详解段头block和位图block每个offset的含义(非完整版)
本站文章除注明转载外，均为本站原创： 转载自love wife love life —Roger的Oracle/MySQL/PostgreSQL数据恢复博客
前几天跟lunar讨论问题，他提到关于数据库中段头block损坏的恢复以及假如出现位图block损坏等的情况恢复，
如何在没有备份的情况下，那就是个灾难，如果表小还好办，我们可以通过基于rowid等方式去扫描把数据抽取cats
出来，或者你可以使用odu/dul等数据抽取工具。 就像lunar提到的曾经遇到的一个case是有个表的段头坏了,但是
该表非常巨大，超过300g,在这种情况下，如果没有备份，处理起来就非常的麻烦了，虽然这样的情况很少见，但
我这里还是根据她的要求来研究下段头和位图block的结构，以便于我们在极端情况下用bbed等工具去直接修复.
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SQL> conn roger/roger Connected. SQL> select count(1) from t1; COUNT(1) ---------- 51042 SQL> col segment_name for a20 SQL> set lines 120 SQL> l 1 select owner,SEGMENT_NAME,HEADER_FILE,HEADER_BLOCK,blocks from dba_Segments 2* where owner='ROGER' and segment_name='T1' SQL> / OWNER SEGMENT_NAME HEADER_FILE HEADER_BLOCK BLOCKS ------------------------------ -------------------- ----------- ------------ ---------- ROGER T1 2 35 768 SQL> select name from v$datafile where file#=2; NAME ------------------------------------------------------------------- /home/ora10g/oradata/recover/roger01.dbf BBED> info File# Name Size(blks) ----- ---- ---------- 1 /home/ora10g/oradata/recover/system01.dbf 0 2 /home/ora10g/oradata/recover/roger01.dbf 0 3 /home/ora10g/oradata/recover/sysaux01.dbf 0 4 /home/ora10g/oradata/recover/users01.dbf 0 6 /home/ora10g/oradata/recover/undotbs2_01.dbf 0 8 /home/ora10g/oradata/recover/sqlt_01.dbf 0 BBED> set file 2 block 35 FILE# 2 BLOCK# 35 BBED> map /v File: /home/ora10g/oradata/recover/roger01.dbf (2) Block: 35 Dba:0x00800023 ------------------------------------------------------------ BBED-00400: invalid blocktype (35) |
该段头的dump信息如下：
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*** SESSION ID:(139.14) 2013-02-25 00:50:49.703 Start dump data blocks tsn: 6 file#: 2 minblk 35 maxblk 35 buffer tsn: 6 rdba: 0x00800023 (2/35) scn: 0x0000.005e08f2 seq: 0x01 flg: 0x04 tail: 0x08f22301 frmt: 0x02 chkval: 0x4715 type: 0x23=PAGETABLE SEGMENT HEADER Hex dump of block: st=0, typ_found=1 D0D9800 0000A223 00800023 005E08F2 04010000 [#...#.....^.....] D0D9810 00004715 00000000 00000000 00000000 [.G..............] D0D9820 00000000 00000015 00000300 00000A9C [................] D0D9830 00000014 00000051 00000080 0080065A [....Q.......Z...] D0D9840 00000000 00000014 00000000 000002D1 [................] D0D9850 00000000 00000000 00000000 00000014 [................] D0D9860 00000051 00000080 0080065A 00000000 [Q.......Z.......] D0D9870 00000014 00000000 000002D1 0080060A [................] D0D9880 0080060A 00000000 00000000 00000000 [................] D0D9890 00000000 00000000 00000000 00000000 [................] Repeat 3 times D0D98D0 00000001 00002000 00000000 00001434 [..... ......4...] D0D98E0 00000000 00800022 00000001 0080060A [...."...........] D0D98F0 00800022 00000000 00000000 00000000 ["...............] D0D9900 00000000 00000000 00000015 00000000 [................] D0D9910 0000E846 10000000 00800021 00000008 [F.......!.......] D0D9920 00800029 00000008 00800031 00000008 [).......1.......] D0D9930 00800039 00000008 00800041 00000008 [9.......A.......] D0D9940 00800049 00000008 00800051 00000008 [I.......Q.......] D0D9950 00800059 00000008 00800061 00000008 [Y.......a.......] D0D9960 00800069 00000008 00800071 00000008 [i.......q.......] D0D9970 00800079 00000008 00800081 00000008 [y...............] D0D9980 00800501 00000008 00800309 00000008 [................] D0D9990 00800311 00000008 00800389 00000080 [................] D0D99A0 00800409 00000080 00800509 00000080 [................] D0D99B0 00800589 00000080 00800609 00000080 [................] D0D99C0 00000000 00000000 00000000 00000000 [................] Repeat 142 times D0DA2B0 00800021 00800024 00800021 00800029 [!...$...!...)...] D0DA2C0 00800031 00800032 00800031 00800039 [1...2...1...9...] D0DA2D0 00800041 00800042 00800041 00800049 [A...B...A...I...] D0DA2E0 00800051 00800052 00800051 00800059 [Q...R...Q...Y...] D0DA2F0 00800061 00800062 00800061 00800069 [a...b...a...i...] D0DA300 00800071 00800072 00800071 00800079 [q...r...q...y...] D0DA310 00800081 00800082 00800081 00800501 [................] D0DA320 00800309 0080030A 00800309 00800311 [................] D0DA330 00800389 0080038B 00800409 0080040B [................] D0DA340 00800509 0080050B 00800589 0080058B [................] D0DA350 00800609 0080060B 00000000 00000000 [................] D0DA360 00000000 00000000 00000000 00000000 [................] Repeat 141 times D0DAC40 00000000 00000000 00800022 00000000 [........".......] D0DAC50 00000000 00000000 00000000 00000000 [................] Repeat 185 times D0DB7F0 00000000 00000000 00000000 08F22301 [.............#..] Extent Control Header ----------------------------------------------------------------- Extent Header:: spare1: 0 spare2: 0 #extents: 21 #blocks: 768 last map 0x00000000 #maps: 0 offset: 2716 Highwater:: 0x0080065a ext#: 20 blk#: 81 ext size: 128 #blocks in seg. hdr's freelists: 0 #blocks below: 721 mapblk 0x00000000 offset: 20 Unlocked -------------------------------------------------------- Low HighWater Mark : Highwater:: 0x0080065a ext#: 20 blk#: 81 ext size: 128 #blocks in seg. hdr's freelists: 0 #blocks below: 721 mapblk 0x00000000 offset: 20 Level 1 BMB for High HWM block: 0x0080060a Level 1 BMB for Low HWM block: 0x0080060a -------------------------------------------------------- Segment Type: 1 nl2: 1 blksz: 8192 fbsz: 0 L2 Array start offset: 0x00001434 First Level 3 BMB: 0x00000000 L2 Hint for inserts: 0x00800022 Last Level 1 BMB: 0x0080060a ---一级位图block dba Last Level II BMB: 0x00800022 ---二级位图block dba Last Level III BMB: 0x00000000 Map Header:: next 0x00000000 #extents: 21 obj#: 59462 flag: 0x10000000 Inc # 0 Extent Map ----------------------------------------------------------------- 0x00800021 length: 8 0x00800029 length: 8 0x00800031 length: 8 0x00800039 length: 8 0x00800041 length: 8 0x00800049 length: 8 0x00800051 length: 8 0x00800059 length: 8 0x00800061 length: 8 0x00800069 length: 8 0x00800071 length: 8 0x00800079 length: 8 0x00800081 length: 8 0x00800501 length: 8 0x00800309 length: 8 0x00800311 length: 8 0x00800389 length: 128 0x00800409 length: 128 0x00800509 length: 128 0x00800589 length: 128 0x00800609 length: 128 从这个extent map信息，可以得知该segment的大小为768个block. Auxillary Map -------------------------------------------------------- Extent 0 : L1 dba: 0x00800021 Data dba: 0x00800024 这里是位图block的map 列表，换句话讲，这里的block 也都是一级位图block。 Extent 1 : L1 dba: 0x00800021 Data dba: 0x00800029 第1个位图block 0x00800021对应的data block范围是:21~29 Extent 2 : L1 dba: 0x00800031 Data dba: 0x00800032 Extent 3 : L1 dba: 0x00800031 Data dba: 0x00800039 第2个位图block 0x00800031 对应的data block范围是:32~39 Extent 4 : L1 dba: 0x00800041 Data dba: 0x00800042 上面的length就是其extent的block个数. Extent 5 : L1 dba: 0x00800041 Data dba: 0x00800049 Extent 6 : L1 dba: 0x00800051 Data dba: 0x00800052 Extent 7 : L1 dba: 0x00800051 Data dba: 0x00800059 Extent 8 : L1 dba: 0x00800061 Data dba: 0x00800062 Extent 9 : L1 dba: 0x00800061 Data dba: 0x00800069 Extent 10 : L1 dba: 0x00800071 Data dba: 0x00800072 Extent 11 : L1 dba: 0x00800071 Data dba: 0x00800079 Extent 12 : L1 dba: 0x00800081 Data dba: 0x00800082 Extent 13 : L1 dba: 0x00800081 Data dba: 0x00800501 Extent 14 : L1 dba: 0x00800309 Data dba: 0x0080030a Extent 15 : L1 dba: 0x00800309 Data dba: 0x00800311 Extent 16 : L1 dba: 0x00800389 Data dba: 0x0080038b Extent 17 : L1 dba: 0x00800409 Data dba: 0x0080040b Extent 18 : L1 dba: 0x00800509 Data dba: 0x0080050b Extent 19 : L1 dba: 0x00800589 Data dba: 0x0080058b Extent 20 : L1 dba: 0x00800609 Data dba: 0x0080060b -------------------------------------------------------- Second Level Bitmap block DBAs -------------------------------------------------------- DBA 1: 0x00800022 End dump data blocks tsn: 6 file#: 2 minblk 35 maxblk 35 |
从上面我们可以看到，对于段头，里面的信息其实很简单，我们可以使用dbms包去转换dba地址为file、block号，如下：
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SQL> select dbms_utility.data_block_address_file(TO_NUMBER('80060a', 'XXXXXXXX')) file_id, dbms_utility.data_block_address_block(TO_NUMBER('80060a', 'XXXXXXXX')) block_id from dual; 2 FILE_ID BLOCK_ID ---------- ---------- 2 1546 SQL> select dbms_utility.data_block_address_file(TO_NUMBER('800022', 'XXXXXXXX')) file_id, 2 dbms_utility.data_block_address_block(TO_NUMBER('800022', 'XXXXXXXX')) block_id from dual; FILE_ID BLOCK_ID ---------- ---------- 2 34 SQL> |
如下是针对段头block的dump信息：
++++++++alter system dump datafile 2 block 35
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D0D9800 0000A223 00800023 005E08F2 04010000 [#...#.....^.....] D0D9810 00004715 00000000 00000000 00000000 [.G..............] D0D9820 00000000 00000015 00000300 00000A9C [................] D0D9830 00000014 00000051 00000080 0080065A [....Q.......Z...] D0D9840 00000000 00000014 00000000 000002D1 [................] D0D9850 00000000 00000000 00000000 00000014 [................] D0D9860 00000051 00000080 0080065A 00000000 [Q.......Z.......] D0D9870 00000014 00000000 000002D1 0080060A [................] D0D9880 0080060A 00000000 00000000 00000000 [................] D0D9890 00000000 00000000 00000000 00000000 [................] Repeat 3 times D0D98D0 00000001 00002000 00000000 00001434 [..... ......4...] D0D98E0 00000000 00800022 00000001 0080060A [...."...........] D0D98F0 00800022 00000000 00000000 00000000 ["...............] D0D9900 00000000 00000000 00000015 00000000 [................] D0D9910 0000E846 10000000 00800021 00000008 [F.......!.......] D0D9920 00800029 00000008 00800031 00000008 [).......1.......] D0D9930 00800039 00000008 00800041 00000008 [9.......A.......] D0D9940 00800049 00000008 00800051 00000008 [I.......Q.......] D0D9950 00800059 00000008 00800061 00000008 [Y.......a.......] D0D9960 00800069 00000008 00800071 00000008 [i.......q.......] D0D9970 00800079 00000008 00800081 00000008 [y...............] D0D9980 00800501 00000008 00800309 00000008 [................] D0D9990 00800311 00000008 00800389 00000080 [................] D0D99A0 00800409 00000080 00800509 00000080 [................] D0D99B0 00800589 00000080 00800609 00000080 [................] D0D99C0 00000000 00000000 00000000 00000000 [................] Repeat 142 times D0DA2B0 00800021 00800024 00800021 00800029 [!...$...!...)...] D0DA2C0 00800031 00800032 00800031 00800039 [1...2...1...9...] D0DA2D0 00800041 00800042 00800041 00800049 [A...B...A...I...] D0DA2E0 00800051 00800052 00800051 00800059 [Q...R...Q...Y...] D0DA2F0 00800061 00800062 00800061 00800069 [a...b...a...i...] D0DA300 00800071 00800072 00800071 00800079 [q...r...q...y...] D0DA310 00800081 00800082 00800081 00800501 [................] D0DA320 00800309 0080030A 00800309 00800311 [................] D0DA330 00800389 0080038B 00800409 0080040B [................] D0DA340 00800509 0080050B 00800589 0080058B [................] D0DA350 00800609 0080060B 00000000 00000000 [................] D0DA360 00000000 00000000 00000000 00000000 [................] Repeat 141 times D0DAC40 00000000 00000000 00800022 00000000 [........".......] D0DAC50 00000000 00000000 00000000 00000000 [................] Repeat 185 times D0DB7F0 00000000 00000000 00000000 08F22301 [.............#..] ---bbed dump file 2 block 35 BBED> d /v count 512 File: /home/ora10g/oradata/recover/roger01.dbf (2) Block: 35 Offsets: 0 to 511 Dba:0x00800023 ------------------------------------------------------- 23a20000 23008000 f2085e00 00000104 l #.#...^..... 15470000 00000000 00000000 00000000 l .G.............. 00000000 15000000 00030000 9c0a0000 l ................ 14000000 51000000 80000000 5a068000 l ....Q.......Z... 00000000 14000000 00000000 d1020000 l .............. 00000000 00000000 00000000 14000000 l ................ 51000000 80000000 5a068000 00000000 l Q.......Z....... 14000000 00000000 d1020000 0a068000 l .............. 0a068000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 01000000 00200000 00000000 34140000 l ..... ......4... 00000000 22008000 01000000 0a068000 l ...."........... 22008000 00000000 00000000 00000000 l "............... 00000000 00000000 15000000 00000000 l ................ 46e80000 00000010 21008000 08000000 l F.....!....... 29008000 08000000 31008000 08000000 l ).......1....... 39008000 08000000 41008000 08000000 l 9.......A....... 49008000 08000000 51008000 08000000 l I.......Q....... 59008000 08000000 61008000 08000000 l Y.......a....... 69008000 08000000 71008000 08000000 l i.......q....... 79008000 08000000 81008000 08000000 l y............... 01058000 08000000 09038000 08000000 l ................ 11038000 08000000 89038000 80000000 l ................ 09048000 80000000 09058000 80000000 l ................ 89058000 80000000 09068000 80000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ |
如下是段头block的每个offset的含义，这里我只是列举了大部分相对重要的offset：
offset 1: 23 表示block type 类型,23表示表段头,0x0b表示datafile header block类型.
offset 2: a2 表示block格式类型，这个跟普通的block格式类型一样。
offset 5~8: 23008000 表示该block的rdba地址，可以进行手工进行转换。
offset 9~14: f2085e00.0000 表示该block的scn值.
offset 15: 01 表示sequences号，是用于计算tail值用的.
offset 16: 04 表示flag值,针对block的flag值有如下几种属性：
#define KCBHFNEW 0x01 /* new block – zeroed data area */
#define KCBHFDLC 0x02 /* Delayed Logging Change advanced SCN/seq */
#define KCBHFCKV 0x04 /* ChecK Value saved – block xor’s to zero */
#define KCBHFTMP 0x08 /* Temporary block */
offset 17~18: 1547 表示block的check值，该值无所谓，如果用bbed进行修改后，可以sum apply会重新校验生成。
offset 37: 15 表示该段头信息所包含的extent个数，转换为10进制为21，即包含21个extent。
offset 41~42:0003,由于我这里字节序是32位，bbed看到的信息是反的，所以应该是0300,转换后为768，表示
这个段所包含的block个数，即段的大小,单位block
offset 45~46: 9c0a 表示extent header所在的offset，转换为10进制后为2716.
offset 49: 14 表示高水位标记的extent号.
offset 53：51 对于段头dump的blk#值，应该是值的block号
offset 57: 80 表示该extent所包含的block个数。 (offset 49~57 对应的都的高水位标记)
offset 60~64: 5a068000 表示表水位标记的rdba地址.
offset 69: 14 表示mapblk 对于的offset，居然含义不太清楚。
offset 76~80：d1020000 表示高水位标记下的blocks总数.
offset 92: 14 表示低水位标记的extent号.
offset 104~108: 5a068000 表示低水位标记的rdba地址.
offset 120~124: 5a068000 表示一级位图block的High HWM block rdba地址
offset 125~128: 5a068000 表示一级位图block的Low HWM block rdba地址
offset 213~214：2000 表示block size大小.
offset 221~224: 34140000 表示L2 Array start offset.
offset 229~232: 22008000 表示二级位图L2 Hint for inserts rdba地址.
offset 336~240: 0a068000 表示Last Level 1 BMB rdba地址。
offset 241~244：22008000 表示Last Level II BMB rdba地址.
offset 257~258: 46e8 表示object id号.
offset 261~264: 00000010 表示map header 的flag地址,段头的dump都是这个值.
offset 8189~8192：08F22301 表示该block的tail值。 该值属性为SCN bas+type+scn seq
中间还有一些Extent Map和Auxillary Map 信息,不多说了。
我想，了解上述的段头block的信息后，出现段头坏的情况，用bbed足以修复了。
接下来我们来看下位图block的结构，这里先说一级位图block.如下是一级位图block的dump信息：
+++++++ alter system dump datafile 2 block 1546
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Start dump data blocks tsn: 6 file#: 2 minblk 1546 maxblk 1546 buffer tsn: 6 rdba: 0x0080060a (2/1546) scn: 0x0000.005e08f0 seq: 0x02 flg: 0x04 tail: 0x08f02002 frmt: 0x02 chkval: 0x6a39 type: 0x20=FIRST LEVEL BITMAP BLOCK Hex dump of block: st=0, typ_found=1 Dump of memory from 0x0D0D9800 to 0x0D0DB800 D0D9800 0000A220 0080060A 005E08F0 04020000 [ .........^.....] D0D9810 00006A39 00000000 00000000 00000000 [9j..............] D0D9820 00000000 00000000 00000000 00000000 [................] Repeat 1 times D0D9840 00000000 00000000 00000000 00000004 [................] D0D9850 FFFFFFFF 0000002F 00000000 00000040 [..../.......@...] D0D9860 00010001 00000000 00000000 00000000 [................] D0D9870 00000000 00000011 00000000 00000000 [................] D0D9880 00000000 00000000 00000000 00000000 [................] D0D9890 00800022 00000011 00000014 00000051 ["...........Q...] D0D98A0 00000080 0080065A 00000000 00000014 [....Z...........] D0D98B0 00000000 000002D1 00000000 00000001 [................] D0D98C0 0000E846 00000000 00000000 00800649 [F...........I...] D0D98D0 00000040 00000000 00000000 00000000 [@...............] D0D98E0 00000000 00000000 00000000 00000000 [................] Repeat 9 times D0D9980 00000000 00000000 00000000 11111111 [................] D0D9990 11111111 00000010 00000000 00000000 [................] D0D99A0 00000000 00000000 00000000 00000000 [................] Repeat 484 times D0DB7F0 00000000 00000000 00000000 08F02002 [............. ..] Dump of First Level Bitmap Block -------------------------------- nbits : 4 nranges: 1 parent dba: 0x00800022 poffset: 17 unformatted: 47 total: 64 first useful block: 0 owning instance : 1 instance ownership changed at Last successful Search Freeness Status: nf1 0 nf2 0 nf3 0 nf4 0 Extent Map Block Offset: 4294967295 First free datablock : 17 Bitmap block lock opcode 0 Locker xid: : 0x0000.000.00000000 Inc #: 0 Objd: 59462 HWM Flag: HWM Set Highwater:: 0x0080065a ext#: 20 blk#: 81 ext size: 128 #blocks in seg. hdr's freelists: 0 #blocks below: 721 mapblk 0x00000000 offset: 20 -------------------------------------------------------- DBA Ranges : -------------------------------------------------------- 0x00800649 Length: 64 Offset: 0 0:FULL 1:FULL 2:FULL 3:FULL 4:FULL 5:FULL 6:FULL 7:FULL 8:FULL 9:FULL 10:FULL 11:FULL 12:FULL 13:FULL 14:FULL 15:FULL 16:FULL 17:unformatted 18:unformatted 19:unformatted 20:unformatted 21:unformatted 22:unformatted 23:unformatted 24:unformatted 25:unformatted 26:unformatted 27:unformatted 28:unformatted 29:unformatted 30:unformatted 31:unformatted 32:unformatted 33:unformatted 34:unformatted 35:unformatted 36:unformatted 37:unformatted 38:unformatted 39:unformatted 40:unformatted 41:unformatted 42:unformatted 43:unformatted 44:unformatted 45:unformatted 46:unformatted 47:unformatted 48:unformatted 49:unformatted 50:unformatted 51:unformatted 52:unformatted 53:unformatted 54:unformatted 55:unformatted 56:unformatted 57:unformatted 58:unformatted 59:unformatted 60:unformatted 61:unformatted 62:unformatted 63:unformatted -------------------------------------------------------- End dump data blocks tsn: 6 file#: 2 minblk 1546 maxblk 1546 ----bbed dump BBED> set file 2 block 1546 FILE# 2 BLOCK# 1546 BBED> d /v count 512 File: /home/ora10g/oradata/recover/roger01.dbf (2) Block: 1546 Offsets: 0 to 511 Dba:0x0080060a ------------------------------------------------------- 20a20000 0a068000 f0085e00 00000204 l .....^..... 396a0000 00000000 00000000 00000000 l 9j.............. 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 04000000 l ................ ffffffff 2f000000 00000000 40000000 l ..../.......@... 01000100 00000000 00000000 00000000 l ................ 00000000 11000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 22008000 11000000 14000000 51000000 l "...........Q... 80000000 5a068000 00000000 14000000 l ....Z........... 00000000 d1020000 00000000 01000000 l .............. 46e80000 00000000 00000000 49068000 l F.........I... 40000000 00000000 00000000 00000000 l @............... 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 11111111 l ................ 11111111 10000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ 00000000 00000000 00000000 00000000 l ................ <16 bytes per line> |
offset 1: 20 表示block type类型，20表示一级位图block，21表示二级位图block，22表示三级位图block。
offset 2：a2 表示block格式类型，这个跟普通的block格式类型一样
offset 5~8: 0a068000 表示该block的rdba地址.
offset 9~12: f0085e00 表示scn值.
offset 15: 02 表示sequence值
offset 16: 04 表示flag值.
offset 17~20: 396a0000 表示block 的check 值.
offset 81~84: ffffffff 表示Extent Map Block Offset值,这里该位图block没有extent map，所以默认为最大值也就是8个f.
offset 85: 2f 表示unformatted block的个数. 即高水位上的block个数。
offset 92: 40 表示该位图block所对应的data block个数.
offset 117: 11 表示该位图block所对应的parent dba的offset值.
offset 145~148: 22008000 表示该位图block的parent block dba地址。
offset 165~168：5a068000 表示Highwater 标记dba地址.
offset 181~184: d1020000 表示高水位标记下的block总数.
offset 193~196: 46e80000 表示object id号.
offset 205~208:49068000 表示该位图block所对应的数据块dba ranges地址的起始值。
最后我们来看下二级位图block的结构：
Start dump data blocks tsn: 6 file#: 2 minblk 34 maxblk 34
buffer tsn: 6 rdba: 0x00800022 (2/34)
scn: 0x0000.0061c551 seq: 0x03 flg: 0x04 tail: 0xc5512103
frmt: 0x02 chkval: 0x6c9d type: 0x21=SECOND LEVEL BITMAP BLOCK
Hex dump of block: st=0, typ_found=1
Dump of memory from 0x0D0D9800 to 0x0D0DB800
D0D9800 0000A221 00800022 0061C551 04030000 [!…”…Q.a…..]
D0D9810 00006C9D 00000000 00000000 00000000 [.l…………..]
D0D9820 00000000 00000000 00000000 00000000 […………….]
Repeat 1 times
D0D9840 00000000 00000000 00000000 00800023 […………#…]
D0D9850 00000064 00000001 00000062 00000000 [d…….b…….]
D0D9860 00000000 00000000 0000E846 00000001 [……..F…….]
D0D9870 00000000 00800021 00010001 00800031 [….!…….1…]
……..
D0D9B90 00010001 00000000 00000000 00000000 […………….]
D0D9BA0 00000000 00000000 00000000 00000000 […………….]
Repeat 452 times
D0DB7F0 00000000 00000000 00000000 C5512103 [………….!Q.]
Dump of Second Level Bitmap Block
number: 100 nfree: 1 ffree: 98 pdba: 0x00800023
Inc #: 0 Objd: 59462
opcode:0
xid:
L1 Ranges :
——————————————————–
0x00800021 Free: 1 Inst: 1
0x00800031 Free: 1 Inst: 1
0x00800041 Free: 1 Inst: 1
0x00800051 Free: 1 Inst: 1
………
可以看到，二级位图block的结构也不复杂，除了头部的信息跟前面的一级位图block基本上一致外，后面就是一个
对应的一级位图block的dba 范围列表。所以这里我就不再相信去描述二级位图block的每个offset的具体含义了。
同理，三级位图block的结构也是类似的，不同的是除开前面的头部信息外，后面跟着的是对应的二级位图block的范围列表信息。
事实上，对于8k的block size，要出现三级位图block是非常困难的，一般情况下大家根本遇不到的。
最后简单总结下：
1. 针对段头损坏的情况，如果有备份，可以使用rman的blockrecover，如果没有备份，那么就很悲剧了。
2. 如果位图block损坏，即使没有备份，也可以使用基于rowid的方式进行cats抽取数据。
3. 针对上面的2种情况，都可以使用odu、dul等工具抽取数据。
4. 如果问题不复杂的话，在备份数据文件后，你可以使用bbed去修复上面的块损坏，不过这个要慎重。
5. 我这里是32位，bbed dump是反的，另外我是从offset 1开始(图方便计算)，大家自己算的时候减1个offset即可.
6. 本来不计划发出来的，想想还是发出来，免得大家说我藏着掖着，但是注意，出问题了，我概不负责哦！！！
最后是贴个模拟段头损坏的情况：
|
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Mon Feb 25 07:00:24 PST 2013 Hex dump of (file 2, block 35) in trace file /home/ora10g/admin/recover/bdump/recover_j000_5559.trc Corrupt block relative dba: 0x00800023 (file 2, block 35) Bad header found during buffer read Data in bad block: type: 85 format: 5 rdba: 0x00888823 last change scn: 0x0000.0061c639 seq: 0x1 flg: 0x04 spare1: 0x0 spare2: 0x0 spare3: 0x0 consistency value in tail: 0xc6392301 check value in block header: 0x8778 computed block checksum: 0xab89 Reread of rdba: 0x00800023 (file 2, block 35) found same corrupted data Mon Feb 25 07:00:24 PST 2013 Corrupt Block Found TSN = 6, TSNAME = ROGER RFN = 2, BLK = 35, RDBA = 8388643 OBJN = 59462, OBJD = 59462, OBJECT = T1, SUBOBJECT = SEGMENT OWNER = ROGER, SEGMENT TYPE = Table Segment Mon Feb 25 07:00:24 PST 2013 |
使用使用bbed修改block前面的部分即可，dba地址我们可以转换进行反推，如下：
|
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SQL> select dbms_utility.data_block_address_file(TO_NUMBER('800023', 'XXXXXXXX')) file_id, dbms_utility.data_block_address_block(TO_NUMBER('800023', 'XXXXXXXX')) block_id from dual; 2 FILE_ID BLOCK_ID ---------- ---------- 2 35 SQL> SQL> select count(1) from roger.t1; COUNT(1) ---------- 432330 |
5 Responses to “详解段头block和位图block每个offset的含义(非完整版)”
[…] 详见原文博客链接第：详解段头block和位图block每个offset的… 作者：lovewifelovelife 发表于2013-2-28 20:46:55 原文链接 阅读：25 评论：0 查看评论 […]
顶roger,加油,精辟而独到.学习
请教一下，基于rowid等方式去扫描把数据抽取cats
出来 ，是怎么做的。
找出是哪个块损坏了，这个块rowid排除出去:例如这个块有rowid10、rowid11、rowid12，可以create table t1 as select * from tab where rowidrowid12;
这样来做！
奇怪了 打空格 怎么变成=“”了！
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