SQL Server Troubleshooting: Error 9004 Occurred due to Damage in Transaction Log

Introduction

Transaction logs in SQL database are the vital component consisting of all the changes a user makes in database. Moreover, user can undo the changes that he made in a file of the database using the information contained in the transaction logs; this operation is also a transaction. It can be understood by the following:

You have made some changes in the data file of a database, say DB1, it means that a transaction is taking place. The log begins keeping record by the time you start making changes till you perform commit of that transaction. Note that a database consists of minimum one data file and physical transaction log.

Now imagine that there is damage to transaction log, it will directly impact the database. If an operation is performed in SQL that requires processing or reading the transaction log, an error may occur similar to the following:

Error: 9004
An error occurred while processing the log for database.  If possible, restore from backup. If a backup is not available, it might be necessary to rebuild the log.

Root Cause of the Error

The error occurs in case of damage to contents of transaction log. The severity of the error is same as that of a database corruption. Therefore, for in-depth analysis of cause, the similar techniques should be applied that are required for database corruption.

What to do

Try out the following to work around this problem:

Restore from Backup

It is recommended to bring the backup into use. It might be the case that the backup of transaction log or its portion has created corruption in the contents of transaction log. In this case, Error 9004 may occur while restoring. It indicates that there is damage to transaction log placed in the backup.

Rebuild the Transaction Log

If it is not possible to restore from the backup, you can rebuild the transaction log. However, you need to be aware of all positives and negatives of doing it so that you can avoid possible transactional consistency loss in the database. Furthermore, it includes DBCC CHECKDB command to execute.

However, you might not be able to carry out the task successfully or even if you do, it might not give the expected results. If so, you can use commercial SQL recovery application. Such applications are the programs built by software experts. More of it, such software will perform recovery, which has been failed by DBCC CHECKDB command, it will also recover the database from suspect mode. You can also recover the database in case of severe damages.