前映像undo 塊地址
- The sequence number of the block 序列號
- The record number within the block undo記錄的開始地址（針對該塊）
UBA = DBA. seq#. rec#
四、從一個DML語句開始研究，SESSION A運行以下的語句，更新完畢后先不提交
（1）session A運行更新。更新兩條數據，例如以下
SQL
>
select
*
from undotest
where object_type
=
'PROCEDURE'
and id
in (
4703,
4704);
ID OBJECT_ID OBJECT_NAME OBJECT_TYPE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
4703 4771 SUBPTXT2 PROCEDURE
4704 4772 SUBPTXT PROCEDURE
SQL > update undotest set object_type = 'VIEW' where object_type = 'PROCEDURE' and id in ( 4703, 4704);
2 rows updated.
SQL > select * from undotest where id in ( 4703, 4704);
ID OBJECT_ID OBJECT_NAME OBJECT_TYPE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
4703 4771 SUBPTXT2 VIEW
4704 4772 SUBPTXT VIEW
ID OBJECT_ID OBJECT_NAME OBJECT_TYPE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
4703 4771 SUBPTXT2 PROCEDURE
4704 4772 SUBPTXT PROCEDURE
SQL > update undotest set object_type = 'VIEW' where object_type = 'PROCEDURE' and id in ( 4703, 4704);
2 rows updated.
SQL > select * from undotest where id in ( 4703, 4704);
ID OBJECT_ID OBJECT_NAME OBJECT_TYPE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
4703 4771 SUBPTXT2 VIEW
4704 4772 SUBPTXT VIEW
（2）查詢更新數據塊的信息和事務信息
s
QL
>
SELECT
2
dbms_rowid.rowid_object(rowid) object_id,
3 dbms_rowid.rowid_relative_fno(rowid) REL_FNO,
4 dbms_rowid.rowid_block_number(rowid) BLOCKNO,
5 dbms_rowid.rowid_row_number(rowid) ROWNO,rowid,id,object_name,object_type
6 FROM dh.undotest WHERE id in ( 4703, 4704);
OBJECT_ID REL_FNO BLOCKNO ROWNO ROWID ID OBJECT_NAME OBJECT_TYPE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
73424 4 195 70 AAAR7QAAEAAAADDABG 4703 SUBPTXT2 VIEW
73424 4 195 71 AAAR7QAAEAAAADDABH 4704 SUBPTXT VIEW
SQL > select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec,to_char(start_scnw, 'xxxxxxxx') start_scnw,
2 to_char(start_scnb, 'xxxxxxxx') start_scnb, start_scnb +start_scnw *power( 2, 32) start_scn
3 from v$ transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC START_SCNW START_SCNB START_SCN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
19 0 4 258 5 2 0 0 0
SQL > select name from v$rollname where usn = 19;
NAME
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
_SYSSMU19$
4 dbms_rowid.rowid_block_number(rowid) BLOCKNO,
5 dbms_rowid.rowid_row_number(rowid) ROWNO,rowid,id,object_name,object_type
6 FROM dh.undotest WHERE id in ( 4703, 4704);
OBJECT_ID REL_FNO BLOCKNO ROWNO ROWID ID OBJECT_NAME OBJECT_TYPE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
73424 4 195 70 AAAR7QAAEAAAADDABG 4703 SUBPTXT2 VIEW
73424 4 195 71 AAAR7QAAEAAAADDABH 4704 SUBPTXT VIEW
SQL > select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec,to_char(start_scnw, 'xxxxxxxx') start_scnw,
2 to_char(start_scnb, 'xxxxxxxx') start_scnb, start_scnb +start_scnw *power( 2, 32) start_scn
3 from v$ transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC START_SCNW START_SCNB START_SCN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
19 0 4 258 5 2 0 0 0
SQL > select name from v$rollname where usn = 19;
NAME
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
_SYSSMU19$
(3)刷新內存，dump數據塊,undo 段頭，undo block，例如以下
SQL
>
alter
system flush buffer_cache;
System altered.
SQL > oradebug
SQL > oradebug setmypid
Statement processed.
SQL > oradebug tracefile_name
/u01 /oracle /diag /rdbms /test /test /trace /test_ora_902.trc
SQL > alter system dump datafile 4 block 195;
System altered.
SQL > alter system dump undo header '_SYSSMU19$';
System altered.
SQL > alter system dump datafile 5 block 258;
System altered.
System altered.
SQL > oradebug
SQL > oradebug setmypid
Statement processed.
SQL > oradebug tracefile_name
/u01 /oracle /diag /rdbms /test /test /trace /test_ora_902.trc
SQL > alter system dump datafile 4 block 195;
System altered.
SQL > alter system dump undo header '_SYSSMU19$';
System altered.
SQL > alter system dump datafile 5 block 258;
System altered.
（4）分析數據塊dump文件
Block header dump: 0x010000c3
Object id on Block? Y
seg /obj: 0x11ed0 csc: 0x00.f2e95 itc: 3 flg: E typ: 1 - DATA
brn: 1 bdba: 0x10000b8 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn /Fsc
0x01 0xffff.000.00000000 0x00000000.0000.00 C - - - 0 scn 0x0000.000f2e95
0x02 0x0013.000. 00000004 0x01400102. 0001. 02 - - - - 2 fsc 0x000a.00000000
0x03 0x0000.000.00000000 0x00000000.0000.00 - - - - 0 fsc 0x0000.00000000
uba中undo record參數為2。即這個事務在這個數據塊上的變更（改動）產生的undo記錄（變更舊值記錄）在相應的undo數據塊中的開始地址（開始偏移量）
bdba: 0x010000c3
data_block_dump, data header at 0x2b0a86e2da7c
.....省略一部分..........
tab 0, row 70, @0x45f
tl: 25 fb: - -H -FL - - lb: 0x2 cc: 4 - - -這一行數據被鎖定，鎖定該行數據的事務為ITL事務槽中的第二個事務。
col 0: [ 3] c2 30 04
col 1: [ 3] c2 30 48
col 2: [ 8] 53 55 42 50 54 58 54 32
col 3: [ 4] 56 49 45 57
tab 0, row 71, @0x447
tl: 24 fb: - -H -FL - - lb: 0x2 cc: 4 - - -這一行數據被鎖定，鎖定該行數據的事務為ITL事務槽中的第二個事務。
Object id on Block? Y
seg /obj: 0x11ed0 csc: 0x00.f2e95 itc: 3 flg: E typ: 1 - DATA
brn: 1 bdba: 0x10000b8 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn /Fsc
0x01 0xffff.000.00000000 0x00000000.0000.00 C - - - 0 scn 0x0000.000f2e95
0x02 0x0013.000. 00000004 0x01400102. 0001. 02 - - - - 2 fsc 0x000a.00000000
0x03 0x0000.000.00000000 0x00000000.0000.00 - - - - 0 fsc 0x0000.00000000
uba中undo record參數為2。即這個事務在這個數據塊上的變更（改動）產生的undo記錄（變更舊值記錄）在相應的undo數據塊中的開始地址（開始偏移量）
bdba: 0x010000c3
data_block_dump, data header at 0x2b0a86e2da7c
.....省略一部分..........
tab 0, row 70, @0x45f
tl: 25 fb: - -H -FL - - lb: 0x2 cc: 4 - - -這一行數據被鎖定，鎖定該行數據的事務為ITL事務槽中的第二個事務。
col 0: [ 3] c2 30 04
col 1: [ 3] c2 30 48
col 2: [ 8] 53 55 42 50 54 58 54 32
col 3: [ 4] 56 49 45 57
tab 0, row 71, @0x447
tl: 24 fb: - -H -FL - - lb: 0x2 cc: 4 - - -這一行數據被鎖定，鎖定該行數據的事務為ITL事務槽中的第二個事務。
col 0: [ 3] c2 30 05
col 1: [ 3] c2 30 49
col 2: [ 7] 53 55 42 50 54 58 54
col 3: [ 4] 56 49 45 57
.........省略trace 文件里后面的輸出.............
（5）分析undo 段頭dump文件
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Undo Segment: _SYSSMU19$ (19)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Extent Control Header
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
............省略中間一部分................
Retention Table
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Extent Number: 0 Commit Time: 0
Extent Number: 1 Commit Time: 0
TRN CTL:: seq: 0x0001 chd: 0x0001 ctl: 0x0021 inc: 0x00000000 nfb: 0x0000
mgc: 0xb000 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x01400102.0001.01 scn: 0x0000.000e61e6
Undo Segment: _SYSSMU19$ (19)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Extent Control Header
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
............省略中間一部分................
Retention Table
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Extent Number: 0 Commit Time: 0
Extent Number: 1 Commit Time: 0
TRN CTL:: seq: 0x0001 chd: 0x0001 ctl: 0x0021 inc: 0x00000000 nfb: 0x0000
mgc: 0xb000 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x01400102.0001.01 scn: 0x0000.000e61e6
這個uba經過測試驗證，為事務表中最后（最新）一個事務的相應的undo block上的第一個undo record,即當這個回滾段頭存在多個事務時。這個uba表示最新的事務的uba地址，這個地址在整個事務的周期內不發生改變（除非這個回滾段頭上又分配了一個新的事務表）。因此，這個地址指向的是事務使用的第一個undo block
Version: 0x01
FREE BLOCK POOL::
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
TRN TBL::
index state cflags wrap# uel scn dba parent -xid nub stmt_num cmt
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x00 10 0x80 0x0004 0x0000 0x0000.00000000 0x01400102 0x0000.000.00000000 0x00000001 0x00000000 0
0x01 9 0x00 0x0003 0x0002 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x02 9 0x00 0x0003 0x0003 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x03 9 0x00 0x0003 0x0004 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
............省略中間一部分................
0x1f 9 0x00 0x0003 0x0020 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x20 9 0x00 0x0003 0x0021 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x21 9 0x00 0x0003 0xffff 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
Version: 0x01
FREE BLOCK POOL::
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
TRN TBL::
index state cflags wrap# uel scn dba parent -xid nub stmt_num cmt
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x00 10 0x80 0x0004 0x0000 0x0000.00000000 0x01400102 0x0000.000.00000000 0x00000001 0x00000000 0
0x01 9 0x00 0x0003 0x0002 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x02 9 0x00 0x0003 0x0003 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x03 9 0x00 0x0003 0x0004 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
............省略中間一部分................
0x1f 9 0x00 0x0003 0x0020 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x20 9 0x00 0x0003 0x0021 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x21 9 0x00 0x0003 0xffff 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
回想我們開始時查詢的事務XID信息：xidslot=0（這個事務占用UNDO事務表中第幾號事務槽） and xidseq=4 與上面標紅的0x00、state=10（代表事務狀態為活動）、wrap#=4 全然相符合。
當中dba列值表示包括這個事務的前映像的undo塊地址（事務最后更新的前映像UNDO地址）,與ITL事務槽中的uba地址一致 。即file 5,block 258(可使用dbms_utility.data_block_address_file函數轉換）
（6）分析UNDO block dump文件
UNDO BLK:
xid: 0x0013.000. 00000004 seq: 0x1 cnt: 0x2 irb: 0x2 icl: 0x0 flg: 0x0000
Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset - -undo信息偏移量,在undo塊中偏移
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x01 0x1f58 0x02 0x1ef4 - -當前undo塊中的最后一個偏移地址即Ox02 與irb一致
當中irb:0x2 表示未提交事務最新（最后運行的）變更相應的undo數據塊中的UNDO record地址，假設開始rollback，這是回滾的起點。
xid: 0x0013.000. 00000004 seq: 0x1 cnt: 0x2 irb: 0x2 icl: 0x0 flg: 0x0000
Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset - -undo信息偏移量,在undo塊中偏移
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x01 0x1f58 0x02 0x1ef4 - -當前undo塊中的最后一個偏移地址即Ox02 與irb一致
當中irb:0x2 表示未提交事務最新（最后運行的）變更相應的undo數據塊中的UNDO record地址，假設開始rollback，這是回滾的起點。
*-----------------------------
* Rec #0x1 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004) --依據Rec #0x2 中的rci記錄找到#0x1
* Layer: 11 (Row) opc: 1 rci 0x00 --rci指針為0。表示這是事務回滾過程中的最后一條記錄
Undo type: Regular undo Begin trans Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000Ext idx: 0
flg2: 0
*-----------------------------
uba: 0x00000000.0000.00 ctl max scn: 0x0000.000e61e6 prv tx scn: 0x0000.000e61e6
txn start scn: scn: 0x0000.00000000 logon user: 85
prev brb: 0 prev bcl: 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: 0x010000c3 hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 70(0x46) flag: 0x2c lock: 0 ckix: 80 --slot表示更新數據的行序列值（rowno），用於定位詳細的數據。與我們查詢的一致
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45 ---轉換為字符為‘PROCEDURE’。與我們更新前數據一致
轉換方法：
SELECT utl_raw.cast_to_varchar2(replace('50 52 4f 43 45 44 55 52 45',' ')) value FROM dual;
*-----------------------------
* Rec #0x2 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 (Row) opc: 1 rci 0x01 --指向REC# 0x01。即上一個偏移量
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
*-----------------------------
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post-11) padding: 1
op: C uba: 0x01400102.0001.01 --這個uba表示undo chain tx table。即同一update語句中的undo chain地址，這里為1，指向第一個偏移量。一個事務中的不同DML語句，無法通過該參數連接起來（形成undo chain）。由於該參數，不能跨越DML語句。
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000c3 hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 71(0x47) flag: 0x2c lock: 0 ckix: 80 --slot表示更新數據的行序列值（rowno），用於定位詳細的數據，與我們查詢的一致
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45 --與上面描寫敘述的一樣，轉換為字符為‘PROCEDURE’，與我們更新前數據一致
Rec #0x2 這條undo record中還記錄了一個rci參數，表示undo chain。同一個事務中的多次改動，依據這個chain連接起來。
當前rci參數值為0x01，即指向該undo塊中的第一個undo record,找到Rec #0x01 undo record后，檢查發現確實是我們這個UPDATE語句中的被更新的還有一條數據。
五、在SESSION A中繼續進行更新操作，進一步研究
（1）更新兩條數據。同一時候查詢主要的事務信息和數據塊信息
SQL
>
update undotest
set object_type
=
'VIEW'
where object_type
=
'PROCEDURE'
and id
in (
11504,
11505);
2 rows updated.
SQL > SELECT
2 dbms_rowid.rowid_object(rowid) object_id,
3 dbms_rowid.rowid_relative_fno(rowid) REL_FNO,
4 dbms_rowid.rowid_block_number(rowid) BLOCKNO,
5 dbms_rowid.rowid_row_number(rowid) ROWNO,rowid,id,object_name,object_type
6 FROM undotest WHERE id in ( 11504, 11505);
OBJECT_ID REL_FNO BLOCKNO ROWNO ROWID ID OBJECT_NAME OBJECT_TYPE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
73424 4 236 41 AAAR7QAAEAAAADsAAp 11504 DBMS_FEATURE_RMAN_BZ PROCEDURE
IP2
73424 4 236 42 AAAR7QAAEAAAADsAAq 11505 DBMS_FEATURE_RMAN_BA PROCEDURE
SIC
SQL > select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec,to_char(start_scnw, 'xxxxxxxx') start_scnw,
2 to_char(start_scnb, 'xxxxxxxx') start_scnb, start_scnb +start_scnw *power( 2, 32) start_scn
3 from v$ transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC START_SCNW START_SCNB START_SCN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
19 0 4 258 5 4 0 0 0
SQL > alter system flush buffer_cache;
System altered.
SQL > alter system dump datafile 4 block 195;
System altered.
SQL > alter system dump datafile 4 block 236;
System altered.
SQL > alter system dump undo header '_SYSSMU19$';
System altered.
SQL > alter system dump datafile 5 block 258;
System altered.
2 rows updated.
SQL > SELECT
2 dbms_rowid.rowid_object(rowid) object_id,
3 dbms_rowid.rowid_relative_fno(rowid) REL_FNO,
4 dbms_rowid.rowid_block_number(rowid) BLOCKNO,
5 dbms_rowid.rowid_row_number(rowid) ROWNO,rowid,id,object_name,object_type
6 FROM undotest WHERE id in ( 11504, 11505);
OBJECT_ID REL_FNO BLOCKNO ROWNO ROWID ID OBJECT_NAME OBJECT_TYPE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
73424 4 236 41 AAAR7QAAEAAAADsAAp 11504 DBMS_FEATURE_RMAN_BZ PROCEDURE
IP2
73424 4 236 42 AAAR7QAAEAAAADsAAq 11505 DBMS_FEATURE_RMAN_BA PROCEDURE
SIC
SQL > select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec,to_char(start_scnw, 'xxxxxxxx') start_scnw,
2 to_char(start_scnb, 'xxxxxxxx') start_scnb, start_scnb +start_scnw *power( 2, 32) start_scn
3 from v$ transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC START_SCNW START_SCNB START_SCN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
19 0 4 258 5 4 0 0 0
SQL > alter system flush buffer_cache;
System altered.
SQL > alter system dump datafile 4 block 195;
System altered.
SQL > alter system dump datafile 4 block 236;
System altered.
SQL > alter system dump undo header '_SYSSMU19$';
System altered.
SQL > alter system dump datafile 5 block 258;
System altered.
（2）分析數據塊dump文件
能夠看到。SESSION A事務中第一個update語句改動的數據塊（datafile 4 block 195）沒有不論什么改變
Block header dump: 0x010000c3
Object id on Block?
Block header dump: 0x010000c3
Object id on Block?
Y
seg/obj: 0x11ed0 csc: 0x00.f2e95 itc: 3 flg: E typ: 1 - DATA
brn: 1 bdba: 0x10000b8 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0xffff.000.00000000 0x00000000.0000.00 C--- 0 scn 0x0000.000f2e95
0x02 0x0013.000.00000004 0x01400102.0001.02 ---- 2 fsc 0x000a.00000000
0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000
bdba: 0x010000c3
data_block_dump,data header at 0x2b5f5d4e6a7c
.........省略trace 文件里后面的輸出.............
事務中第二個update語句改動的數據塊（4。236）上的事務信息與我們查詢的一致，例如以下
Block header dump: 0x010000ec
Object id on Block?
Y
seg/obj: 0x11ed0 csc: 0x00.f2e95 itc: 3 flg: E typ: 1 - DATA
brn: 0 bdba: 0x10000e8 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0xffff.000.00000000 0x00000000.0000.00 C--- 0 scn 0x0000.000f2e95
0x02 0x0013.000.00000004 0x01400102.0001.04 ---- 2 fsc 0x000a.00000000
0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000
bdba: 0x010000ec
data_block_dump,data header at 0x2b5f5d4e6a7c
..........省略一部分..........
tab 0, row 41, @0x38f
tl: 42 fb: --H-FL-- lb: 0x2 cc: 4
col 0: [ 4] c3 02 10 05
col 1: [ 4] c3 02 13 03
col 2: [23]
44 42 4d 53 5f 46 45 41 54 55 52 45 5f 52 4d 41 4e 5f 42 5a 49 50 32
col 3: [ 4] 56 49 45 57
tab 0, row 42, @0x365
tl: 42 fb: --H-FL-- lb: 0x2 cc: 4
col 0: [ 4] c3 02 10 06
col 1: [ 4] c3 02 13 04
col 2: [23]
.........省略trace 文件里后面的輸出.............
（3）分析undo 段頭dump文件
Undo Segment: _SYSSMU19$ (19)
********************************************************************************
...............省略一部分..............
TRN CTL:: seq: 0x0001 chd: 0x0001 ctl: 0x0021 inc: 0x00000000 nfb: 0x0000
mgc: 0xb000 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x01400102.0001.01 scn: 0x0000.000e61e6
Version: 0x01
FREE BLOCK POOL::
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
TRN TBL::
index state cflags wrap# uel scn dba parent-xid nub stmt_num cmt
------------------------------------------------------------------------------------------------
0x00 10 0x80 0x0004 0x0000 0x0000.00000000 0x01400102 0x0000.000.00000000 0x00000001 0x00000000 0
0x01 9 0x00 0x0003 0x0002 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x02 9 0x00 0x0003 0x0003 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x03 9 0x00 0x0003 0x0004 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x04 9 0x00 0x0003 0x0005 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x05 9 0x00 0x0003 0x0006 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
.........省略trace 文件里后面的輸出.............
********************************************************************************
...............省略一部分..............
TRN CTL:: seq: 0x0001 chd: 0x0001 ctl: 0x0021 inc: 0x00000000 nfb: 0x0000
mgc: 0xb000 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x01400102.0001.01 scn: 0x0000.000e61e6
Version: 0x01
FREE BLOCK POOL::
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
TRN TBL::
index state cflags wrap# uel scn dba parent-xid nub stmt_num cmt
------------------------------------------------------------------------------------------------
0x00 10 0x80 0x0004 0x0000 0x0000.00000000 0x01400102 0x0000.000.00000000 0x00000001 0x00000000 0
0x01 9 0x00 0x0003 0x0002 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x02 9 0x00 0x0003 0x0003 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x03 9 0x00 0x0003 0x0004 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x04 9 0x00 0x0003 0x0005 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x05 9 0x00 0x0003 0x0006 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
.........省略trace 文件里后面的輸出.............
undo段頭上的事務表沒有發生改變
（4）分析undo block dump文件
UNDO BLK:
xid: 0x0013.000. 00000004 seq: 0x1 cnt: 0x4 irb: 0x4 icl: 0x0 flg: 0x0000
Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x01 0x1f58 0x02 0x1ef4 0x03 0x1e98 0x04 0x1e34
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x1 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* 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: 0x00000000.0000.00 ctl max scn: 0x0000.000e61e6 prv tx scn: 0x0000.000e61e6
txn start scn: scn: 0x0000.00000000 logon user: 85
prev brb: 0 prev bcl: 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: 0x010000c3 hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 70(0x46) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x2 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x01
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.01
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000c3 hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 71(0x47) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x3 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x02
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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: 0x010000ec hdba: 0x010000aa --bdba：4,236。即我們update語句改動的數據塊，與查詢出來的信息一致
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 41(0x29) flag: 0x2c lock: 0 ckix: 0
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45 ---轉換為字符為‘PROCEDURE’，與我們更新前數據一致
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x4 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x03
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.03 --新發起的update語句，uba參數值與第一條不同（ Rec #0x2 undo record記錄） ，事務中的每一個DML語句保存自己的uba，用於語句回滾
xid: 0x0013.000. 00000004 seq: 0x1 cnt: 0x4 irb: 0x4 icl: 0x0 flg: 0x0000
Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x01 0x1f58 0x02 0x1ef4 0x03 0x1e98 0x04 0x1e34
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x1 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* 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: 0x00000000.0000.00 ctl max scn: 0x0000.000e61e6 prv tx scn: 0x0000.000e61e6
txn start scn: scn: 0x0000.00000000 logon user: 85
prev brb: 0 prev bcl: 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: 0x010000c3 hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 70(0x46) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x2 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x01
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.01
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000c3 hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 71(0x47) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x3 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x02
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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: 0x010000ec hdba: 0x010000aa --bdba：4,236。即我們update語句改動的數據塊，與查詢出來的信息一致
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 41(0x29) flag: 0x2c lock: 0 ckix: 0
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45 ---轉換為字符為‘PROCEDURE’，與我們更新前數據一致
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x4 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x03
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.03 --新發起的update語句，uba參數值與第一條不同（ Rec #0x2 undo record記錄） ，事務中的每一個DML語句保存自己的uba，用於語句回滾
KDO Op code: URP
row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ec hdba: 0x010000aa - -bdba： 4, 236。即我們 update語句改動的數據塊，與查詢出來的信息一致
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 42(0x2a) flag: 0x2c lock: 0 ckix: 0
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45 - - -轉換為字符為‘ PROCEDURE’，與我們更新前數據一致
End dump data blocks tsn: 6 file#: 5 minblk 258 maxblk 258
xtype: XA flags: 0x00000000 bdba: 0x010000ec hdba: 0x010000aa - -bdba： 4, 236。即我們 update語句改動的數據塊，與查詢出來的信息一致
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 42(0x2a) flag: 0x2c lock: 0 ckix: 0
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45 - - -轉換為字符為‘ PROCEDURE’，與我們更新前數據一致
End dump data blocks tsn: 6 file#: 5 minblk 258 maxblk 258
六、再次在SESSION A中進行更新，當事務使用的undo block超過一個1個時，分析整個事務的undo record是怎么串聯起來。
（1）在session A 中繼續更新undotest，並查看事務信息
SQL
>
update undotest
set object_type
=
'VIEW'
where object_type
=
'TABLE'
and rownum
<
99;
98 rows updated.
SQL > select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec,to_char(start_scnw, 'xxxxxxxx') start_scnw,
2 to_char(start_scnb, 'xxxxxxxx') start_scnb, start_scnb +start_scnw *power( 2, 32) start_scn
3 from v$ transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC START_SCNW START_SCNB START_SCN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
19 0 4 259 5 20 0 0 0
UBABLK之前為258，如今查詢出來為259，因此能夠肯定眼下事務使用已經超過一個UNDO block。
98 rows updated.
SQL > select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec,to_char(start_scnw, 'xxxxxxxx') start_scnw,
2 to_char(start_scnb, 'xxxxxxxx') start_scnb, start_scnb +start_scnw *power( 2, 32) start_scn
3 from v$ transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC START_SCNW START_SCNB START_SCN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
19 0 4 259 5 20 0 0 0
UBABLK之前為258，如今查詢出來為259，因此能夠肯定眼下事務使用已經超過一個UNDO block。
（2）DUMP 段頭，undo 塊，data block，這里就不再列舉出來
SQL
>
alter
system flush buffer_cache;
System altered.
SQL > alter system dump datafile 5 block 259;
System altered.
SQL > alter system dump undo header '_SYSSMU19$';
System altered.
System altered.
SQL > alter system dump datafile 5 block 259;
System altered.
SQL > alter system dump undo header '_SYSSMU19$';
System altered.
（3）分析dump 出來的trace 文件
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*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
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*
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*
Undo Segment: _SYSSMU19$ ( 19)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Extent Control Header
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Extent Header:: spare1: 0 spare2: 0 #extents: 2 #blocks: 15
last map 0x00000000 #maps: 0 offset: 4080
Highwater:: 0x01400103 ext#: 0 blk#: 2 ext size: 7
#blocks in seg. hdr's freelists: 0
#blocks below: 0
mapblk 0x00000000 offset: 0
Unlocked
Map Header:: next 0x00000000 #extents: 2 obj#: 0 flag: 0x40000000
Extent Map
-----------------------------------------------------------------
0x01400101 length: 7
0x01400108 length: 8
Retention Table
-----------------------------------------------------------
Extent Number:0 Commit Time: 0
Extent Number:1 Commit Time: 0
TRN CTL:: seq: 0x0001 chd: 0x0001 ctl: 0x0021 inc: 0x00000000 nfb: 0x0000
mgc: 0xb000 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x01400102.0001.01 scn: 0x0000.000e61e6
Version: 0x01
FREE BLOCK POOL::
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
TRN TBL::
index state cflags wrap# uel scn dba parent-xid nub stmt_num cmt
------------------------------------------------------------------------------------------------
0x00 10 0x80 0x0004 0x0000 0x0000.00000000 0x01400103 0x0000.000.00000000 0x00000002 0x00000000 0
0x01 9 0x00 0x0003 0x0002 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x02 9 0x00 0x0003 0x0003 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x03 9 0x00 0x0003 0x0004 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
.........省略trace 文件里后面的輸出.............
能夠看到dba的地址已經發生改變。指向最新使用的undo block地址。即datafile 5,block 259
Undo Segment: _SYSSMU19$ ( 19)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Extent Control Header
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Extent Header:: spare1: 0 spare2: 0 #extents: 2 #blocks: 15
last map 0x00000000 #maps: 0 offset: 4080
Highwater:: 0x01400103 ext#: 0 blk#: 2 ext size: 7
#blocks in seg. hdr's freelists: 0
#blocks below: 0
mapblk 0x00000000 offset: 0
Unlocked
Map Header:: next 0x00000000 #extents: 2 obj#: 0 flag: 0x40000000
Extent Map
-----------------------------------------------------------------
0x01400101 length: 7
0x01400108 length: 8
Retention Table
-----------------------------------------------------------
Extent Number:0 Commit Time: 0
Extent Number:1 Commit Time: 0
TRN CTL:: seq: 0x0001 chd: 0x0001 ctl: 0x0021 inc: 0x00000000 nfb: 0x0000
mgc: 0xb000 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x01400102.0001.01 scn: 0x0000.000e61e6
Version: 0x01
FREE BLOCK POOL::
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
uba: 0x00000000.0000.00 ext: 0x0 spc: 0x0
TRN TBL::
index state cflags wrap# uel scn dba parent-xid nub stmt_num cmt
------------------------------------------------------------------------------------------------
0x00 10 0x80 0x0004 0x0000 0x0000.00000000 0x01400103 0x0000.000.00000000 0x00000002 0x00000000 0
0x01 9 0x00 0x0003 0x0002 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x02 9 0x00 0x0003 0x0003 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
0x03 9 0x00 0x0003 0x0004 0x0000.000e61e6 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
.........省略trace 文件里后面的輸出.............
能夠看到dba的地址已經發生改變。指向最新使用的undo block地址。即datafile 5,block 259
（4）分析undo block trace
1.以下是undo block datafile 5 block 259的dump trace文件
UNDO BLK:
xid: 0x0013.000. 00000004 seq: 0x1 cnt: 0x14 irb: 0x14 icl: 0x0 flg: 0x0000
Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x01 0x1f88 0x02 0x1f28 0x03 0x1ec8 0x04 0x1e68 0x05 0x1e08
0x06 0x1da8 0x07 0x1d48 0x08 0x1ce8 0x09 0x1c88 0x0a 0x1c28
0x0b 0x1bc8 0x0c 0x1b68 0x0d 0x1b08 0x0e 0x1aa8 0x0f 0x1a48
0x10 0x19e8 0x11 0x1988 0x12 0x1928 0x13 0x18c8 0x14 0x1868
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x1 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x00
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x01400102
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.52 - -當一個事務使用多個undo block時，事務使用的undo塊順序，是依據這個參數串聯起來，即undo chain
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 201(0xc9) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x2 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x01
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400103.0001.01
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 205(0xcd) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.................省略一部分................
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x13 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x12
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400103. 0001. 12
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 239(0xef) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x14 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004) --這個相應irb參數：0x14，也相應ITL中的UBA第三個參數：undo record的開始地址。
UNDO BLK:
xid: 0x0013.000. 00000004 seq: 0x1 cnt: 0x14 irb: 0x14 icl: 0x0 flg: 0x0000
Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0x01 0x1f88 0x02 0x1f28 0x03 0x1ec8 0x04 0x1e68 0x05 0x1e08
0x06 0x1da8 0x07 0x1d48 0x08 0x1ce8 0x09 0x1c88 0x0a 0x1c28
0x0b 0x1bc8 0x0c 0x1b68 0x0d 0x1b08 0x0e 0x1aa8 0x0f 0x1a48
0x10 0x19e8 0x11 0x1988 0x12 0x1928 0x13 0x18c8 0x14 0x1868
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x1 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x00
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x01400102
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.52 - -當一個事務使用多個undo block時，事務使用的undo塊順序，是依據這個參數串聯起來，即undo chain
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 201(0xc9) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x2 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x01
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400103.0001.01
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 205(0xcd) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.................省略一部分................
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x13 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x12
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400103. 0001. 12
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 239(0xef) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x14 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004) --這個相應irb參數：0x14，也相應ITL中的UBA第三個參數：undo record的開始地址。
* Layer: 11 (Row) opc: 1 rci 0x13
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
*-----------------------------
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post-11) padding: 1
op: C uba: 0x01400103.0001.13
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 241(0xf1) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45 ---轉化為字符，能夠發現與我們更新的舊值同樣。符合我們的語氣
End dump data blocks tsn: 6 file#: 5 minblk 259 maxblk 259
2.以下是undo block datafile 5 block 258（事務使用的第一個undo block）的dump trace文件
我們能夠看到例如以下內容（省略無用信息）， 注意undo record中的uba參數
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x4 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x03
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.03
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ec hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 42(0x2a) flag: 0x2c lock: 0 ckix: 0
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x5 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x04
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
我們能夠看到例如以下內容（省略無用信息）， 注意undo record中的uba參數
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x4 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x03
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.03
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ec hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 42(0x2a) flag: 0x2c lock: 0 ckix: 0
ncol: 4 nnew: 1 size: 5
col 3: [ 9] 50 52 4f 43 45 44 55 52 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x5 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x04
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
Rec #0x5 記錄時我們最后一個update語句使用的第一個undo記錄，我們能夠看到。該記錄中並沒有保存事務中上一條語句使用的uba，因此我們能夠知道。undo record中的uba參數無法跨越語句，僅僅能在單個語句中將undo記錄串聯起來
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x6 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x05
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.05
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 2(0x2) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* Rec #0x6 slt: 0x00 objn: 73424(0x00011ed0) objd: 73424 tblspc: 4(0x00000004)
* Layer: 11 ( Row) opc: 1 rci 0x05
Undo type: Regular undo Last buffer split: No
Temp Object: No
Tablespace Undo: No
rdba: 0x00000000
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post - 11) padding: 1
op: C uba: 0x01400102.0001.05
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x010000ab hdba: 0x010000aa
itli: 2 ispac: 0 maxfr: 4858
tabn: 0 slot: 2(0x2) flag: 0x2c lock: 0 ckix: 80
ncol: 4 nnew: 1 size: 1
col 3: [ 5] 54 41 42 4c 45
七、一些結論
- UNDO段頭中TRN CTL的uba參數：UNDO段頭的事務表中最后（最新）一個事務的相應的undo block上的第一個undo record,即當這個回滾段頭存在多個事務時，這個uba表示最新的事務的uba地址，這個地址在整個事務的周期內不發生改變（除非這個回滾段頭上又分配了一個新的事務表），因此。這個地址指向的是事務使用的第一個undo block；
- UNDO BLOCK中undo record記錄中的uba參數：假設事務中的一個DML語句須要使用多個undo record，則這個參數指向的是前一個undo record的記錄。通過這個參數能夠形成同一個DML語句的undo chain tx table。可是一個事務中的不同DML語句，無法通過該參數連接起來（形成undo chain）。由於該參數，不能跨越DML語句。當一個事務使用多個undo block時。事務使用的undo塊順序。是依據這個參數串聯起來；
- 數據塊頭的ITL中的uba參數：指向事務在這個數據塊上的變更（改動）所使用的undo塊中的最后一個undo record偏移量地址，針對這個數據塊改動，這個uba是回滾的起點。
- UNDO record中的bdba表示block address 。hdba表示 segment header address
- undo塊中不會直接保存rowid信息，可是oracle全然能夠undo record中幾個信息（bdba,slot,objd),生成數據變更是的詳細地址（rowid）；
- 一個事務所使用的undo記錄順序是通過undo record中的uba參數、rci參數，undo塊上的irb,itl中的uba共同起作用來串聯變更的順序，事務的回滾也是依據這個undo chain按順序完畢。
當中最關鍵的兩個參數：undo record中的uba 形成單個dml語句的undo chain,rci參數能夠跨越DML語句，能夠指向事務中前一個dml語句使用的undo record。
最后部分事實上有幾張原理圖想要附上，供大家更清晰的了解。只是不知道怎么上傳到博客，有須要的朋友直接給我留言吧