BMB结构问题探讨

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最新推荐文章于 2025-07-22 15:31:01 发布

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文章标签：数据库

本文探讨了 Oracle 数据库中 BMB（Bit Map Block）结构的组织方式，具体分析了 FIRST LEVEL BITMAP BLOCK、SECOND LEVEL BITMAP BLOCK 和 PAGE TABLE SEGMENT HEADER 的关系，并通过实例展示了这些结构是如何存储和管理数据块的。

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LINUX AS 4 2.6.9
ORACLE 9.2.0.4

SQL> select file_id,block_id,blocks from dba_extents where segment_name='I_TEST' and owner='DBLU';

FILE_ID BLOCK_ID BLOCKS
---------- ---------- ----------
16 2609769 8

问个BMB结构问题，为什么是这样的顺序：FIRST LEVEL BITMAP BLOCK->SECOND LEVEL BITMAP BLOCK->PAGETABLE SEGMENT HEADER,
而不是PAGETABLE SEGMENT HEADER->SECOND LEVEL BITMAP BLOCK->FIRST LEVEL BITMAP以下是跟踪文件：

*** SESSION ID

55.24913) 2010-08-24 17:06:46.714
Start dump data blocks tsn: 15 file#: 16 minblk 2609769 maxblk 2609769buffer tsn: 15 rdba: 0x0427d269 (16/2609769)
scn: 0x0023.593588a2 seq: 0x02 flg: 0x00 tail: 0x88a22002
frmt: 0x02 chkval: 0x0000 type: 0x20=FIRST LEVEL BITMAP BLOCK
Dump of First Level Bitmap Block
--------------------------------
nbits : 2 nranges: 1       parent dba:  0x0427d26a poffset: 0
unformatted: 0    total: 8       first useful block: 3
owning instance : 1
instance ownership changed at 08/24/2010 17:00:28
Last successful Search 08/24/2010 17:00:28
Freeness Status:  nf1 0    nf2 2    nf3 0    nf4 0

Extent Map Block Offset: 4294967295
First free datablock : 4
Bitmap block lock opcode 0
Locker xid:    :  0x0000.000.00000000
   Highwater::  0x0427d271  ext#: 0    blk#: 8    ext size: 8
  #blocks in seg. hdr's freelists: 0
  #blocks below: 5
  mapblk  0x00000000  offset: 0
  HWM Flag: HWM Set
  --------------------------------------------------------
  DBA Ranges :
  --------------------------------------------------------
0x0427d269  Length: 8    Offset: 0

0:Metadata 1:Metadata 2:Metadata 3:FULL
4:25-50% free 5:FULL 6:FULL 7:25-50% free
  --------------------------------------------------------
End dump data blocks tsn: 15 file#: 16 minblk 2609769 maxblk 2609769
Start dump data blocks tsn: 15 file#: 16 minblk 2609770 maxblk 2609770
buffer tsn: 15 rdba: 0x0427d26a (16/2609770)
scn: 0x0023.593588a0 seq: 0x01 flg: 0x00 tail: 0x88a02101
frmt: 0x02 chkval: 0x0000 type: 0x21=SECOND LEVEL BITMAP BLOCK
Dump of Second Level Bitmap Block
number: 1    nfree: 1    ffree: 0    pdba:    0x0427d26b
  opcode:0
xid:
  L1 Ranges :
  --------------------------------------------------------
0x0427d269  Free: 3 Inst: 1

  --------------------------------------------------------
End dump data blocks tsn: 15 file#: 16 minblk 2609770 maxblk 2609770
Start dump data blocks tsn: 15 file#: 16 minblk 2609771 maxblk 2609771
buffer tsn: 15 rdba: 0x0427d26b (16/2609771)
scn: 0x0023.593588a0 seq: 0x02 flg: 0x00 tail: 0x88a02302
frmt: 0x02 chkval: 0x0000 type: 0x23=PAGETABLE SEGMENT HEADER
  Extent Control Header
  -----------------------------------------------------------------
  Extent Header:: spare1: 0    spare2: 0    #extents: 1    #blocks: 8
               last map  0x00000000  #maps: 0    offset: 2716
   Highwater::  0x0427d271  ext#: 0    blk#: 8    ext size: 8
  #blocks in seg. hdr's freelists: 0
  #blocks below: 5
  mapblk  0x00000000  offset: 0
               Unlocked
  --------------------------------------------------------
  Low HighWater Mark :
   Highwater::  0x0427d271  ext#: 0    blk#: 8    ext size: 8

[ 本帖最后由 microsoft_fly 于 2010-8-24 17:28 编辑 ]

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