back segment 或 undo tablespace
--- Itl itl 的序号
--- xid: 8 bytes 值可以用select XIDUSN, XIDSLOT,XIDSQN from v$transaction;查到
--- This is comprised of the rollback segment number (2 bytes), the slot number
--- in the transaction table of that rollback segment (2 bytes), and the number
--- of times use of that transaction table has wrapped (4 bytes).
--- Uba: 8 bytes The location of the undo for the most recent change to this block by this
--- transaction. This is comprised of the DBA of the rollback segment block (4
--- bytes), the sequence number (2 bytes), and the record number for the change
--- in that undo block (1 byte), plus 1 unused byte.
--- flag 1 nibble ---- = transaction is active, or committed pending cleanout
--- C--- = transaction has been committed and locks cleaned out
--- -B-- = this undo record contains the undo for this ITL entry
--- --U- = transaction committed (maybe long ago); SCN is an upper bound
--- ---T = transaction was still active at block cleanout SCN
--- Lck 3 nibbles The number of row-level locks held in the block by this transaction.
--- Scn/Fsc 6 bytes If the transaction has been cleaned out, this is the commit SCN or an upper
--- bound thereof. Otherwise the leading two bytes contain the free space credit
--- for the transaction - that is, the number of bytes freed in the block by the
--- transaction
--- 参考http://www.ixora.com.au/q+a/datablock.htm#end
---
----------------------- 第四部分
data_block_dump
===============
tsiz: 0x1fb8
hsiz: 0x14
pbl: 0x02476c44
bdba: 0x01000003
flag=-----------
ntab=1
nrow=1
frre=-1
fsbo=0x14
fseo=0x1fb2
avsp=0x1f9b
tosp=0x1f9b
0xe:pti[0] nrow=1 offs=0
0x12:pri[0] offs=0x1fb2
--- tsiz: hsiz: pbl: bdba: 在数据文件都是没有存储的
--- tsiz: 除了上面的3部分和block尾部的4个字节剩下的空间 0x1fb8就是8120字节 8k的block:
--- 8192-20(block head)-24(Transaction Header)-24(一个事务条)-4(block tail)=8120
--- hsiz: 数据块头20个字节+数据块尾4个字节=24字节(0x14)
--- pbl: ptr to buffer holding the block 我是用的专用模式dump的datafile中的block出来
--- 在同一个session的dump文件中 dump 出来的block 的这个都是同一个值
--- bdba: 和第一部分中的rdba 一个意思
--- flag 1 byte N=pctfree hit(clusters), F=don''''t put on free list
--- K=flushable cluster keys. 当然还有别的标记: A ...
--- ntab 1 byte 这block中有几个table的数据 cluster这个就可能大于1
--- nrow 2 bytes block 中有多少行数据
--- frre 2 bytes First free row index entry. -1=you have to add one.
--- fsbo 2 bytes Free Space Begin offset
--- fseo 2 bytes Free Space End offset
--- avsp 2 bytes Available space in the block <pctfree and pctused?>
--- tosp 2 bytes Total available space when all TXs commit
--- 0xe: nrow 2 bytes block 中的这个table有多少行数据
--- 0xe: offs 2 bytes 偏移量 用 cluster 的时候可以看出值
----------------------- 第五部分
block_row_dump:
tab 0, row 0, @0x1fb2
tl: 6 fb: --H-FL-- lb: 0x1 cc: 1
col 0: [ 2] c1 02
end_of_block_dump
--- tl: 这条记录中的长度 包括row head 的一般情况的 3 字节和表示数据长度的1字节和数据本身的长度
--- fb: 1 byte K = Cluster Key (Flags may change meaning if this is set to show HASH cluster)
--- C = Cluster table member
--- H = Head piece of row
--- D = Deleted row
--- F = First data piece
--- L = Last data piece
--- P = First column continues from previous piece
--- N = Last column continues in next piece
--- lb: 1 byte 和上面第三部分的 ITL 的lck相对应 表示这行是否被 lock 了
--- cc: 1 byte 表示这行有几列数据
--- col 0: [ 2] : 1 byte 表示这行的这列的长度
--- c1 02 : 这就是table中的数据 "1" 可以通过下面的语句看 oracle真正使用的是
--- 那些16进制的数据来表示的用户数据 select dump(col_name,16) from table_name;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
下面的数据就是上面的 dump 文件对应的2进制文件 我依照 2 进制数据的顺序解释内容
------------------------ 下面的对应上面dump 文件的第一部分
Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F
00006000 06 02 00 00 03 00 00 01 A5 02 08 00 00 00 01 02
00006010 00 00 00 00
--- 06 : type: 0x06=trans data (对应上面dump文件中的内容)
--- 02 : frmt: 0x02
--- 00 00 : filler 应该是 unused 上面的dump文件中并没有显示这部分内容
--- 03 00 00 01 : rdba: 0x01000003 在同一个 tablespace 中是唯一的 当 datafile 中可能不唯一
--- 来看看他的规律 :连续建4个 datafile 他们的第一block为
--- 0x 01 00 04 01
--- 0x 01 00 08 01
--- 0x 01 00 0c 01
--- 0x 01 00 00 02
--- 对应的数据在是 0x01040001 , 0x01080001 , 0x010c0001 , 0x02000001
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