SET STATISTICS IO (Transact-SQL)
Applies To: SQL Server 2014, SQL Server 2016 Preview
Causes SQL Server to display information regarding the amount of disk activity generated by Transact-SQL statements.
Applies to: SQL Server (SQL Server 2008 through current version), Azure SQL Database.
When STATISTICS IO is ON, statistical information is displayed. When OFF, the information is not displayed.
After this option is set ON, all subsequent Transact-SQL statements return the statistical information until the option is set to OFF.
The following table lists and describes the output items.
Name of the table.
Number of seeks/scans started after reaching the leaf level in any direction to retrieve all the values to construct the final dataset for the output.
Number of pages read from the data cache.
Number of pages read from disk.
Number of pages placed into the cache for the query.
lob logical reads
Number of text, ntext, image, or large value type (varchar(max), nvarchar(max), varbinary(max)) pages read from the data cache.
lob physical reads
Number of text, ntext, image or large value type pages read from disk.
lob read-ahead reads
Number of text, ntext, image or large value type pages placed into the cache for the query.
The setting of SET STATISTICS IO is set at execute or run time and not at parse time.
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.
To use SET STATISTICS IO, users must have the appropriate permissions to execute the Transact-SQL statement. The SHOWPLAN permission is not required.
This example shows how many logical and physical reads are used by SQL Server as it processes the statements.
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.