数据块内部偏移量的基本计算方法

BASE的计算方法为：
对于ASSM：76+（itc-1) * 24= 52 + itc * 24
对于MSSM：68+（itc-1) * 24= 44 + itc * 24

gyj@ZMDB> select * from v$type_size where component in ('KCB','KTB');

COMPONEN TYPE DESCRIPTION TYPE_SIZE
-------- -------- -------------------------------- ----------
KCB KCBH BLOCK COMMON HEADER 20
KTB KTBIT TRANSACTION VARIABLE HEADER 24
KTB KTBBH TRANSACTION FIXED HEADER 48
KTB KTBBH_BS TRANSACTION BLOCK BITMAP SEGMENT 8

1、我们先对ASSM做测试

gyj@ZMDB> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production

gyj@ZMDB> create tablespace assm datafile '/u01/app/oracle/oradata/zmdb/assm01.dbf' size 50M;

Tablespace created.

gyj@ZMDB> create table gyj_t5(id int,name varchar2(100)) tablespace assm;

Table created.

gyj@ZMDB> insert into gyj_t5 values(1,'AAAAA');

1 row created.

gyj@ZMDB> insert into gyj_t5 values(2,'BBBBB');

1 row created.

gyj@ZMDB> insert into gyj_t5 values(3,'CCCCC');

1 row created.

gyj@ZMDB> COMMIT;

Commit complete.

gyj@ZMDB> alter system flush buffer_cache;

System altered.

gyj@ZMDB> select dbms_rowid.rowid_relative_fno(rowid) file#,dbms_rowid.rowid_block_number(rowid) block#,id,name from gyj_t5;

     FILE# BLOCK# ID NAME
---------- ---------- ---------- ----------
        10 135 1 AAAAA
        10 135 2 BBBBB
        10 135 3 CCCCC


BBED> set file 10 block 135
        FILE# 10
        BLOCK# 135

BBED> p kdbr[0]
sb2 kdbr[0] @118 8076

BBED> p *kdbr[0]
rowdata[24]
-----------
ub1 rowdata[24] @8176 0x2c

BBED> x /rnc
rowdata[24] @8176
-----------
flag@8176: 0x2c (KDRHFL, KDRHFF, KDRHFH)
lock@8177: 0x01
cols@8178: 2

col 0[2] @8179: 1
col 1[5] @8182: AAAAA

BBED> p ktbbhict
sb2 ktbbhict @36 2

8176-8076=76+（itc-1) * 24= 76+（2-1）* 24=100

2、我们对MSSM做测试

gyj@ZMDB> create tablespace mssm datafile '/u01/app/oracle/oradata/zmdb/mssm01.dbf' size 50M segment space management manual;

Tablespace created.


gyj@ZMDB> create table gyj_mssm(id int,name varchar2(100)) tablespace mssm;

Table created.

gyj@ZMDB> insert into gyj_mssm values(4,'DDDDD');

1 row created.

gyj@ZMDB> insert into gyj_mssm values(5,'EEEEE');

1 row created.

gyj@ZMDB> insert into gyj_mssm values(6,'FFFFF');

1 row created.

gyj@ZMDB> commit;

Commit complete.


gyj@ZMDB> col name for a20
gyj@ZMDB> select dbms_rowid.rowid_relative_fno(rowid) file#,dbms_rowid.rowid_block_number(rowid) block#,id,name from gyj_mssm;

     FILE# BLOCK# ID NAME
---------- ---------- ---------- --------------------
        11 129 4 DDDDD
        11 129 5 EEEEE
        11 129 6 FFFFF

BBED> set file 11 block 129
        FILE# 11
        BLOCK# 129

BBED> p kdbr[0]
sb2 kdbr[0] @110 8084

BBED> p *kdbr[0]
rowdata[24]
-----------
ub1 rowdata[24] @8176 0x2c

BBED> x /rnc
rowdata[24] @8176
-----------
flag@8176: 0x2c (KDRHFL, KDRHFF, KDRHFH)
lock@8177: 0x01
cols@8178: 2

col 0[2] @8179: 4
col 1[5] @8182: DDDDD

BBED> p ktbbhict
sb2 ktbbhict @36 2

8176-8084=68+（itc-1) * 24=68+（2-1）*24=92

3、为什么ASSM要比MSSM多了8个字节

************MSSM
BBED> set file 11 block 129
        FILE# 11
        BLOCK# 129

BBED> map /v
 File: /u01/app/oracle/oradata/zmdb/mssm01.dbf (11)
 Block: 129 Dba:0x02c00081
------------------------------------------------------------
 KTB Data Block (Table/Cluster)

 struct kcbh, 20 bytes @0
    ub1 type_kcbh @0
    ub1 frmt_kcbh @1
    ub1 spare1_kcbh @2
    ub1 spare2_kcbh @3
    ub4 rdba_kcbh @4
    ub4 bas_kcbh @8
    ub2 wrp_kcbh @12
    ub1 seq_kcbh @14
    ub1 flg_kcbh @15
    ub2 chkval_kcbh @16
    ub2 spare3_kcbh @18

 struct ktbbh, 72 bytes @20
    ub1 ktbbhtyp @20
    union ktbbhsid, 4 bytes @24
    struct ktbbhcsc, 8 bytes @28
    sb2 ktbbhict @36
    ub1 ktbbhflg @38
    ub1 ktbbhfsl @39
    ub4 ktbbhfnx @40
    struct ktbbhitl[2], 48 bytes @44

 struct kdbh, 14 bytes @92
    ub1 kdbhflag @92
    sb1 kdbhntab @93
    sb2 kdbhnrow @94
    sb2 kdbhfrre @96
    sb2 kdbhfsbo @98
    sb2 kdbhfseo @100
    sb2 kdbhavsp @102
    sb2 kdbhtosp @104

 struct kdbt[1], 4 bytes @106
    sb2 kdbtoffs @106
    sb2 kdbtnrow @108

 sb2 kdbr[3] @110

 ub1 freespace[8036] @116

 ub1 rowdata[36] @8152

 ub4 tailchk @8188

*****************ASSM
BBED> set file 10 block 135
        FILE# 10
        BLOCK# 135

File: /u01/app/oracle/oradata/zmdb/assm01.dbf (10)
 Block: 141 Dba:0x0280008d
------------------------------------------------------------
 KTB Data Block (Table/Cluster)

 struct kcbh, 20 bytes @0
    ub1 type_kcbh @0
    ub1 frmt_kcbh @1
    ub1 spare1_kcbh @2
    ub1 spare2_kcbh @3
    ub4 rdba_kcbh @4
    ub4 bas_kcbh @8
    ub2 wrp_kcbh @12
    ub1 seq_kcbh @14
    ub1 flg_kcbh @15
    ub2 chkval_kcbh @16
    ub2 spare3_kcbh @18

 struct ktbbh, 72 bytes @20
    ub1 ktbbhtyp @20
    union ktbbhsid, 4 bytes @24
    struct ktbbhcsc, 8 bytes @28
    sb2 ktbbhict @36
    ub1 ktbbhflg @38
    ub1 ktbbhfsl @39
    ub4 ktbbhfnx @40
    struct ktbbhitl[2], 48 bytes @44

 struct kdbh, 14 bytes @100
    ub1 kdbhflag @100
    sb1 kdbhntab @101
    sb2 kdbhnrow @102
    sb2 kdbhfrre @104
    sb2 kdbhfsbo @106
    sb2 kdbhfseo @108
    sb2 kdbhavsp @110
    sb2 kdbhtosp @112

 struct kdbt[1], 4 bytes @114
    sb2 kdbtoffs @114
    sb2 kdbtnrow @116

 sb2 kdbr[3] @118

 ub1 freespace[8028] @124

 ub1 rowdata[36] @8152

 ub4 tailchk @8188

对比
-----MSSM
   struct ktbbhitl[2], 48 bytes            @44     

 struct kdbh, 14 bytes                     @92 

---ASSM  
   struct ktbbhitl[2], 48 bytes            @44     

 struct kdbh, 14 bytes                      @100
 
@92---->@100  kdbh偏移量发生了变化，增加了8个byte。