What is the use of VLF in SQL Server?

What are VLF in SQL Server?

Virtual Log File Overview In SQL Server, each transaction log is logically divided into smaller segments, in which the log records are written. These small segments are called SQL Virtual Log Files, also known as VLFs.

How many VLFs are too many?

The threshold for significantly impacting the recovery performance appears to be somewhere around ten thousand VLFs. No symptoms are felt when there are a few thousand VLFs or less. When there are around a hundred thousand VLFs, the symptoms become substantially noticed.

How do you calculate VLF count?

How to identify the issue?1SELECT [name] AS 'Database Name',2COUNT(l. ... 3SUM(CAST(vlf_active AS INT)) AS 'Active VLF',4COUNT(l. ... 5SUM(vlf_size_mb) AS 'VLF Size (MB)',6SUM(vlf_active*vlf_size_mb) AS 'Active VLF Size (MB)',7SUM(vlf_size_mb)-SUM(vlf_active*vlf_size_mb) AS 'Inactive VLF Size (MB)'8FROM sys.How high VLF counts kill your SQL Performance | Red9

How do I find the VLF file in SQL Server?

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.