通过rowid获取segment header坏块数据

在上篇(table中各种坏块对select/dml操作影响)中说到如果segment header异常了，不能通过ctas来获得相关数据，在群的讨论中，EZIO说到可以通过rowid方式来获得相关数据，通过测试证明，确实可以通过该方法获得数据，以后遇到此类错误，大家也不必惊慌.
创建测试表

SQL> create table t_xifenfei
  2  as
  3  select * from dba_objects where object_id is not null;


SQL> alter table t_xifenfei
  2  add constraint PK_t_xifenfei primary key (object_id)
  3  ;

Table altered.

SQL> alter system checkpoint;

System altered.

SQL> select count(*) from chf.t_xifenfei;

  COUNT(*)
----------
     74762

SQL> select header_file,header_block from 
  2  DBA_SEGments where segment_name='T_XIFENFEI' AND OWNER='CHF';

HEADER_FILE HEADER_BLOCK
----------- ------------
          4          170

dump block

alter system dump datafile 4 block 170;

Dump of buffer cache at level 4 for tsn=4 rdba=16777386
Block dump from disk:
buffer tsn: 4 rdba: 0x010000aa (4/170)
scn: 0x0b8c.3c0092e4 seq: 0x01 flg: 0x04 tail: 0x91e42301
frmt: 0x02 chkval: 0xa531 type: 0x23=PAGETABLE SEGMENT HEADER

通过header_block和dump block确定block 170即为PAGETABLE SEGMENT HEADER

bbed制造SEGMENT HEADER坏块

BBED> set block 170
        BLOCK#          170

BBED> set offset 8188
        OFFSET          8188

BBED> d
 File: /u01/oracle/oradata/ora11g/users01.dbf (0)
 Block: 170              Offsets: 8188 to 8191           Dba:0x00000000
------------------------------------------------------------------------
 0123e492 

 <32 bytes per line>

BBED> m /x 0123e491
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
 File: /u01/oracle/oradata/ora11g/users01.dbf (0)
 Block: 170              Offsets: 8188 to 8191           Dba:0x00000000
------------------------------------------------------------------------
 0123e491 

 <32 bytes per line>

BBED> sum apply 
Check value for File 0, Block 170:
current = 0xa531, required = 0xa531

BBED> verify
DBVERIFY - Verification starting
FILE = /u01/oracle/oradata/ora11g/users01.dbf
BLOCK = 170

Block 170 is corrupt
Corrupt block relative dba: 0x010000aa (file 0, block 170)
Fractured block found during verification
Data in bad block:
 type: 35 format: 2 rdba: 0x010000aa
 last change scn: 0x0b8c.3c0092e4 seq: 0x1 flg: 0x04
 spare1: 0x0 spare2: 0x0 spare3: 0x0
 consistency value in tail: 0x91e42301
 check value in block header: 0xa531
 computed block checksum: 0x0


DBVERIFY - Verification complete

Total Blocks Examined         : 1
Total Blocks Processed (Data) : 0
Total Blocks Failing   (Data) : 0
Total Blocks Processed (Index): 0
Total Blocks Failing   (Index): 0
Total Blocks Empty            : 0
Total Blocks Marked Corrupt   : 1
Total Blocks Influx           : 2
Message 531 not found;  product=RDBMS; facility=BBED

测试segment header坏块后select操作

SQL> select * from chf.t_xifenfei;
select * from chf.t_xifenfei
                         *
ERROR at line 1:
ORA-01578: ORACLE data block corrupted (file # 4, block # 170)
ORA-01110: data file 4: '/u01/oracle/oradata/ora11g/users01.dbf'

SQL> select /*+index(t PK_T_XIFENFEI)*/  count(rowid) from chf.t_xifenfei t;

COUNT(ROWID)
------------
       74762

基于rowid获取segment header 坏块对象数据

SQL> create table chf.bad_rows (table_name varchar2(60),
   2 row_id rowid, oracle_error_code number);

Table created.

SQL> DECLARE
  2   TYPE RowIDTab IS TABLE OF ROWID INDEX BY BINARY_INTEGER;
  3   CURSOR c1 IS  select /*+index(t PK_T_XIFENFEI)*/ rowid from chf.t_xifenfei t;
  4   r RowIDTab;
  5   rows  NATURAL := 20000;
  6   bad_rows number := 0 ;
  7   errors number;
  8   error_code number;
  9   myrowid rowid;
 10  BEGIN
 11   OPEN c1;
 12   LOOP
 13     FETCH  c1 BULK COLLECT INTO r LIMIT rows;
 14     EXIT WHEN r.count=0;
 15     BEGIN
 16      FORALL i IN r.FIRST..r.LAST SAVE EXCEPTIONS
 17       insert into chf.t_xifenfei_new
 18       select /*+ ROWID(A) */ *
 19       from chf.t_xifenfei A where rowid = r(i);
 20     EXCEPTION
 21     when OTHERS then
 22      BEGIN
 23       errors := SQL%BULK_EXCEPTIONS.COUNT;
 24       FOR err1 IN 1..errors LOOP
 25           error_code := SQL%BULK_EXCEPTIONS(err1).ERROR_CODE;
 26           myrowid := r(SQL%BULK_EXCEPTIONS(err1).ERROR_INDEX);
 27           bad_rows := bad_rows + 1;
 28           insert into chf.bad_rows values('chf.t_xifenfei',myrowid, error_code);
 29       END LOOP;
 30       END;
 31     END;
 32    commit;
 33   END LOOP;
 34   commit;
 35   CLOSE c1;
 36   dbms_output.put_line('Total Bad Rows: '||bad_rows);
 37  END;
 38  /
Total Bad Rows: 0

PL/SQL procedure successfully completed.

SQL> select count(*) from chf.t_xifenfei_new;

  COUNT(*)
----------
     74762

通过上面pl/sql，基于rowid成功获得segment header 异常对象中的所有数据记录.如果没有主键的表出现该问题,可以参考:使用plsql抢救数据