墨墨导读:的全过程。 墨天轮主页:https://www./u/6722 Oracle中delete行时,数据实际上并没有被删除。而是将行标记为已删除,并相应地调整空闲空间计数器和指针。行状态存储在每行的行标头中,该行标头占用每行的前几个字节。 行标头由行标记、锁字节(ITL条目)和列计数组成。第一个Row标志是一个单字节,它保存一个显示行状态的位掩码。位掩码解码如下 当数据被删除后,行标头+16即60=>0x3c 测试:1,创建测试数据SQL> create table devin.test_delete(id number,name nvarchar2(10)) tablespace devin; 可以看到表位于9号文件,段头块是138,先dump 138快,根据段头找到具体的数据存放的block。 2,dump header blockSQL> alter system dump datafile 9 block 138;
System altered.
*** 2021-02-05T11:00:07.663087+08:00 Start dump data blocks tsn: 9 file#:9 minblk 138 maxblk 138 Block dump from cache: Dump of buffer cache at level 4 for pdb=0 tsn=9 rdba=37748874 BH (0x6ebdb498) file#: 9 rdba: 0x0240008a (9/138) class: 4 ba: 0x6e8da000 set: 6 pool: 3 bsz: 8192 bsi: 0 sflg: 0 pwc: 0,0 dbwrid: 0 obj: 75550 objn: 75550 tsn: [0/9] afn: 9 hint: f hash: [0x694952d8,0x694952d8] lru: [0x6efe92d8,0x6dffa478] ckptq: [NULL] fileq: [NULL] objq: [0x6dffa4a0,0x6d3d98c0] objaq: [0x62810c10,0x6dffa4b0] st: XCURRENT md: NULL fpin: 'ktswh03: ktscts' fscn: 0x2374fe0 tch: 3 flags: block_written_once LRBA: [0x0.0.0] LSCN: [0x0] HSCN: [0x2374ff7] HSUB: [3] Printing buffer operation history (latest change first): cnt: 12 01. sid:09 L192:kcbbic2:bic:FBD 02. sid:09 L191:kcbbic2:bic:FBW 03. sid:09 L602:bic1_int:bis:FWC 04. sid:09 L822:bic1_int:ent:rtn 05. sid:09 L832:oswmqbg1:clr:WRT 06. sid:09 L930:kubc:sw:mq 07. sid:09 L913:bxsv:sw:objq 08. sid:09 L608:bxsv:bis:FBW 09. sid:09 L607:bxsv:bis:FFW 10. sid:07 L464:chg1_mn:bic:FMS 11. sid:07 L778:chg1_mn:bis:FMS 12. sid:07 L353:gcur:set:MEXCL 13. sid:07 L464:chg1_mn:bic:FMS 14. sid:07 L778:chg1_mn:bis:FMS 15. sid:07 L353:gcur:set:MEXCL 16. sid:07 L464:chg1_mn:bic:FMS Block dump from disk: buffer tsn: 9 rdba: 0x0240008a (9/138) scn: 0x2374ff7 seq: 0x03 flg: 0x04 tail: 0x4ff72303 frmt: 0x02 chkval: 0x8ea3 type: 0x23=PAGETABLE SEGMENT HEADER Hex dump of block: st=0, typ_found=1 Dump of memory from 0x00007FC4D3834000 to 0x00007FC4D3836000 7FC4D3834000 0000A223 0240008A 02374FF7 04030000 [#.....@..O7.....] 7FC4D3834010 00008EA3 00000000 00000000 00000000 [................] 7FC4D3834020 00000000 00000001 00000008 00000A9C [................] 7FC4D3834030 00000000 00000008 00000008 02400090 [..............@.] 7FC4D3834040 00000000 00000000 00000000 00000005 [................] 7FC4D3834050 00000000 00000000 00000000 00000000 [................] 7FC4D3834060 00000008 00000008 02400090 00000000 [..........@.....] 7FC4D3834070 00000000 00000000 00000005 02400088 [..............@.] 7FC4D3834080 02400088 00000000 00000000 00000000 [..@.............] 7FC4D3834090 00000000 00000000 00000000 00000000 [................] Repeat 3 times 7FC4D38340D0 00000001 00002000 00000000 00001434 [..... ......4...] 7FC4D38340E0 00000000 02400089 00000001 02400088 [......@.......@.] 7FC4D38340F0 02400089 00000000 00000000 00000000 [..@.............] 7FC4D3834100 00000000 00000000 00000001 00000000 [................] 7FC4D3834110 0001271E 10000000 02400088 00000008 [.'........@.....] 7FC4D3834120 00000000 00000000 00000000 00000000 [................] Repeat 152 times 7FC4D3834AB0 02400088 0240008B 00000000 00000000 [..@...@.........] 7FC4D3834AC0 00000000 00000000 00000000 00000000 [................] Repeat 151 times 7FC4D3835440 00000000 00000000 02400089 00000000 [..........@.....] 7FC4D3835450 00000000 00000000 00000000 00000000 [................] Repeat 185 times 7FC4D3835FF0 00000000 00000000 00000000 4FF72303 [.............#.O] Extent Control Header ----------------------------------------------------------------- Extent Header:: spare1: 0 spare2: 0 #extents: 1 #blocks: 8 last map 0x00000000 #maps: 0 offset: 2716 Highwater:: 0x02400090 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:: 0x02400090 ext#: 0 blk#: 8 ext size: 8 #blocks in seg. hdr's freelists: 0 #blocks below: 5 mapblk 0x00000000 offset: 0 Level 1 BMB for High HWM block: 0x02400088 Level 1 BMB for Low HWM block: 0x02400088 -------------------------------------------------------- Segment Type: 1 nl2: 1 blksz: 8192 fbsz: 0 L2 Array start offset: 0x00001434 First Level 3 BMB: 0x00000000 L2 Hint for inserts: 0x02400089 Last Level 1 BMB: 0x02400088 Last Level II BMB: 0x02400089 Last Level III BMB: 0x00000000 Map Header:: next 0x00000000 #extents: 1 obj#: 75550 flag: 0x10000000 Inc # 0 Extent Map ----------------------------------------------------------------- 0x02400088 length: 8 Auxillary Map -------------------------------------------------------- Extent 0 : L1 dba: 0x02400088 Data dba: 0x0240008b -------------------------------------------------------- Second Level Bitmap block DBAs -------------------------------------------------------- DBA 1: 0x02400089 End dump data blocks tsn: 9 file#: 9 minblk 138 maxblk 138
--可以看到DATA DBA : 0x0240008b
SQL> select getbfno('0x0240008b') from dual;
GETBFNO('0X0240008B') ---------------------------------------------------- datafile# is:9 datablock is:139 dump command:alter system dump datafile 9 block 139;
--即数据存储从block 139开始 3,查找被删除的数据BBED> set dba 9,139 4,修改行标头BBED> m /x 2c offset 8149 5,验证SQL> alter system flush buffer_cache; 数据成功恢复。 作者 肖杰:云和恩墨Oracle技术顾问,长期服务于银行,金融,能源等行业的数据中心,8年数据库运维经验,擅长Oracle,PostgreSQL等数据库高可用设计和运维故障处理,异常恢复,升级迁移,性能优化。 墨天轮原文链接:https://www./db/44829(复制到浏览器中打开或者点击“阅读原文”立即查看) |
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