某系统由于存储损坏导致一个大对象LOB的LOB INDEX存在坏块corruption，且该系统无任何有效之备份。此时若要恢复对BLOB/CLOB中的数据则无法使用常规的方法，这里可以使用PRM-DUL 工具(http://www.parnassusdata.com/)来恢复其中数据。
场景重现为如下：
select * from BASE_CUSTOMERS_PHOTO where outid='XXXXXX'
select count(*) from BASE_CUSTOMERS_PHOTO
28050
此时对LOB INDEX 做彻底破坏
SQL> select INDEX_NAME from dba_lobs where table_name='BASE_CUSTOMERS_PHOTO';
INDEX_NAME
------------------------------
SYS_IL0000094755C00003$$
SQL> select header_file,header_block from dba_segments where segment_name='SYS_IL0000094755C00003$$';
HEADER_FILE HEADER_BLOCK
----------- ------------
6 879546
[oracle@ocp ~]$ rman target /
Recovery Manager: Release 11.2.0.4.0 - Production on Wed Jul 13 15:14:13 2016
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
connected to target database: GBK2 (DBID=717109662)
RMAN> recover datafile 6 block 879546 clear;
Starting recover at 13-JUL-16
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=150 device type=DISK
Finished recover at 13-JUL-16
[oracle@ocp ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Wed Jul 13 15:14:40 2016
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> alter system flush buffer_cache;
System altered.
SQL> select data_object_id from dba_objects where object_name='SYS_IL0000094755C00003$$';
DATA_OBJECT_ID
--------------
94757
SQL> desc ind$
Name Null? Type
----------------------------------------- -------- ----------------------------
OBJ# NOT NULL NUMBER
DATAOBJ# NUMBER
TS# NOT NULL NUMBER
FILE# NOT NULL NUMBER
BLOCK# NOT NULL NUMBER
BO# NOT NULL NUMBER
INDMETHOD# NOT NULL NUMBER
COLS NOT NULL NUMBER
PCTFREE$ NOT NULL NUMBER
INITRANS NOT NULL NUMBER
MAXTRANS NOT NULL NUMBER
PCTTHRES$ NUMBER
TYPE# NOT NULL NUMBER
FLAGS NOT NULL NUMBER
PROPERTY NOT NULL NUMBER
BLEVEL NUMBER
LEAFCNT NUMBER
DISTKEY NUMBER
LBLKKEY NUMBER
DBLKKEY NUMBER
CLUFAC NUMBER
ANALYZETIME DATE
SAMPLESIZE NUMBER
ROWCNT NUMBER
INTCOLS NOT NULL NUMBER
DEGREE NUMBER
INSTANCES NUMBER
TRUNCCNT NUMBER
SPARE1 NUMBER
SPARE2 NUMBER
SPARE3 NUMBER
SPARE4 VARCHAR2(1000)
SPARE5 VARCHAR2(1000)
SPARE6 DATE
SQL> select flags from ind$ where dataobj#=94757;
FLAGS
----------
0
SQL> update ind$ set flags=1 where dataobj#=94757;
1 row updated.
SQL> commit;
Commit complete.
SQL> select status from dba_indexes where index_name='SYS_IL0000094755C00003$$';
STATUS
--------
UNUSABLE
SQL> alter system flush shared_pool;
System altered.
SQL> alter system flush buffer_cache;
System altered.
此时启动PRM-DUL ，字典模式=》选择LOB所在表，选择Data Bridge，选择Base on LOB SCAN
这里使用based on lob scan的含义是基于PRM扫描LOb数据的信息去恢复数据，而不依赖于LOB INDEX的索引结构信息。