DUL Introduction

Posted on June 14, 2008

• Developed by Bernard Van Duijnen
• Is a stand-alone disaster recovery utility, and
• requires no other Oracle software to run
• Unloads data from data files of a crashed database
• Creates SQL*Loader control files and data files

A useful utility has been developed in the Netherlands, called the Data Recovery
Unloader (DUL). DUL is a stand-alone C program that directly retrieves rows from
tables in data files. The RDBMS is not necessary.
DUL is intended to retrieve data from the database that cannot otherwise be retrieved.
The database may be corrupted, but an individual data block to be used by DUL must
be 100% correct.
DUL unloads data from files containing table and cluster data. It creates no scripts for
triggers, procedures, tables, and views; it can only read the definitions from the data
dictionary tables.
DUL can create SQL*Loader files or export files.
When to Use DUL
You can use DUL in disaster scenarios to provide your customer more current data
than the last backup or export.
Before using DUL, you will need to learn more about the ACID principle (Atomicity,
Consistency, Isolation, and Durability), Oracle’s transaction internals, block structures
(headers and footers), file structures, and OS file systems. These topics are discussed
in more detail in the DSI402 and DSI402e courses.

Also, make sure that your database is really unrecoverable. Recovery is discussed in
the DSI403 and DSI403e courses. Maybe your database can also be rescued by using
utilities like BBED and ORAPATCH, as discussed in DSI401.
DUL Requirements
You need the most current data files, preferably all of them from the same time frame.
You need a knowledgeable resource to discuss OS, database, and schema details. You
also need a new instance or location to put everything back together, with a lot of free
disk space (up to three times the size of your database.)
Good Things to Have
• Data file listing
• DDL scripts to re-create objects
• Any export of the instance; ancient is acceptable
• Idea of how much data is to be retrieved
• Patience and luck

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