---
title: "SET STATISTICS IO (Transact-SQL)"
description: SET STATISTICS IO (Transact-SQL)
author: WilliamDAssafMSFT
ms.author: wiassaf
ms.date: "11/10/2016"
ms.prod: sql
ms.prod_service: "database-engine, sql-database"
ms.technology: t-sql
ms.topic: reference
f1_keywords:
  - "SET_STATISTICS_IO_TSQL"
  - "IO"
  - "IO_TSQL"
  - "SET STATISTICS IO"
helpviewer_keywords:
  - "disk I/O statistics [SQL Server]"
  - "I/O [SQL Server], disk activity information"
  - "disks [SQL Server], statement statistics"
  - "STATISTICS IO option"
  - "statements [SQL Server], statistical information"
  - "SET STATISTICS IO statement"
  - "statistical information [SQL Server], disk activity"
dev_langs:
  - "TSQL"
---
# SET STATISTICS IO (Transact-SQL)
[!INCLUDE [SQL Server Azure SQL Database Azure SQL Managed Instance](../../includes/applies-to-version/sql-asdb-asdbmi.md)]	

  Causes [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] to display information about the amount of physical and logical IO activity generated by [!INCLUDE[tsql](../../includes/tsql-md.md)] statements.  Physical IO is related to accessing data pages on disk and logical IO is related to accessing data pages in memory (data cache).
  
 ![Topic link icon](../../database-engine/configure-windows/media/topic-link.gif "Topic link icon") [Transact-SQL Syntax Conventions](../../t-sql/language-elements/transact-sql-syntax-conventions-transact-sql.md)  
  
## Syntax  
  
```syntaxsql
  
SET STATISTICS IO { ON | OFF }  
```  
  
[!INCLUDE[sql-server-tsql-previous-offline-documentation](../../includes/sql-server-tsql-previous-offline-documentation.md)]

## Remarks
 When STATISTICS IO is ON, statistical information is displayed, and when OFF, the information isn't displayed.   
  
 After this option is set ON, all [!INCLUDE[tsql](../../includes/tsql-md.md)] statements return the statistical information until the option is set to OFF.  
  
 The following table lists and describes the output items.  
  
|Output item|Meaning|  
|-----------------|-------------|  
|**Table**|Name of the table.|  
|**Scan count**|Number of seeks or scans started after reaching the leaf level in any direction to retrieve all the values to construct the final dataset for the output.<br /><br /> Scan count is 0 if the index used is a unique index or clustered index on a primary key and you're seeking for only one value. For example, `WHERE Primary_Key_Column = <value>`.<br /><br /> Scan count is 1 when you're searching for one value using a non-unique clustered index defined on a non-primary key column. This process is done to check for duplicate values for the key value that you're searching for. For example, `WHERE Clustered_Index_Key_Column = <value>`.<br /><br /> Scan count is N when N is the number of different seeks or scans started towards the left or right side at the leaf level after locating a key value using the index key.|  
|**logical reads**|Number of pages read from the data cache.|  
|**physical reads**|Number of pages read from disk.|  
|**read-ahead reads**|Number of pages placed into the cache for the query.|  
|**lob logical reads**|Number of pages read from the data cache. Includes **text**, **ntext**, **image**, **varchar(max)**, **nvarchar(max)**, **varbinary(max)**, or columnstore index pages.|  
|**lob physical reads**|Number of pages read from disk. Includes **text**, **ntext**, **image**, **varchar(max)**, **nvarchar(max)**, **varbinary(max)**, or columnstore index pages.|  
|**lob read-ahead reads**|Number of pages placed into the cache for the query. Includes **text**, **ntext**, **image**, **varchar(max)**, **nvarchar(max)**, **varbinary(max)**, or columnstore index pages.|

 The setting of SET STATISTICS IO is set at execute or run time and not at parse time.

> [!NOTE]  
> When Transact-SQL statements retrieve LOB columns, some LOB retrieval operations might require traversing the LOB tree multiple times. This may cause SET STATISTICS IO to report higher than expected logical reads.

## Permissions  
 To use SET STATISTICS IO, users must have the appropriate permissions to execute the [!INCLUDE[tsql](../../includes/tsql-md.md)] statement. The SHOWPLAN permission isn't required.  
  
## Examples  
 This example shows how many logical and physical reads are used by [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] as it processes the statements.  
  
```sql
USE AdventureWorks2012;  
GO         
SET STATISTICS IO ON;  
GO  
SELECT *   
FROM Production.ProductCostHistory  
WHERE StandardCost < 500.00;  
GO  
SET STATISTICS IO OFF;  
GO  
```  
  
 Here is the result set:  
  
```  
Table 'ProductCostHistory'. Scan count 1, logical reads 5, physical   
reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0,   
lob read-ahead reads 0.  
```  
  
## See Also  
 [SET Statements &#40;Transact-SQL&#41;](../../t-sql/statements/set-statements-transact-sql.md)   
 [SET SHOWPLAN_ALL &#40;Transact-SQL&#41;](../../t-sql/statements/set-showplan-all-transact-sql.md)   
 [SET STATISTICS TIME &#40;Transact-SQL&#41;](../../t-sql/statements/set-statistics-time-transact-sql.md)