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description sys.dm_io_virtual_file_stats (Transact-SQL)
title sys.dm_io_virtual_file_stats (Transact-SQL) | Microsoft Docs
ms.custom
ms.date 04/21/2021
ms.prod sql
ms.prod_service database-engine, sql-database, synapse-analytics
ms.reviewer
ms.technology system-objects
ms.topic reference
f1_keywords
dm_io_virtual_file_stats
sys.dm_io_virtual_file_stats_TSQL
sys.dm_io_virtual_file_stats
dm_io_virtual_file_stats_TSQL
dev_langs
TSQL
helpviewer_keywords
sys.dm_io_virtual_file_stats dynamic management function
ms.assetid fa3e321f-6fe5-45ff-b397-02a0dd3d6b7d
author WilliamDAssafMSFT
ms.author wiassaf
monikerRange =azuresqldb-current||=azure-sqldw-latest||>= aps-pdw-2016||>=sql-server-2016||>=sql-server-linux-2017||=azuresqldb-mi-current

sys.dm_io_virtual_file_stats (Transact-SQL)

[!INCLUDE sql-asdb-asdbmi-asa-pdw]

Returns I/O statistics for data and log files. This dynamic management function replaces the fn_virtualfilestats function.

Note

To call this from [!INCLUDEssSDWfull], use the name sys.dm_pdw_nodes_io_virtual_file_stats. [!INCLUDEsynapse-analytics-od-unsupported-syntax]

Syntax

-- Syntax for SQL Server and Azure SQL Database

sys.dm_io_virtual_file_stats (   
    { database_id | NULL },  
    { file_id | NULL }  
)  

-- Syntax for Azure Synapse Analytics

sys.dm_pdw_nodes_io_virtual_file_stats

Arguments

database_id | NULL

APPLIES TO: SQL Server (starting with 2008), Azure SQL Database

ID of the database. database_id is int, with no default. Valid inputs are the ID number of a database or NULL. When NULL is specified, all databases in the instance of [!INCLUDEssNoVersion] are returned.

The built-in function DB_ID can be specified.

file_id | NULL

APPLIES TO: SQL Server (starting with 2008), Azure SQL Database

ID of the file. file_id is int, with no default. Valid inputs are the ID number of a file or NULL. When NULL is specified, all files on the database are returned.

The built-in function FILE_IDEX can be specified, and refers to a file in the current database.

Table Returned

Column name Data type Description
database_name sysname Does not apply to:: [!INCLUDEssNoVersion].

Database name.

For Azure Synapse Analytics, this is the name of the database stored on the node which is identified by pdw_node_id. Each node has one tempdb database that has 13 files. Each node also has one database per distribution, and each distribution database has 5 files. For example, if each node contains 4 distributions, the results show 20 distribution database files per pdw_node_id.
database_id smallint ID of database.
file_id smallint ID of file.
sample_ms bigint Number of milliseconds since the computer was started. This column can be used to compare different outputs from this function.

The data type is int for [!INCLUDEssKatmai] through [!INCLUDEssSQL14]. In these versions, the value will reset to 0 after approximately 25 days of continuous database engine uptime.
num_of_reads bigint Number of reads issued on the file.
num_of_bytes_read bigint Total number of bytes read on this file.
io_stall_read_ms bigint Total time, in milliseconds, that the users waited for reads issued on the file.
num_of_writes bigint Number of writes made on this file.
num_of_bytes_written bigint Total number of bytes written to the file.
io_stall_write_ms bigint Total time, in milliseconds, that users waited for writes to be completed on the file.
io_stall bigint Total time, in milliseconds, that users waited for I/O to be completed on the file.
size_on_disk_bytes bigint Number of bytes used on the disk for this file. For sparse files, this number is the actual number of bytes on the disk that are used for database snapshots.
file_handle varbinary Windows file handle for this file.
io_stall_queued_read_ms bigint Does not apply to:: [!INCLUDEssKatmai] through [!INCLUDEssSQL12].

Total IO latency introduced by IO resource governance for reads. Is not nullable. For more information, see sys.dm_resource_governor_resource_pools (Transact-SQL).
io_stall_queued_write_ms bigint Does not apply to:: [!INCLUDEssKatmai] through [!INCLUDEssSQL12].

Total IO latency introduced by IO resource governance for writes. Is not nullable.
pdw_node_id int Applies to: [!INCLUDEssSDW]

Identifier of the node for the distribution.

Remarks

The counters are initialized to empty whenever the SQL Server (MSSQLSERVER) service is started.

Permissions

Requires VIEW SERVER STATE permission. For more information, see Dynamic Management Views and Functions (Transact-SQL).

Examples

A. Return statistics for a log file

Applies to: SQL Server (starting with 2008), Azure SQL Database

The following example returns statistics for the log file in the [!INCLUDEssSampleDBnormal] database.

SELECT * FROM sys.dm_io_virtual_file_stats(DB_ID(N'AdventureWorks2012'), 2);  
GO

B. Return statistics for file in tempdb

Applies to: Azure Synapse Analytics

SELECT * FROM sys.dm_pdw_nodes_io_virtual_file_stats 
WHERE database_name = 'tempdb' AND file_id = 2;

See Also

Dynamic Management Views and Functions (Transact-SQL)
I O Related Dynamic Management Views and Functions (Transact-SQL)
sys.database_files (Transact-SQL)
sys.master_files (Transact-SQL)