Oracle Using DUL to Recover From Database Corruption (with some examples)

Posted by PDSERVICE on Nov 19, 2015 In

Table Of Contents

~~~~~~~~~~~~~~~~~

1. Introduction

2. Using DUL

2.1 Create an appropriate init.dul file

2.2 Create the control.dul file

2.3 Unload the object information

2.4 Invoke DUL

2.5 Rebuild the database

3. How to rebuild object definitions that are stored in the data dictionary ?

4. How to unload data when the segment header block is corrupted ?

5. How to unload data when the file header block is corrupted ?

6. How to unload data without the system tablespace ?

7. Appendix A : Where to find the executables ?

8. References

1. Introduction

~~~~~~~~~~~~~~~

This document is to explain how to use DUL rather than to give a full

explanation of Bernard's Data UnLoader capabilities.

This document is for internal use only and should not be given to customers at

any time, Dul should always be used by or under the supervision of a support

analyst.

DUL (Data UnLoader) is intended to retrieve data from the Oracle Database that

cannot be retrieved otherwise. This is not an alternative for the export

utility or SQL*Loader. The database may be corrupted but an individual data

block used must be 100% correct. During all unloading checks are made to make

sure that blocks are not corrupted and belong to the correct segment. If a

corrupted block is detected by DUL, an error message is printed in the loader

file and to the standard output, but this will not terminate the unloading of

the next row or block.

2. Using DUL

~~~~~~~~~~~~

First you must retrieve the necessary information about the objects that exists

in the database, these statistics will be loaded into the DUL dictionary to

unload the database objects.

This information is retrieved from the USER$, OBJ$, TAB$ and COL$ tables that

were created at database creation time, they can be unloaded based on the fact

that object numbers are fixed for these tables due to the rigid nature of sql.

bsq. DUL can find the information in the system tablespace, therefor the system

tablespace datafile(s) must be included in the control file, if this datafile(s)

is not present see chapter 6.

2.1 Create an appropriate "init.dul" file

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

REM Platform specific parameters (NT)

REM A List of parameters for the most common platforms can be obtained from

osd_big_endian_flag=false

osd_dba_file_bits=10

osd_c_struct_alignment=32

osd_file_leader_size=1

osd_word_size = 32

REM Sizes of dul dictionary caches. If one of these is too low startup will

REM fail.

dc_columns=2000000

dc_tables=10000

dc_objects=1000000

dc_users=400

dc_segments=100000

REM Location and filename of the control file, default value is control.dul

REM in the current directory

control_file = D:\Dul\control_orcl.dul

REM Database blocksize, can be found in the init<SID>.ora file or can be

REM retrieved by doing "show parameter %db_block_size%" in server manager

REM (svrmgr23/30/l) changes this parameter to whatever the block size is of

REM the crashed database.

db_block_size=4096

REM Can/must be specified when data is needed into export/import format.

REM this will create a file suitable to use by the oracle import utility,

REM although the generated file is completely different from a table mode

REM export generated by the EXP utility. It is a single table dump file

REM with only a create table structure statement and the table data.

REM Grants, storage clauses, triggers are not included into this dump file !

export_mode=true

REM Compatible parameter must be specified an can be either 6, 7 or 8

compatible=8

REM This parameter is optional and can be specified on platforms that do

REM not support long file names (e.g. 8.3 DOS) or when the file format that

REM DUL uses "owner_name.table_name.ext" is not acceptable. The dump files

REM will be something like dump001.ext, dump002.ext, etc in this case.

file = dump

html section "DUL Parameters" although this init.dul file will work in most

cases and contains all accurate parameters to succesfully complete the

unloading.

2.2 Create the "control.dul" file

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A good knowledge about the logical tablespace and physical datafile

structure is needed or you can do the following queries when the database

is mounted :

Oracle 6, 7

-----------

> connect internal

> spool control.DUL

> select * from v$dbfile;

> spool off

Oracle 8

--------

> connect internal

> spool control.dul

> select ts#, rfile#, name from v$datafile;

> spool off

Edit the spool file and change, if needed, the datafile location and stripe

out unnecessary information like table headers, feedback line, etc...

A sample control file looks something like this :

REM Oracle7 control file

1 D:\DUL\DATAFILE\SYS1ORCL.DBF

3 D:\DUL\DATAFILE\DAT1ORCL.DBF

7 D:\DUL\DATAFILE\USR1ORCL.DBF

REM Oracle8 control file

0 1 D:\DUL\DATAFILE\SYS1ORCL.DBF

1 2 D:\DUL\DATAFILE\USR1ORCL.DBF

1 3 D:\DUL\DATAFILE\USR2ORCL.DBF

2 4 D:\DUL\DATAFILE\DAT1ORCL.DBF

Note : Each entry can contain a part of a datafile, this can be useful when

you need to split datafiles that are too big for DUL, so that each

part is smaller than for example 2GB. For example :

REM Oracle8 with a datafile split into multiple parts, each part is

REM smaller than 1GB !

0 1 D:\DUL\DATAFILE\SYS1ORCL.DBF

1 2 D:\DUL\DATAFILE\USR1ORCL.DBF startblock 1 endblock 1000000

1 2 D:\DUL\DATAFILE\USR1ORCL.DBF startblock 1000001 endblock 2000000

1 2 D:\DUL\DATAFILE\USR1ORCL.DBF startblock 2000001 endblock 2550000

2.3 Unload the object information

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Start the DUL utility with the appropriate ddl (Dul Description Language)

script. There are 3 scripts available to unload the USER$, OBJ$, TAB$ and

COL$ tables according to the database version.

Oracle6 :> dul8.exe dictv6.ddl

Oracle7 :> dul8.exe dictv7.ddl

Oracle8 :> dul8.exe dictv8.ddl

Data UnLoader: Release 8.0.5.3.0 - Internal Use Only - on Tue Jun 22 22:19:

Parameter altered

Session altered.

Parameter altered

Session altered.

Parameter altered

Session altered.

Parameter altered

Session altered.

. unloading table OBJ$ 2271 rows unloaded

. unloading table TAB$ 245 rows unloaded

. unloading table COL$ 10489 rows unloaded

. unloading table USER$ 22 rows unloaded

. unloading table TABPART$ 0 rows unloaded

. unloading table IND$ 274 rows unloaded

. unloading table ICOL$ 514 rows unloaded

. unloading table LOB$ 13 rows unloaded

Life is DUL without it

This will unload the data of the USER$, OBJ$, TAB$ and COl$ data dictionary

tables into SQL*Loader files , this can not be manipulated into dump files

of the import format. The parameter export_mode = false is hardcoded into

the ddl scripts and can not be changed to the value "true" since this will

cause DUL to fail with the error:

. unloading table OBJ$

DUL: Error: Column "DATAOBJ#" actual size(2) greater than length in column

definition(1)

.............etc...............

2.4 Invoke DUL

~~~~~~~~~~~~~~

Start DUL in interactive mode or you can prepare a scripts that contains all

the ddl commands to unload the necessary data from the database. I will

describe in this document the most used commands, this is not a complete list

of possible parameters that can be specified. A complete list can be found at

section "DDL Description".

DUL> unload database;

=> this will unload the entire database tables(includes sys'tables as well)

DUL> unload user <username>;

=> this will unload all the tables owned by that particullarly user.

DUL> unload table <username.table_name>;

=> this will unload the specified table owned by that username

DUL> describe <owner_name.table_name>;

=> will represent the table columns with there relative pointers to the

datafile(s) owned by the specified user.

DUL> scan database;

=> Scans all blocks of all data files.

Two files are generated:

1: seg.dat information of found segment headers (index/cluster/table)

(object id, file number, and block number).

2: ext.dat information of contiguous table/cluster data blocks.

(object id(V7), file and block number of segment header (V6),

file number and block number of first block,

number of blocks, number of tables)

DUL> scan tables;

=> Uses seg.dat and ext.dat as input.

Scans all tables in all data segments (a header block and at least one

matching extent with at least 1 table).

2.5 Rebuild the database

~~~~~~~~~~~~~~~~~~~~~~~~

Create the new database and use import or SQL*Loader to restore the data

retrieved by DUL. Note that when you only unloaded the data that table

structures, indexation, grants, PL/SQL and triggers will no longer exist in

the new database. To obtain an exactly same copy of the database as before

you will need to rerun your creation scripts for the tables, indexes, PL/SQL,

etc.

If you don't have these scripts then you will need to perform the steps

described in section 3 of this document.

3. How to rebuild object definitions that are stored in the data dictionary

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You want to rebuild PL/SQL(packages, procedures, functions or triggers), grants,

indexes, constraints or storage clauses(old table structure) with DUL. This can

be done but is a little bit tricky. You need to unload the relevant data

dictionary tables using DUL and then load these tables into a healthy database,

be sure to use a different user than sys or (system). Loading the data

dictionary tables of the crashed database into the healthy database dictionary

could corrupt the healthy database as well.

Detailed explanation to retrieve for example pl/sql packages / procedures /

functions from a corrupted database :

1) Follow the steps explained in the "Using DUL" section and unload the data

dictionary table "source$"

2) Create a new user into a healthy database and specify the desired default

and temporary tablespace.

3) Grant connect, resource, imp_full_database to the new user.

4) Import/load the table "source$" into the new created schema:

e.g.: imp80 userid=newuser/passw file=d:\dul\scott_emp.dmp

log=d:\dul\impemp.txt full=y

5) You can now query from the table <newuser.source$> to rebuild the pl/sql

procedures/functions from the corrupted database. Scripts can be found on

WebIv to generate such PL/SQL creation scripts.

The same steps can be followed to recreate indexes, constraints, and storage

parameters or to regrant privileges to the appropiate users. Please notice that

you always need to use a script of some kind that can recreate the objects and

include all the features of the crashed database version. For example : when

the crashed database is of version 7.3.4 and you have several bitmap indexes,

if you would use a script that supports version 7.3.2 or prior, then you won't

be able to recreate the bitmap indexes succesful !

4. How to unload data when the segment header block is corrupted

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When DUL can't retrieve data block information on the normal way, it can scan

the database to create its own segment/extent map. The procedure of scanning

the database is necessary to unload the data from the datafiles.

(to illustrate this example I copied an empty block ontop of the segment header

block)

1) Create an appropiate "init.dul" (see 2.1) and "control.dul" (see 2.2) file.

2) Unload the table. This will fail and indicate that there is a corruption in

the segment header block:

DUL> unload table scott.emp;

. unloading table EMP

DUL: Warning: Block is never used, block type is zero

DUL: Error: While checking tablespace 6 file 10 block 2

DUL: Error: While processing block ts#=6, file#=10, block#=2

DUL: Error: Could not read/parse segment header

0 rows unloaded

3) run the scan database command :

DUL> scan database;

tablespace 0, data file 1: 10239 blocks scanned

tablespace 6, data file 10: 2559 blocks scanned

4) Indicate to DUL that it should use its own generated extent map rather than

the segment header information.

DUL> alter session set use_scanned_extent_map = true;

Parameter altered

Session altered.

DUL> unload table scott.emp;

. unloading table EMP 14 rows unloaded

5. How to unload data when the datafile header block is corrupted

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A corruption in the datafile header block is always listed at the moment you

open the database this is not like a header segment block corruption (see point

4) where the database can be succesfully openend and the corruption is listed

at the moment you do a query of a table. Dul has no problems with recovering

from such situations although there are other alternatives of recovering from

this situation like patching the datafile header block.

The error you will receive looks something like :

ORACLE instance started.

Total System Global Area 11739136 bytes

Fixed Size 49152 bytes

Variable Size 7421952 bytes

Database Buffers 4194304 bytes

Redo Buffers 73728 bytes

Database mounted.

ORA-01122: database file 10 failed verification check

ORA-01110: data file 10: 'D:\DATA\TRGT\DATAFILES\JUR1TRGT.DBF'

ORA-01251: Unknown File Header Version read for file number 10

6. How to unload data without the system tablespace

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If datafiles are not available for the system tablespace the unload can still

continue but the object information can't be retrieved from the data dictionary

tables USER$, OBJ$, TAB$ and COL$. So ownername, tablename and columnnames will

not be loaded into the DUL dictionary. Identifying the tables can be an

overwhelming task and a good knowledge of the RDBMS internals are needed here.

First of all you need a good knowledge of your application and it's tables.

Column types can be guessed by DUL, but table and column names will be lost.

Any old system tablespace from the same database (may be weeks old) can be a

great help !

1) Create the "init.dul" file and the "control.dul" file as explained in above

steps 1 and 2. In this case the control file will contain all the datafiles

from which you want to restore but it doesn't require the system tablespace

information.

2) Then You invoke dul and type the following command :

DUL> scan database;

data file 6 1280 blocks scanned

This will build the extent and segment map. Probably the dul command

interpreter will be terminated as well.

3) reinvoke the dul command interpreter and do the following :

Data UnLoader: Release 8.0.5.3.0 - Internal Use Only - on Tue Aug 03 13:33:

Loaded 4 segments

Loaded 2 extents

Extent map sorted

DUL> alter session set use_scanned_extent_map = true;

DUL> scan tables; (or scan extents;)

Scanning tables with segment header

Oid 1078 fno 6 bno 2 table number 0

UNLOAD TABLE T_O1078 ( C1 NUMBER, C2 UNKNOWN, C3 UNKNOWN )

STORAGE ( TABNO 0 EXTENTS( FILE 6 BLOCK 2));

Colno Seen MaxIntSz Null% C75% C100 Num% NiNu% Dat% Rid%

1 4 2 0% 0% 0% 100% 100% 0% 0%

2 4 10 0% 100% 100% 100% 0% 0% 0%

3 4 8 0% 100% 100% 100% 0% 0% 50%

"10" "ACCOUNTING" "NEW YORK"

"20" "RESEARCH" "DALLAS"

"30" "SALES" "CHICAGO"

"40" "OPERATIONS" "BOSTON"

Oid 1080 fno 6 bno 12 table number 0

UNLOAD TABLE T_O1080 ( C1 NUMBER, C2 UNKNOWN, C3 UNKNOWN, C4 NUMBER,

C5 DATE, C6 NUMBER, C7 NUMBER, C8 NUMBER )

STORAGE ( TABNO 0 EXTENTS( FILE 6 BLOCK 12));

Colno Seen MaxIntSz Null% C75% C100 Num% NiNu% Dat% Rid%

1 14 3 0% 0% 0% 100% 100% 0% 0%

2 14 6 0% 100% 100% 100% 0% 0% 21%

3 14 9 0% 100% 100% 100% 0% 0% 0%

4 14 3 7% 0% 0% 100% 100% 0% 0%

5 14 7 0% 0% 0% 0% 0% 100% 0%

6 14 3 0% 0% 0% 100% 100% 0% 0%

7 14 2 71% 0% 0% 100% 100% 0% 0%

8 14 2 0% 0% 0% 100% 100% 0% 0%

"7369" "SMITH" "CLERK" "7902" "17-DEC-1980 AD 00:00:00" "800" "" "20"

"7499" "ALLEN" "SALESMAN" "7698" "20-FEB-1981 AD 00:00:00" "1600" "300" "30"

"7521" "WARD" "SALESMAN" "7698" "22-FEB-1981 AD 00:00:00" "1250" "500" "30"

"7566" "JONES" "MANAGER" "7839" "02-APR-1981 AD 00:00:00" "2975" "" "20"

"7654" "MARTIN" "SALESMAN" "7698" "28-SEP-1981 AD 00:00:00" "1250" "1400" "30"

Note : it might be best that you redirect the output to a logfile since

commands like the "scan tables" can produce a lot of output.

On Windows NT you can do the following command :

C:\> dul8 > c:\temp\scan_tables.txt

scan tables;

exit;

4) Identify the lost tables from the output of step 3; if you look carefully to

the output above then you will notice that the unload syntax is already given

but that the table name will be of the format t_0<objectno> and the column

names will be of the format C<no>; datatypes will not be an exact match of

the datatype as it was before.

Look especially for strings like "Oid 1078 fno 6 bno 2 table number 0" where:

oid = object id, will be used to unload the object

fno = (data)file number

bno = block number

5) Unload the identified tables with the "unload table" command :

DUL> unload table dept (deptno number(2), dname varchar2(14),

loc varchar2(13)) storage (OBJNO 1078)

Unloading extent(s) of table DEPT 4 rows.

7. Appendix A : Where to find the executables

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The executables can be found at the dutch intranet site

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Oracle Using DUL to Recover From Database Corruption (with some examples)

Oracle Using DUL to Recover From Database Corruption (with some examples)