直接看实验吧。
-----block dump
从上面block dump我们可以看到，有一个未提交事务：
0x02 0x000e.025.00000176 0x0240439e.015b.2f ---- 1 fsc 0x0017.00000000
0x02： 表示第2个itl
0x000e.025.00000176 表示xid，xid的结构= 回滚段编号14+事务槽编号37+序号374
0x0240439e.015b.2f 表示UBA，uba的结构= undo block adress+Sequence + last enrty of undo block
=(file 9 block 17310)+347+47
Flag 表示该事务的状态，事务状态有如下几种：
------undo segment header dump
###### 提交该事务
此时trace信息如下：
----undo segment header dump
事务提交以后，此时的scn：
block scn： 004310ae --> 4395182
itl scn： 0x0017.004310ae -->4395182
undo segment scn(事务表上slot scn)：0x0000.004310ae -->4395182
从上面的实验我们可以看出，当事务commit以后，oracle会更新如下3处SCN，且保证是一致的：
block scn,itl scn,undo segment header slot scn.
注意：
1. 上面的实验是针对fast commit cleanout的，我们知道block cleanout有2种方式，其中之一就是
fast commit cleanout，另外一种是延迟块清除，也就是delayed block cleanout。
2. 如果发生延迟块清除，那么在事务commit以后，不会去更新block scn和block 内itl scn，
而是仅仅更新undo segment header scn solt scn。
3. 针对block 里面scn和itl scn的更改，这里有涉及到slot重用的问题，这里有分为2种情况：
1)无slot重用时，发生延迟块清除,block内scn和itl scn是根据undo 段头事务表的信息来进行更新的。
2)当时发生slot重用时，block scn被更新为延迟块清除时刻的scn，block itl scn会更新为control scn。
##### 下面来看延迟块清除的情况
-----block dump
----undo segment header dump
下面用mos提供的一个脚本来进行slot重用实验，进而观察block scn，itl scn和undo scn的变化。
此时我们来dump data block和undo segment header
--- data block dump
-----undo header dump
我们可以看到，此时undo control scn的值是等于block scn和block itl scn的，进而也验证了前面的观点。
SQL> conn roger/roger
Connected.
SQL> set lines 150
SQL> create table tab_undo as select owner,object_name,object_id from
2 sys.dba_objects where object_id < 10;
Table created.
SQL> select * from tab_undo;
OWNER OBJECT_NAME OBJECT_ID
------------------------------ ------------------------------ ----------
SYS I_FILE#_BLOCK# 9
SYS C_FILE#_BLOCK# 8
SYS I_TS# 7
SYS C_TS# 6
SYS CLU$ 5
SYS TAB$ 4
SYS I_OBJ# 3
SYS C_OBJ# 2
8 rows selected.
SQL> select dbms_rowid.rowid_relative_fno(rowid) file#,
2 dbms_rowid.rowid_block_number(rowid) blk#
3 from tab_undo;
FILE# BLK#
---------- ----------
4 6444
4 6444
4 6444
4 6444
4 6444
4 6444
4 6444
4 6444
8 rows selected.
SQL> delete from tab_undo where object_id=9;
1 row deleted.
SQL> select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec from v$transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC
---------- ---------- ---------- ---------- ---------- ----------
14 37 374 17310 9 47
SQL> select usn,name from v$rollname where usn=14;
USN NAME
---------- ------------------------------
14 _SYSSMU14$
SQL> alter system dump datafile 4 block 6444;
System altered.
SQL> select count(*) from tab_undo;
COUNT(*)
----------
7
SQL> alter system dump undo header '_SYSSMU14$';
System altered.
-----block dump
Start dump data blocks tsn: 4 file#: 4 minblk 6444 maxblk 6444
buffer tsn: 4 rdba: 0x0100192c (4/6444)
scn: 0x0000.00430d30 seq: 0x01 flg: 0x04 tail: 0x0d300601
frmt: 0x02 chkval: 0x097f type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
Dump of memory from 0xB7349600 to 0xB734B600
B7349600 0000A206 0100192C 00430D30 04010000 [....,...0.C.....]
......省略部分内容
B734B5F0 425F2345 4B434F4C 0AC10223 0D300601 [E#_BLOCK#.....0.]
Block header dump: 0x0100192c
Object id on Block? Y
seg/obj: 0xdd9b csc: 0x00.430ce1 itc: 3 flg: E typ: 1 - DATA
brn: 0 bdba: 0x1001929 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 0x0000.00430ce1
0x02 0x000e.025.00000176 0x0240439e.015b.2f ---- 1 fsc 0x0017.00000000
0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000
data_block_dump,data header at 0xb734967c
===============
tsiz: 0x1f80
hsiz: 0x22
pbl: 0xb734967c
bdba: 0x0100192c
76543210
flag=--------
ntab=1
nrow=8
frre=-1
fsbo=0x22
fseo=0x1eee
avsp=0x1ecc
tosp=0x1ee5
0xe:pti[0] nrow=8 offs=0
0x12:pri[0] offs=0x1f67
0x14:pri[1] offs=0x1f4e
0x16:pri[2] offs=0x1f3e
0x18:pri[3] offs=0x1f2e
0x1a:pri[4] offs=0x1f1f
0x1c:pri[5] offs=0x1f10
0x1e:pri[6] offs=0x1eff
0x20:pri[7] offs=0x1eee
block_row_dump:
从上面block dump我们可以看到，有一个未提交事务：
0x02 0x000e.025.00000176 0x0240439e.015b.2f ---- 1 fsc 0x0017.00000000
0x02： 表示第2个itl
0x000e.025.00000176 表示xid，xid的结构= 回滚段编号14+事务槽编号37+序号374
0x0240439e.015b.2f 表示UBA，uba的结构= undo block adress+Sequence + last enrty of undo block
=(file 9 block 17310)+347+47
Flag 表示该事务的状态，事务状态有如下几种：
------undo segment header dump
TRN CTL:: seq: 0x015b chd: 0x000f ctl: 0x002d inc: 0x00000000 nfb: 0x0000
mgc: 0x8201 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x0240439e.015b.2f scn: 0x0000.00430671
Version: 0x01
FREE BLOCK POOL::
uba: 0x00000000.015b.2e ext: 0x27 spc: 0x542
uba: 0x00000000.015b.18 ext: 0x27 spc: 0x153e
uba: 0x00000000.0148.16 ext: 0x14 spc: 0xf62
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 9 0x00 0x0177 0x0017 0x0000.00430978 0x02404391 0x0000.000.00000000 0x00000001 0x00000000 1343542242
...........
0x24 9 0x00 0x0175 0x0028 0x0000.004306b5 0x0240438e 0x0000.000.00000000 0x00000001 0x00000000 1343541622
0x25 10 0x80 0x0176 0x0027 0x0000.00430ce7 0x0240439e 0x0000.000.00000000 0x00000001 0x00000000 0
0x26 9 0x00 0x0174 0x0003 0x0000.004306a3 0x0240438e 0x0000.000.00000000 0x00000001 0x00000000 1343541622
..........
0x2f 9 0x00 0x0175 0x0016 0x0000.004306ff 0x0240438e 0x0000.000.00000000 0x00000001 0x00000000 1343541622
SQL> select dbms_utility.data_block_address_file(TO_NUMBER('240439e', 'XXXXXXXX')) file_id,
2 dbms_utility.data_block_address_block(TO_NUMBER('240439e', 'XXXXXXXX')) block_id from dual;
FILE_ID BLOCK_ID
---------- ----------
9 17310
SQL>
0x25 --转换为10进制为37，也就是我们所看到的XIDSLOT值。
此时：
block scn ：00430d30 --> 4394288
itl scn： 0x0017.00000000
undo segment scn(事务表上slot scn)：0x0000.00430ce7 -->4394215
###### 提交该事务
SQL> commit;
Commit complete.
SQL> select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec from v$transaction;
no rows selected
SQL>
再次dump data block和undo header block
SQL> alter system dump datafile 4 block 6444;
System altered.
SQL> alter system dump undo header '_SYSSMU14$';
System altered.
SQL>
此时trace信息如下：
*** 2012-07-28 23:52:22.995
Start dump data blocks tsn: 4 file#: 4 minblk 6444 maxblk 6444
buffer tsn: 4 rdba: 0x0100192c (4/6444)
scn: 0x0000.004310ae seq: 0x01 flg: 0x02 tail: 0x10ae0601
frmt: 0x02 chkval: 0x0000 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
Dump of memory from 0xB7349600 to 0xB734B600
......省略部分信息
Block header dump: 0x0100192c
Object id on Block? Y
seg/obj: 0xdd9b csc: 0x00.430ce1 itc: 3 flg: E typ: 1 - DATA
brn: 0 bdba: 0x1001929 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 0x0000.00430ce1
0x02 0x000e.025.00000176 0x0240439e.015b.2f --U- 1 fsc 0x0017.004310ae --该事务已经commit
0x03 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000
data_block_dump,data header at 0xb734967c
===============
tsiz: 0x1f80
hsiz: 0x22
pbl: 0xb734967c
bdba: 0x0100192c
76543210
flag=--------
ntab=1
nrow=8
frre=-1
fsbo=0x22
fseo=0x1eee
avsp=0x1ecc
tosp=0x1ee5
0xe:pti[0] nrow=8 offs=0
0x12:pri[0] offs=0x1f67
0x14:pri[1] offs=0x1f4e
0x16:pri[2] offs=0x1f3e
0x18:pri[3] offs=0x1f2e
0x1a:pri[4] offs=0x1f1f
0x1c:pri[5] offs=0x1f10
0x1e:pri[6] offs=0x1eff
0x20:pri[7] offs=0x1eee
block_row_dump:
tab 0, row 0, @0x1f67
tl: 2 fb: --HDFL-- lb: 0x2 ---这是被delete的行
tab 0, row 1, @0x1f4e
tl: 25 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [ 3] 53 59 53
col 1: [14] 43 5f 46 49 4c 45 23 5f 42 4c 4f 43 4b 23
col 2: [ 2] c1 09
tab 0, row 2, @0x1f3e
tl: 16 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [ 3] 53 59 53
col 1: [ 5] 49 5f 54 53 23
col 2: [ 2] c1 08
.....省略部分信息
tl: 17 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [ 3] 53 59 53
col 1: [ 6] 43 5f 4f 42 4a 23
col 2: [ 2] c1 03
end_of_block_dump
End dump data blocks tsn: 4 file#: 4 minblk 6444 maxblk 6444
----undo segment header dump
TRN CTL:: seq: 0x015b chd: 0x000f ctl: 0x0025 inc: 0x00000000 nfb: 0x0001
mgc: 0x8201 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x0240439e.015b.2f scn: 0x0000.00430671
Version: 0x01
FREE BLOCK POOL::
uba: 0x0240439e.015b.2f ext: 0x27 spc: 0x494
uba: 0x00000000.015b.18 ext: 0x27 spc: 0x153e
uba: 0x00000000.0148.16 ext: 0x14 spc: 0xf62
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 9 0x00 0x0177 0x0017 0x0000.00430978 0x02404391 0x0000.000.00000000 0x00000001 0x00000000 1343542242
.........省略部分信息
0x24 9 0x00 0x0175 0x0028 0x0000.004306b5 0x0240438e 0x0000.000.00000000 0x00000001 0x00000000 1343541622
0x25 9 0x00 0x0176 0xffff 0x0000.004310ae 0x0240439e 0x0000.000.00000000 0x00000001 0x00000000 1343544689
0x26 9 0x00 0x0174 0x0003 0x0000.004306a3 0x0240438e 0x0000.000.00000000 0x00000001 0x00000000 1343541622
.........省略部分信息
0x2f 9 0x00 0x0175 0x0016 0x0000.004306ff 0x0240438e 0x0000.000.00000000 0x00000001 0x00000000 1343541622
可以看到，第25个事务已经提交了,state 9 表示非活动事务。
事务提交以后，此时的scn：
block scn： 004310ae --> 4395182
itl scn： 0x0017.004310ae -->4395182
undo segment scn(事务表上slot scn)：0x0000.004310ae -->4395182
从上面的实验我们可以看出，当事务commit以后，oracle会更新如下3处SCN，且保证是一致的：
block scn,itl scn,undo segment header slot scn.
注意：
1. 上面的实验是针对fast commit cleanout的，我们知道block cleanout有2种方式，其中之一就是
fast commit cleanout，另外一种是延迟块清除，也就是delayed block cleanout。
2. 如果发生延迟块清除，那么在事务commit以后，不会去更新block scn和block 内itl scn，
而是仅仅更新undo segment header scn solt scn。
3. 针对block 里面scn和itl scn的更改，这里有涉及到slot重用的问题，这里有分为2种情况：
1)无slot重用时，发生延迟块清除,block内scn和itl scn是根据undo 段头事务表的信息来进行更新的。
2)当时发生slot重用时，block scn被更新为延迟块清除时刻的scn，block itl scn会更新为control scn。
##### 下面来看延迟块清除的情况
---为了模拟更容易，创建较小的undo tablespace
SQL> create undo tablespace undotbs2 datafile
2 '/home/ora10g/oradata/roger/undotb2_01.dbf' size 1m;
Tablespace created.
SQL> alter system set undo_tablespace=undotbs2;
System altered.
SQL>
SQL> select dbms_rowid.rowid_block_number(rowid),ora_rowscn,object_id from tab_undo;
DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID) ORA_ROWSCN OBJECT_ID
------------------------------------ ---------- ----------
6444 4395182 8
6444 4395182 7
6444 4395182 6
6444 4395182 5
6444 4395182 4
6444 4395182 3
6444 4395182 2
7 rows selected.
SQL>
SQL> select dbms_rowid.rowid_block_number(rowid),ora_rowscn,object_id from tab_undo;
DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID) ORA_ROWSCN OBJECT_ID
------------------------------------ ---------- ----------
6444 4395182 8
6444 4395182 7
6444 4395182 6
6444 4395182 5
6444 4395182 4
6444 4395182 3
6444 4395182 2
7 rows selected.
SQL> update tab_undo set OBJECT_ID=100 where object_id=8;
1 row updated.
SQL> select xidusn,xidslot,xidsqn,ubablk,ubafil,ubarec from v$transaction;
XIDUSN XIDSLOT XIDSQN UBABLK UBAFIL UBAREC
---------- ---------- ---------- ---------- ---------- ----------
25 0 2 59 6 1
SQL> select usn,name from v$rollname where usn=25;
USN NAME
---------- ------------------------------
25 _SYSSMU25$
SQL> alter system flush buffer_cache;
System altered.
SQL> ----首先将cache buffer中的脏块全部写入到disk中，然后再commit。
SQL> show user
USER is "ROGER"
SQL> alter system dump datafile 4 block 6444;
System altered.
SQL> alter system dump undo header '_SYSSMU25$';
System altered.
SQL> commit;
Commit complete.
SQL> select timestamp_to_scn(systimestamp) from dual ;
TIMESTAMP_TO_SCN(SYSTIMESTAMP)
------------------------------
4398117
-----block dump
Start dump data blocks tsn: 4 file#: 4 minblk 6444 maxblk 6444
buffer tsn: 4 rdba: 0x0100192c (4/6444)
scn: 0x0000.00431bec seq: 0x01 flg: 0x00 tail: 0x1bec0601
frmt: 0x02 chkval: 0x0000 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
Dump of memory from 0xB7349600 to 0xB734B600
......省略部分信息
Block header dump: 0x0100192c
Object id on Block? Y
seg/obj: 0xdd9b csc: 0x00.430ce1 itc: 3 flg: E typ: 1 - DATA
brn: 0 bdba: 0x1001929 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 0x0000.00430ce1
0x02 0x000e.025.00000176 0x0240439e.015b.2f --U- 1 fsc 0x0017.004310ae
0x03 0x0019.000.00000002 0x0180003b.0000.01 ---- 1 fsc 0x0000.00000000
data_block_dump,data header at 0xb734967c
===============
tsiz: 0x1f80
hsiz: 0x22
pbl: 0xb734967c
bdba: 0x0100192c
76543210
flag=--------
ntab=1
nrow=8
frre=-1
fsbo=0x22
fseo=0x1eee
avsp=0x1ecc
tosp=0x1ee5
0xe:pti[0] nrow=8 offs=0
0x12:pri[0] offs=0x1f67
0x14:pri[1] offs=0x1f4e
0x16:pri[2] offs=0x1f3e
0x18:pri[3] offs=0x1f2e
0x1a:pri[4] offs=0x1f1f
0x1c:pri[5] offs=0x1f10
0x1e:pri[6] offs=0x1eff
0x20:pri[7] offs=0x1eee
block_row_dump:
----undo segment header dump
TRN CTL:: seq: 0x0000 chd: 0x0001 ctl: 0x002f inc: 0x00000000 nfb: 0x0000
mgc: 0x8201 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x0180003b.0000.01 scn: 0x0000.00000000
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 0x0002 0x0000 0x0000.00431b82 0x0180003b 0x0000.000.00000000 0x00000001 0x00000000 0
0x01 9 0x00 0x0001 0x0002 0x0000.00000000 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
......省略部分信息
0x2f 9 0x00 0x0001 0xffff 0x0000.00000000 0x00000000 0x0000.000.00000000 0x00000000 0x00000000 0
下面用mos提供的一个脚本来进行slot重用实验，进而观察block scn，itl scn和undo scn的变化。
SQL> show user
USER is "ROGER"
SQL> alter system dump datafile 4 block 6444;
System altered.
SQL> alter system dump undo header '_SYSSMU25$';
System altered.
SQL> commit;
Commit complete.
SQL> select timestamp_to_scn(systimestamp) from dual ;
TIMESTAMP_TO_SCN(SYSTIMESTAMP)
------------------------------
4398117
SQL> show user
USER is "SYS"
SQL> create table goon AS select * from dba_objects where 1 = 2;
Table created.
SQL> create or replace procedure proc_go_break_reuse(v_XIDUSN number,
2 v_XIDSLOT number,
3 v_XIDSQN number)
4 /* ————————————————–
5 Create_user :Mecoyoo
6 Time:2008-5-08
7 Description:It’s used to make transaction slot reused
8 —————————————————*/
9 AS
10 nsid number;
11 type transaction_record_type is record(
12 XIDUSN number,
13 XIDSLOT number,
14 XIDSQN number);
15 transaction_record transaction_record_type;
16 begin
17 select sys_context('userenv','sid') into nsid from dual;
18 loop
19 insert into goon
20 select * from dba_objects where rownum < 100;
21 select XIDUSN, XIDSLOT, XIDSQN
22 into transaction_record
23 from v$transaction a, v$session b
24 where a.ADDR = b.TADDR
25 and b.SID = nsid;
26 if (transaction_record.XIDUSN = v_XIDUSN and
27 transaction_record.XIDSLOT = v_XIDSLOT and
28 transaction_record.XIDSQN > v_XIDSQN) then
29 goto resue_end;
30 end if;
31 commit;
32 delete from goon;
33 select XIDUSN, XIDSLOT, XIDSQN
34 into transaction_record
35 from v$transaction a, v$session b
36 where a.ADDR = b.TADDR
37 and b.SID = nsid;
38 if (transaction_record.XIDUSN = v_XIDUSN and
39 transaction_record.XIDSLOT = v_XIDSLOT and
40 transaction_record.XIDSQN > v_XIDSQN) then
41 goto resue_end;
42 end if;
43 commit;
44 end loop;
45 <>
46 commit;
47 end;
48 /
Procedure created.
SQL>
SQL> show user
USER is "SYS"
SQL> exec proc_go_break_reuse(25,0,2);
PL/SQL procedure successfully completed.
SQL> conn roger/roger
Connected.
SQL> col object_name for a20
SQL> set lines 150
SQL> select * from tab_undo;
OWNER OBJECT_NAME OBJECT_ID
------------------------------ -------------------- ----------
SYS C_FILE#_BLOCK# 100
SYS I_TS# 7
SYS C_TS# 6
SYS CLU$ 5
SYS TAB$ 4
SYS I_OBJ# 3
SYS C_OBJ# 2
7 rows selected.
SQL> select timestamp_to_scn(systimestamp) from dual;
TIMESTAMP_TO_SCN(SYSTIMESTAMP)
------------------------------
4399930
SQL>
SQL> select dbms_rowid.rowid_block_number(rowid),ora_rowscn,object_id from tab_undo;
DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID) ORA_ROWSCN OBJECT_ID
------------------------------------ ---------- ----------
6444 4398116 100
6444 4398116 7
6444 4398116 6
6444 4398116 5
6444 4398116 4
6444 4398116 3
6444 4398116 2
7 rows selected.
SQL>
SQL> alter system dump datafile 4 block 6444;
System altered.
SQL> alter system dump undo header '_SYSSMU25$';
System altered.
此时我们来dump data block和undo segment header
--- data block dump
Start dump data blocks tsn: 4 file#: 4 minblk 6444 maxblk 6444
buffer tsn: 4 rdba: 0x0100192c (4/6444)
scn: 0x0000.00431c24 seq: 0x01 flg: 0x06 tail: 0x1c240601
frmt: 0x02 chkval: 0x065e type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
.....省略部分信息
Block header dump: 0x0100192c
Object id on Block? Y
seg/obj: 0xdd9b csc: 0x00.430ce1 itc: 3 flg: E typ: 1 - DATA
brn: 0 bdba: 0x1001929 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 0x0000.00430ce1
0x02 0x000e.025.00000176 0x0240439e.015b.2f --U- 1 fsc 0x0017.004310ae
0x03 0x0019.000.00000002 0x0180003b.0000.01 --U- 1 fsc 0x0000.00431c24 ---这里itl scn等于前面的block scn了
data_block_dump,data header at 0xd0d987c
===============
tsiz: 0x1f80
hsiz: 0x22
pbl: 0x0d0d987c
bdba: 0x0100192c
76543210
flag=--------
ntab=1
nrow=8
frre=-1
fsbo=0x22
fseo=0x1eee
avsp=0x1ecc
tosp=0x1ee5
0xe:pti[0] nrow=8 offs=0
0x12:pri[0] offs=0x1f67
0x14:pri[1] offs=0x1f4e
0x16:pri[2] offs=0x1f3e
0x18:pri[3] offs=0x1f2e
0x1a:pri[4] offs=0x1f1f
0x1c:pri[5] offs=0x1f10
0x1e:pri[6] offs=0x1eff
0x20:pri[7] offs=0x1eee
-----undo header dump
TRN CTL:: seq: 0x0008 chd: 0x0001 ctl: 0x0000 inc: 0x00000000 nfb: 0x0001
mgc: 0x8201 xts: 0x0068 flg: 0x0001 opt: 2147483646 (0x7ffffffe)
uba: 0x01800040.0008.1f scn: 0x0000.00431c24 ---等于block scn值
Version: 0x01
FREE BLOCK POOL::
uba: 0x01800040.0008.21 ext: 0x0 spc: 0x9f0
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 9 0x00 0x0003 0xffff 0x0000.0043232c 0x01800040 0x0000.000.00000000 0x00000001 0x00000000 1343551357
0x01 9 0x00 0x0002 0x0002 0x0000.00431c5e 0x0180003b 0x0000.000.00000000 0x00000001 0x00000000 1343550861
0x02 9 0x00 0x0002 0x0003 0x0000.00431c6c 0x0180003b 0x0000.000.00000000 0x00000001 0x00000000 1343550861
......省略部分信息
0x2f 9 0x00 0x0002 0x0000 0x0000.00432320 0x01800040 0x0000.000.00000000 0x00000001 0x00000000 1343551357
0043232c 转换为10进制为： 4399916
我们可以看到，此时undo control scn的值是等于block scn和block itl scn的，进而也验证了前面的观点。
「喜欢这篇文章，您的关注和赞赏是给作者最好的鼓励」
关注作者
【版权声明】本文为墨天轮用户原创内容，转载时必须标注文章的来源（墨天轮），文章链接，文章作者等基本信息，否则作者和墨天轮有权追究责任。如果您发现墨天轮中有涉嫌抄袭或者侵权的内容，欢迎发送邮件至：contact@modb.pro进行举报，并提供相关证据，一经查实，墨天轮将立刻删除相关内容。
