How to Detect Virtual Log Files in SQL Server Transaction Log File


Aug 17, 2012

Introduction

This article demonstrates how to Detect Virtual Log Files in SQL Server Transaction Log File. The steps mentioned in this article are applicable on SQL Server 2005 and higher versions. To know more about how to fix Virtual Log File in SQL Server Transaction Log File refer the following article “How to Fix Virtual Log Files in SQL Server Transactional Log file”.

How to Identify Virtual Log Files in SQL Server Transaction Log File

Using DBCC LOGINFO command a DBA can easily identify the number of Virtual Log Files (VLF) which are presently available within a Transaction Log file of SQL Server database.

For this demo, the size of the sample database is 2 GB and the size of the Transactional Log file was 700 MB.

Query to Identify Virtual Log Files in Transaction Log File

Use BPO
GO

DBCC LOGINFO
GO

In the below snippet you could see that BPO database had 196 Virtual Log Files. The reason why this database had so many Virtual Log Files was that initial the log file growth was kept very small i.e. 1MB initial size and allow it to grow 10% every time whenever there is a need. This wrong Autogrowth setting had resulted in frequent log file growth and this ended up creating too many small Virtual Log Files of small size. However, this wrong Auto Growth setting for Transactional Log file has resulted in Transactional Log Files getting fragmented. To change Auto Growth settings for Data and Transactional log file refer the following article "How to Change SQL Server Database Auto Growth Settings".

How to Identify Virtual Log Files in SQL Server Transactional Log File

This scenario can result in slow recovery of the database when the database is started as it will have to recover a very large volume of work. Moreover, the performance of the database will be affected when the query runs which results in Transaction log file growth. For more information on this refer the following Microsoft KB.

Performance Improvement Tips: - Configuring Database Instant File Initialization Feature of SQL Server to improve the time taken to grow data and log files.

It is not a good practice to have such a large number of Virtual Log Files in a database. Ideally a database should have Virtual Log File in a range of 25 – 50. Smaller Autogrowth settings will impact Performance of the database during recovery and well as bring in timeout issues when the log file growth takes longer time.

Read the following article which explains "How to Fix Virtual Log Files in SQL Server Transactional Log file"

Conclusion

In this article you have seen how you can identify the number of virtual log files in SQL Server Transaction Log file. To fix this issue refer the following "How to Fix Virtual Log Files in SQL Server Transactional Log file" article.

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