sys.fn_virtualfilestats (Transact-SQL)

THIS TOPIC APPLIES TO:yesSQL Server (starting with 2008)yesAzure SQL DatabasenoAzure SQL Data Warehouse noParallel Data Warehouse

Returns I/O statistics for database files, including log files. In SQL Server, this information is also available from the sys.dm_io_virtual_file_stats dynamic management view.

Topic link icon Transact-SQL Syntax Conventions

Syntax


fn_virtualfilestats ( { database_id | NULL } , { file_id | NULL } )  

Arguments

database_id | NULL
Is the ID of the database. database_id is int, with no default. Specify NULL to return information for all databases in the instance of SQL Server.

file_id | NULL
Is the ID of the file. file_id is int, with no default. Specify NULL to return information for all files in the database.

Table Returned

Column Name Data type Description
DbId smallint Database ID.
FileId smallint File ID.
TimeStamp bigint Database timestamp at which the data was taken. int in versions before SQL Server 2016.
NumberReads bigint Number of reads issued on the file.
BytesRead bigint Number of bytes read issued on the file.
IoStallReadMS bigint Total amount of time, in milliseconds, that users waited for the read I/Os to complete on the file.
NumberWrites bigint Number of writes made on the file.
BytesWritten bigint Number of bytes written made on the file.
IoStallWriteMS bigint Total amount of time, in milliseconds, that users waited for the write I/Os to complete on the file.
IoStallMS bigint Sum of IoStallReadMS and IoStallWriteMS.
FileHandle bigint Value of the file handle.
BytesOnDisk bigint Physical file size (count of bytes) on disk.

For database files, this is the same value as size in sys.database_files, but is expressed in bytes rather than pages.

For database snapshot sparse files, this is the space the operating system is using for the file.

Remarks

fn_virtualfilestats is a system table-valued function that gives statistical information, such as the total number of I/Os performed on a file. You can use this function to help keep track of the length of time users have to wait to read or write to a file. The function also helps identify the files that encounter large numbers of I/O activity.

Permissions

Requires VIEW SERVER STATE permission on the server.

Examples

A. Displaying statistical information for a database

The following example displays statistical information for file ID 1 in the database with an ID of 1.

SELECT *  
FROM fn_virtualfilestats(1, 1);  
GO  

B. Displaying statistical information for a named database and file

The following example displays statistical information for the log file in the AdventureWorks2012 sample database. The system function DB_ID is used to specify the database_id parameter.

SELECT *  
FROM fn_virtualfilestats(DB_ID(N'AdventureWorks2012'), 2);  
GO  

C. Displaying statistical information for all databases and files

The following example displays statistical information for all files in all databases in the instance of SQL Server.

SELECT *  
FROM fn_virtualfilestats(NULL,NULL);  
GO  

See Also

DB_ID (Transact-SQL)
FILE_IDEX (Transact-SQL)
sys.database_files (Transact-SQL)
sys.master_files (Transact-SQL)