[20180306]数据块检查和2.txt
--//昨天测试修改检查和偏移为0x0(偏移在16,17字节),在修改前面的15字节为0,一般数据块可以通过检查.
--//链接:http://blog.itpub.net/267265/viewspace-2151524/
--//今天测试如果数据块在system表空间的情况下会是否可行.
1.环境:
SCOTT@book> @ &r/ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
SCOTT@book> create table system.deptx tablespace system as select * from dept;
Table created.
SCOTT@book> select rowid,deptx.* from system.deptx where deptno=10;
ROWID DEPTNO DNAME LOC
------------------ ---------- -------------- -------------
AAAWGYAABAAAAl5AAA 10 ACCOUNTING NEW YORK
SCOTT@book> @ &r/rowid AAAWGYAABAAAAl5AAA
OBJECT FILE BLOCK ROW ROWID_DBA DBA TEXT
---------- ---------- ---------- ---------- -------------------- -------------------- ----------------------------------------
90520 1 2425 0 0x400979 1,2425 alter system dump datafile 1 block 2425
BBED> sum dba 1,2425
Check value for File 1, Block 2425:
current = 0x41f3, required = 0x41f3
--//当前检查和41f3.
2.关闭数据库修改看看:
SYS@book> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
--//修改对应信息:
BBED> p chkval_kcbh
ub2 chkval_kcbh @16 0x41f3
BBED> p flg_kcbh
ub1 flg_kcbh @15 0x04 (KCBHFCKV)
BBED> assign kcbh.flg_kcbh=0x0
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
ub1 flg_kcbh @15 0x00 (NONE)
BBED> assign kcbh.chkval_kcbh=0x0
ub2 chkval_kcbh @16 0x0000
BBED> sum dba 1,2425
Check value for File 1, Block 2425:
current = 0x0000, required = 0x0000
3.启动数据库看看:
SYS@book> startup
ORACLE instance started.
Total System Global Area 638910464 bytes
Fixed Size 2255832 bytes
Variable Size 201327656 bytes
Database Buffers 427819008 bytes
Redo Buffers 7507968 bytes
Database mounted.
Database opened.
SYS@book> select rowid,deptx.* from system.deptx where deptno=10;
ROWID DEPTNO DNAME LOC
------------------ ---------- -------------- -------------
AAAWGYAABAAAAl5AAA 10 ACCOUNTING NEW YORK
SYS@book> alter system flush buffer_cache;
System altered.
BBED> set dba 1,2425
DBA 0x00400979 (4196729 1,2425)
BBED> sum
Check value for File 1, Block 2425:
current = 0x0000, required = 0x0000
--//一样可行.看来理解存在问题.算一下这个时候检查和是多少.
BBED> set dba 1,2425
DBA 0x00400979 (4196729 1,2425)
BBED> assign kcbh.flg_kcbh=0x4
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
ub1 flg_kcbh @15 0x04 (KCBHFCKV)
BBED> sum
Check value for File 1, Block 2425:
current = 0x0000, required = 0x41f3
--//可以看出bbed的检查和算法,如果kcbh.flg_kcbh=0x0,估计跳过检查和计算.
--//2425*8192 = 19865600
$ xxd -c16 -g 2 -s 19865600 -l 8192 /mnt/ramdisk/book/system01.dbf | cut -c10-50 | xor.sh
..
xor result: F345
--//可以发现跳过了检查和检查.
BBED> set dba 1,2425
DBA 0x00400979 (4196729 1,2425)
BBED> assign kcbh.flg_kcbh=0x4
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
ub1 flg_kcbh @15 0x04 (KCBHFCKV)
BBED> assign kcbh.chkval_kcbh=0x41f3
ub2 chkval_kcbh @16 0x41f3
--//修改回来.
$ xxd -c16 -g 2 -s 19865600 -l 8192 /mnt/ramdisk/book/system01.dbf | cut -c10-50 | xor.sh
...
xor result: 0
--//这样就正确了.也许对文件头不行,不测试了.
--//xor.sh脚本参考链接:http://blog.itpub.net/267265/viewspace-2134945/
