之前在Data Block Structure (Try to Understand)中通过dump文件来尝试去分析一个block的结构，结果费了半天劲，也没有得到一个很清晰的概念。发现BBED的map命令很好很强大，可以用来得到一个block的结构组织情况，
通过设置dba来得到一个block的结构，如下所示...
BBED> map /v dba 6, 12
File: /u01/app/oracle/oradata/orcl/small_tbs01.dbf (6)
Block: 12 Dba:0x0180000c
------------------------------------------------------------
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
b2 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
b1 kdbhntab @101
b2 kdbhnrow @102
sb2 kdbhfrre @104
sb2 kdbhfsbo @106
sb2 kdbhfseo @108
b2 kdbhavsp @110
b2 kdbhtosp @112
struct kdbt[1], 4 bytes @114
b2 kdbtoffs @114
b2 kdbtnrow @116
sb2 kdbr[1] @118
ub1 freespace[8056] @120
ub1 rowdata[12] @8176
ub4 tailchk @8188
BBED>
这里面的一系列的struct，可以参见如下介绍...
////////////////////////////////////////////////////////////////////////////////////////
//////////// Block Header Structure, 20 bytes//////////////////////////////////////////
struct kcbh, 20 bytes @0
ub1 type_kcbh @0 -- Block Type
-- 01 - Undo segment header
-- 02 - Undo data block
-- 03 - Save undo header
-- 04 - Save undo data block
-- 05 - Data segment header
-- 06 - Trans data, KTB managed data block(with ITL)
-- 07 - Temp table data block (no ITL)
-- 08 - Sort key
-- 09 - Sort Run
-- 10 - Segment free list block
-- 11 - Data file header
ub1 frmt_kcbh @1 -- Block Format 1=Oracle7, 2=Oracle8+
ub1 spare1_kcbh @2 -- Not used, filler field
ub1 spare2_kcbh @3 -- Not used, filler field
ub4 rdba_kcbh @4 -- RDBA (4 bytes) - Relative Data Block Address
ub4 bas_kcbh @8 -- SCN Base (4 bytes)
ub2 wrp_kcbh @12 -- SCN Wrap (2 bytes)
ub1 seq_kcbh @14 -- Sequence Number, incremented for every change made to the block at the same SCN
ub1 flg_kcbh @15 -- Flag:
-- 0x01 New Block
-- 0x02 Delayed Logging Chang advanced SCN/seq
-- 0x04 Check value saved - block XOR's to Zero
-- 0x08 Temporary block
ub2 chkval_kcbh @16 -- Optional block checksum (if DB_BLOCK_CHECKSUM=TRUE)
ub2 spare3_kcbh @18 -- Not used, filler field
/////////////////////////////////////////////////////////////////////////////////////////
/////////Transaction Fixed Header Structure, 72 Bytes////////////////////////////////////
struct ktbbh, 72 bytes @20
ub1 ktbbhtyp @20 -- Block type (1=DATA, 2=INDEX)
union ktbbhsid, 4 bytes @24 -- Segment/Object ID
struct ktbbhcsc, 8 bytes @28 -- SCN at last block cleanout
b2 ktbbhict @36 -- Number of ITL slots
ub1 ktbbhflg @38 -- 0=on the freelist
ub1 ktbbhfsl @39 -- ITL TX freelist slot
ub4 ktbbhfnx @40 -- DBA of next block on the freelist
struct ktbbhitl[2], 48 bytes @44 -- ITL list index, each ITL takes up 24 bytes
//////////////////////////////////////////////////////////////////////////////////////////
///////////////Data Header Structure, 14 bytes////////////////////////////////////////////
struct kdbh, 14 bytes @100
ub1 kdbhflag @100 -- N=pctfree hit(clusters)
-- F=do not put on freelist
-- K=flushable cluster keys
b1 kdbhntab @101 -- Number of tables (>1 in clusters)
b2 kdbhnrow @102 -- Number of rows (2 bytes)
sb2 kdbhfrre @104 -- First free row entry index; -1=you have to add one
sb2 kdbhfsbo @106 -- Freespace begin offset
sb2 kdbhfseo @108 -- Freespace end offset
b2 kdbhavsp @110 -- Available space in the block
b2 kdbhtosp @112 -- Total available space when all TXs commit
////////////////////////////////////////////////////////////////////////////////////////
/////////////////////Table Directory Entry Structure, 4 bytes///////////////////////////
struct kdbt[1], 4 bytes @114
b2 kdbtoffs @114
b2 kdbtnrow @116
////////////////////////////////////////////////////////////////////////////////////////
////////////////// Row Directory ///////////////////////////////////////////////////////
sb2 kdbr[1] @118
////////////////////////////////////////////////////////////////////////////////////////
///////////////// Free Space ///////////////////////////////////////////////////////////
ub1 freespace[8056] @120
///////////////////////////////////////////////////////////////////////////////////////
/////////////////////Row Data//////////////////////////////////////////////////////////
ub1 rowdata[12] @8176
//////////////////////////////////////////////////////////////////////////////////////
/////////////////////Block Tail Check, 4 bytes////////////////////////////////////////
ub4 tailchk @8188 -- Lower order two bytes of SCN Base + Block Type + SCN Seq
