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在上一篇修改datablock itl(bbed模拟提交事务一之修改itl)的基础之上，本篇实现修改undo segment header中的相关事务槽信息,从而屏蔽数据库在重启或者进程异常的时候,smon的回滚操作,从而比较完美的实现了手工提交数据库事务
update table and uncommit(session 1)
SQL> select distinct
2 dbms_rowid.rowid_relative_fno(rowid) rel_fno,
3 dbms_rowid.rowid_block_number(rowid) block_no
4 from chf.t_xifenfei;
REL_FNO BLOCK_NO
---------- ----------
4 28
SQL> select * from chf.t_xifenfei;
OBJECT_ID OBJECT_NAME
---------- --------------------
20 xifenfei.com
44 xifenfei.com
28 xifenfei.com
15 xifenfei.com
29 xifenfei.com
3 xifenfei.com
25 xifenfei.com
39 xifenfei.com
51 xifenfei.com
26 xifenfei.com
17 xifenfei.com
13 xifenfei.com
9 xifenfei.com
41 xifenfei.com
48 I_CON1
38 I_OBJ3
7 I_TS#
53 I_CDEF4
19 IND$
19 rows selected.
SQL> update chf.t_xifenfei set object_name='orasos.com' where rownum<10;
9 rows updated.
SQL> select * from chf.t_xifenfei;
OBJECT_ID OBJECT_NAME
---------- --------------------
20 orasos.com
44 orasos.com
28 orasos.com
15 orasos.com
29 orasos.com
3 orasos.com
25 orasos.com
39 orasos.com
51 orasos.com
26 xifenfei.com
17 xifenfei.com
13 xifenfei.com
9 xifenfei.com
41 xifenfei.com
48 I_CON1
38 I_OBJ3
7 I_TS#
53 I_CDEF4
19 IND$
19 rows selected.
dump undo header(session 2)
SQL> alter system flush buffer_cache;
System altered.
SQL> alter system checkpoint;
System altered.
SQL> SELECT XIDUSN,XIDSLOT,XIDSQN,UBAFIL,UBABLK,UBASQN,UBAREC FROM v$transaction;
XIDUSN XIDSLOT XIDSQN UBAFIL UBABLK UBASQN UBAREC
---------- ---------- ---------- ---------- ---------- ---------- ----------
1 13 367 2 1126 362 32
SQL> alter system dump undo header "_SYSSMU1$";
System altered.
index state cflags wrap# uel scn dba parent-xid nub stmt_num cmt
------------------------------------------------------------------------------------------------------------------
…………
0x0c 9 0x00 0x016e 0x0029 0x0b2c.c02d1f6a 0x00800464 0x0000.000.00000000 0x00000001 0x00000000 1358813163
0x0d 10 0x80 0x016f 0x0002 0x0b2c.c02d7b15 0x00800466 0x0000.000.00000000 0x00000001 0x00000000 0
0x0e 9 0x00 0x016f 0x000f 0x0b2c.c02d2ae2 0x00800466 0x0000.000.00000000 0x00000001 0x00000000 1358820065
…………
通过结合dump undo header 中的TRN TBL的state为10的为active事务,然后结合scn/dba等信息,
来确定是哪条记录是需要我们修改.然后通过find命令快速定位到0x0d这条记录,然后进行修改
通过结合bbed的dump命令得出16进制数据分析得出如下结论
--index 0x0c 6e01 0000 64048000 6a1f2dc0 2c0b0000 09 00 2900 0000000000000000 00000000 01000000 ebd7fd50(1358813163注意存储顺序) --index 0x0d 6f01 wrap# 0000 66048000 dba 157b2dc0 2c0b0000 scn 0a state 80 cflags 0200 uel 0000000000000000 parent-xid 00000000 stmt_num 01000000 nub 00000000 cmt --index 0x0e 6f01 0000 66048000 e22a2dc0 2c0b0000 09 00 0f00 0000000000000000 00000000 01000000 e1f2fd50(1358820065)
bbed modify undo segment header(session 2)
BBED> f /x 0a80 File: /u01/oracle/oradata/XFF/undotbs01.dbf (0) Block: 9 Offsets: 6736 to 6751 Dba:0x00000000 ------------------------------------------------------------------------ 0a800200 00000000 00000000 00000000 <32 bytes per line> BBED> m /x 0900 Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y File: /u01/oracle/oradata/XFF/undotbs01.dbf (0) Block: 9 Offsets: 6736 to 6751 Dba:0x00000000 ------------------------------------------------------------------------ 09000200 00000000 00000000 00000000 <32 bytes per line> BBED> sum apply Check value for File 0, Block 9: current = 0xecdd, required = 0xecdd
bbed modify data block itl(session 2)
struct ktbbhitl[0], 24 bytes @44
struct ktbitxid, 8 bytes @44
ub2 kxidusn @44 0x0001
ub2 kxidslt @46 0x000d
ub4 kxidsqn @48 0x0000016f
struct ktbituba, 8 bytes @52
ub4 kubadba @52 0x00800466
ub2 kubaseq @56 0x016a
ub1 kubarec @58 0x20
ub2 ktbitflg @60 0x0009 (NONE)
union _ktbitun, 2 bytes @62
b2 _ktbitfsc @62 18
ub2 _ktbitwrp @62 0x0012
ub4 ktbitbas @64 0x00000000
BBED> m /x 0080 offset 60
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
File: /u01/oracle/oradata/XFF/users01.dbf (0)
Block: 28 Offsets: 60 to 571 Dba:0x00000000
------------------------------------------------------------------------
00801200 00000000 09002a00 36020000
<32 bytes per line>
BBED> sum apply
Check value for File 0, Block 28:
current = 0xccf1, required = 0xccf1
restart db and select table(session 3)
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 306184192 bytes
Fixed Size 1267164 bytes
Variable Size 109054500 bytes
Database Buffers 188743680 bytes
Redo Buffers 7118848 bytes
Database mounted.
Database opened.
SQL> col object_name for a20
SQL> set pages 100
SQL> select * from chf.t_xifenfei;
OBJECT_ID OBJECT_NAME
---------- --------------------
20 orasos.com
44 orasos.com
28 orasos.com
15 orasos.com
29 orasos.com
3 orasos.com
25 orasos.com
39 orasos.com
51 orasos.com
26 xifenfei.com
17 xifenfei.com
13 xifenfei.com
9 xifenfei.com
41 xifenfei.com
48 I_CON1
38 I_OBJ3
7 I_TS#
53 I_CDEF4
19 IND$
19 rows selected.
到此证明,通过修改undo segment header中的state和cflags实现数据库启动不回滚未提交事务；通过修改datablock itl实现数据库在访问未提交数据块时候不访问undo。从而整体上较完美的实现了手工提交一个事务(数据库提交一个事务涉及的方方面面较为复杂，这里只是通过修改最核心的两部分来大致模拟提交事务)
如何精确获得段头的Block地址,如undoo1.dbf的_SYSSMU13_3953822434$的块号
通过bbed 定位到行，然后r 的方式查看，或者借助第三方工具定位到行号