Monday, November 7, 2011

General scenarios leading to Oracle database corruption and a few recovery measures

Oracle, when compared to other database systems, has the capability of running and handling more transactions. Besides acquiring less resources, it can effectively handle memory leaks and multiple threads. Oracle provides powerful tools to easily and quickly backup your entire database, which could take sufficient amount of time if you use MySQL or any other database system. Despite incorporating several user-specific benefits, Oracle databases might get corrupt in the event of a virus infection, hardware malfunction, or abnormal system shutdown. In such circumstances, all vital objects in the database become inaccessible. To overcome this problem, you need to go for Oracle recovery through a reliable third-party utility.

Corruption usually occurs in the Oracle data block that has to pass through a number of communication points. These blocks comprise the most fundamental components of an Oracle database. Each block contains one block directory, block header, some free space, and a transaction list (or ITL).

Oracle data block may get damaged or corrupt due to any of the following reasons:
  • A hardware component has malfunctioned.
  • The system has some incompatible device drivers.
  • You are facing several paging and memory issues.

This would certainly render your Oracle database inaccessible and as a result, you won't be able to access the valuable objects and other information stored therein. At this stage, you may use a backup to restore the database. However, if the backup is missing, you should follow the below mentioned resolution steps.

Resolution: Try the following steps to resolve this problem-

DBVerify: The utility helps to verify the integrity of offline data files and backup data files of the Oracle database.
ANALYZE...VALIDATE structure: You can use this tool to verify each data block in the analyzed object.
DB_BLOCK_CHECKING: You can set this argument to 'TRUE' for verifying the consistency of data in the Oracle data block. This might add to the server overhead.
DBMS_REPAIR: This is a very helpful tool to fix Oracle database corruption. The process would make a list of damaged blocks and their corresponding index keys.

If the problem still persists, you should take help of competent Oracle database recovery software. These third-party tools use highly safe mechanisms to perform a complete repair of corrupt Oracle database.

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