[20160528]bbed观察行目录变化.txt
如果使用bbed观察kdbr,可以发现记录的是相对偏移量,这个偏移我一直认为从kdbh算起.而对于数据块前面有ITL槽信息,对于有2个ITL的块,
使用assm的表空间,一般我看到都是100.如果一个块上有多个事务,ITL槽会增加,kdbh的地址就会发生变化,这样记录在kdbr的行目录信息
就存在变化,通过例子来说明:
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
create table t (id number,name varchar2(20));
insert into t select rownum ,'aaaa' from dual connect by level<=4;
commit ;
SCOTT@book> select ora_rowscn,rowid,t.* from t;
ORA_ROWSCN ROWID ID NAME
------------ ------------------ ------------ --------------------
13237974561 AAAW8VAAEAAAAIkAAA 1 aaaa
13237974561 AAAW8VAAEAAAAIkAAB 2 aaaa
13237974561 AAAW8VAAEAAAAIkAAC 3 aaaa
13237974561 AAAW8VAAEAAAAIkAAD 4 aaaa
SCOTT@book> @ &r/rowid AAAW8VAAEAAAAIkAAA
OBJECT FILE BLOCK ROW DBA TEXT
------------ ------------ ------------ ------------ -------------------- ----------------------------------------
93973 4 548 0 4,548 alter system dump datafile 4 block 548 ;
SCOTT@book> alter system checkpoint;
System altered.
2.通过bbed观察:
BBED> set dba 4,548
DBA 0x01000224 (16777764 4,548)
BBED> p kdbr
sb2 kdbr[0] @118 8044
sb2 kdbr[1] @120 8055
sb2 kdbr[2] @122 8066
sb2 kdbr[3] @124 8077
BBED> p *kdbr[0]
rowdata[0]
----------
ub1 rowdata[0] @8144 0x2c
BBED> x /rnc
rowdata[0] @8144
----------
flag@8144: 0x2c (KDRHFL, KDRHFF, KDRHFH)
lock@8145: 0x01
cols@8146: 2
col 0[2] @8147: 1
col 1[4] @8150: aaaa
--注意看看kdbr[0]与实际的偏移相差100.
BBED> map
File: /mnt/ramdisk/book/users01.dbf (4)
Block: 548 Dba:0x01000224
------------------------------------------------------------
KTB Data Block (Table/Cluster)
struct kcbh, 20 bytes @0
struct ktbbh, 72 bytes @20
struct kdbh, 14 bytes @100
struct kdbt[1], 4 bytes @114
sb2 kdbr[4] @118
ub1 freespace[8018] @126
ub1 rowdata[44] @8144
ub4 tailchk @8188
--注意看kdbh的偏移是100.如果一个块有多个事务,itl槽会增加.看看情况.
--session 1:注意不要提交.我的update前后字段长度没有变化,也就是原地替换.
update t set name='1111' where id=1;
--session 2:
update t set name='2222' where id=2;
--session 3:
update t set name='3333' where id=3;
SCOTT@book> alter system checkpoint;
System altered.
3.再次观察数据块(注意bbed要退出在进入):
BBED> set dba 4,548
DBA 0x01000224 (16777764 4,548)
BBED> p kdbr
sb2 kdbr[0] @142 8020
sb2 kdbr[1] @144 8031
sb2 kdbr[2] @146 8042
sb2 kdbr[3] @148 8053
--如果与前面对比可以发现记录的偏移量减少了24.正好是ITL槽的长度.不知道oracle为什么这样设计,如果记录的是绝对偏移量,不是减
--少许多计算吗?
BBED> map
File: /mnt/ramdisk/book/users01.dbf (4)
Block: 548 Dba:0x01000224
------------------------------------------------------------
KTB Data Block (Table/Cluster)
struct kcbh, 20 bytes @0
struct ktbbh, 96 bytes @20
struct kdbh, 14 bytes @124
struct kdbt[1], 4 bytes @138
sb2 kdbr[4] @142
ub1 freespace[7994] @150
ub1 rowdata[44] @8144
ub4 tailchk @8188
--可以发现kdbh现在的偏移是124,因为增加一个ITL槽.
BBED> p ktbbh
struct ktbbh, 96 bytes @20
ub1 ktbbhtyp @20 0x01 (KDDBTDATA)
union ktbbhsid, 4 bytes @24
ub4 ktbbhsg1 @24 0x00016f15
ub4 ktbbhod1 @24 0x00016f15
struct ktbbhcsc, 8 bytes @28
ub4 kscnbas @28 0x150b76aa
ub2 kscnwrp @32 0x0003
sb2 ktbbhict @36 3
ub1 ktbbhflg @38 0x32 (NONE)
ub1 ktbbhfsl @39 0x00
ub4 ktbbhfnx @40 0x01000220
struct ktbbhitl[0], 24 bytes @44
struct ktbitxid, 8 bytes @44
ub2 kxidusn @44 0x0009
ub2 kxidslt @46 0x0014
ub4 kxidsqn @48 0x0000327d
struct ktbituba, 8 bytes @52
ub4 kubadba @52 0x00c00305
ub2 kubaseq @56 0x06a9
ub1 kubarec @58 0x10
ub2 ktbitflg @60 0x0001 (NONE)
union _ktbitun, 2 bytes @62
sb2 _ktbitfsc @62 0
ub2 _ktbitwrp @62 0x0000
ub4 ktbitbas @64 0x00000000
struct ktbbhitl[1], 24 bytes @68
struct ktbitxid, 8 bytes @68
ub2 kxidusn @68 0x000a
ub2 kxidslt @70 0x001b
ub4 kxidsqn @72 0x00009dc4
struct ktbituba, 8 bytes @76
ub4 kubadba @76 0x00c00e44
ub2 kubaseq @80 0x1e7f
ub1 kubarec @82 0x0c
ub2 ktbitflg @84 0x0001 (NONE)
union _ktbitun, 2 bytes @86
sb2 _ktbitfsc @86 0
ub2 _ktbitwrp @86 0x0000
ub4 ktbitbas @88 0x00000000
struct ktbbhitl[2], 24 bytes @92
struct ktbitxid, 8 bytes @92
ub2 kxidusn @92 0x0008
ub2 kxidslt @94 0x001b
ub4 kxidsqn @96 0x0000236b
struct ktbituba, 8 bytes @100
ub4 kubadba @100 0x00c000ca
ub2 kubaseq @104 0x0761
ub1 kubarec @106 0x02
ub2 ktbitflg @108 0x0001 (NONE)
union _ktbitun, 2 bytes @110
sb2 _ktbitfsc @110 0
ub2 _ktbitwrp @110 0x0000
ub4 ktbitbas @112 0x00000000
--现在是3个ITL槽.
BBED> p kdbh
struct kdbh, 14 bytes @124
ub1 kdbhflag @124 0x00 (NONE)
sb1 kdbhntab @125 1
sb2 kdbhnrow @126 4
sb2 kdbhfrre @128 -1
sb2 kdbhfsbo @130 26
sb2 kdbhfseo @132 8020
sb2 kdbhavsp @134 7994
sb2 kdbhtosp @136 7994
--在补充前面的学习,人为修改kdbhavsp=7993.
BBED> assign kdbhavsp=7993
sb2 kdbhavsp @134 7993
BBED> sum apply
Check value for File 4, Block 548:
current = 0xf388, required = 0xf388
BBED> verify
DBVERIFY - Verification starting
FILE = /mnt/ramdisk/book/users01.dbf
BLOCK = 548
Block Checking: DBA = 16777764, Block Type = KTB-managed data block
data header at 0x7f3b9b8af27c
kdbchk: the amount of space used is not equal to block size
used=70 fsc=0 avsp=7993 dtl=8064
Block 548 failed with check code 6110
--可以对比我以前的测试dtl不再是8088,而是8064,减少了24字节.
-- [20160527]快速提交的一个疑问.txt http://blog.itpub.net/267265/viewspace-2108017/
-- // dtl - used +fsc
-- // 8064-70+0=7994
-- used 可以这样计算
SCOTT@book> select 8064-8020+14+4+8 from dual ;
8064-8020+14+4+8
----------------
70
BBED> map
File: /mnt/ramdisk/book/users01.dbf (4)
Block: 548 Dba:0x01000224
------------------------------------------------------------
KTB Data Block (Table/Cluster)
struct kcbh, 20 bytes @0
struct ktbbh, 96 bytes @20
struct kdbh, 14 bytes @124
struct kdbt[1], 4 bytes @138
sb2 kdbr[4] @142
ub1 freespace[7994] @150
ub1 rowdata[44] @8144
ub4 tailchk @8188
-- 说明: kdbh 占用14 ,kdbt[1] 占用4 , kdbr[4 占用8个字节.
