---
title: "SET STATISTICS IO (Transact-SQL)"
description: "Use SET STATISTICS IO to display information about the amount of physical and logical IO activity generated by T-SQL statements."
author: WilliamDAssafMSFT
ms.author: wiassaf
ms.date: 06/07/2024
ms.service: sql
ms.subservice: 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).
  
 :::image type="icon" source="../../includes/media/topic-link-icon.svg" border="false"::: [Transact-SQL syntax conventions](../../t-sql/language-elements/transact-sql-syntax-conventions-transact-sql.md)  
  
## Syntax
  
```syntaxsql
SET STATISTICS IO { ON | OFF }
```  
  

## Output

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 /> 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 /> Scan count is N when N is the number of different seeks or scans started toward 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.|  
| `page server reads` |Number of pages read from page servers. \*\* |
| `read-ahead reads` |Number of pages placed into the cache by the query, via the [read-ahead](../../relational-databases/reading-pages.md).|  
| `page server read-ahead reads` |Number of pages read from page servers and placed into the data cache by the query, via the [read-ahead](../../relational-databases/reading-pages.md). \*\* |
| `lob logical reads` |Number of LOB\* pages read from the data cache. |  
| `lob physical reads` |Number of LOB\* pages read from disk.|  
| `lob page server reads` |Number of LOB\* pages read from page servers. \*\* |
| `lob read-ahead reads` |Number of LOB\* pages placed into the data cache by the query, via the [read-ahead](../../relational-databases/reading-pages.md).|
| `lob page server read-ahead reads` |Number of LOB\* pages read from page servers and placed into the data cache by the query, via the [read-ahead](../../relational-databases/reading-pages.md). \*\* |

\* Large object binary (LOB) data types include **text**, **ntext**, **image**, **varchar(max)**, **nvarchar(max)**, **varbinary(max)**, or columnstore index pages.

\*\* Non-zero for [!INCLUDE [ssazure-sqldb](../../includes/ssazure-sqldb.md)] Hyperscale only.

## 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 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 can 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 AdventureWorks2022;  
GO         
SET STATISTICS IO ON;  
GO  
SELECT *   
FROM Production.ProductCostHistory  
WHERE StandardCost < 500.00;  
GO  
SET STATISTICS IO OFF;  
GO  
```  
  
 Here is the message output:
  
```output
Table 'ProductCostHistory'. Scan count 1, logical reads 76, physical reads 0,
page server reads 0, read-ahead reads 0, page server read-ahead reads 0, 
lob logical reads 0, lob physical reads 0, lob page server reads 0, 
lob read-ahead reads 0, lob page server read-ahead reads 0.
```  
  
## Related content

- [SET Statements (Transact-SQL)](../../t-sql/statements/set-statements-transact-sql.md)
- [SET SHOWPLAN_ALL (Transact-SQL)](../../t-sql/statements/set-showplan-all-transact-sql.md)
- [SET STATISTICS TIME (Transact-SQL)](../../t-sql/statements/set-statistics-time-transact-sql.md)