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CLR function to delete older backup and log files in SQL Server

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In a previous tip we looked at how to put together a CLR function for sorting text data.  In addition, we have also written tips about how to mimic the functionality of maintenance plans without having to use a maintenance plan.  In one of these previous tips, "Maintenance task to delete old backup files" we outlined how to delete older backup files by using a VB Script.  To take this deleting of older files a step further, this tip will look at this same task to remove older backup and log files, but this time using a CLR function.

If you have not yet built a CLR function, please refer to this tip for what needs to be done for the initial setup.

CLR Functions - Getting started with a string sort function

In this CLR function we are going to pass in a few parameters such as:

  • File path
  • Days to keep files
  • File Extension

and return a count of the number of files that were deleted.

Step 1 - CLR code

The first thing we need to do is to write the CLR code for this.  This could be written in either C#.NET or VB.NET.  In this example we are using VB.NET.

The following code has a Class (CLRFunctions) and a Function (DeleteFiles).  The function takes three parameters and returns an integer value.

Copy and save the code below in a file called:  C:\CLRFunctions.vb

Imports System.IO 

Public Class CLRFunctions    

Public Shared Function DeleteFiles(sPath As StringiDaysToKeep As IntegersFileExtension As StringAs Integer   

arrFiles As Array 
Dim dateToday As Date 
myFileInfo As FileInfo 
Dim myDirectoryInfo As DirectoryInfo 
Dim iFileCount As Integer 


= New DirectoryInfo(sPath

arrFiles myDirectoryInfo.GetFiles() 

dateToday DateAdd("d", -iDaysToKeepToday

For Each myFileInfo In arrFiles 
If myFileInfo.Extension sFileExtension And myFileInfo.LastWriteTime dateToday Then 
iFileCount iFileCount 1                 
End If 

Return 0         
End Try

End Function   



Step 2 - Compile CLR Code

In order to use this code, the code has to be compiled first. 

The following command is run from a command line to compile the CLR code using the vbc.exe application.  This is found in the .NET 2.0 framework directory.  This may be different on your server or desktop.  Also, this code should be compiled on the machine where the code will run.

So from a command line run a command such as the following:

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\vbc /target:library C:\CLRFunctions.vb

The code should now be compiled in a file called: C:\CLRFunctions.dll


Step 3 - Create Assembly and Function

After the code has been compiled you need to create the assembly and the function with SQL Server.  To do this, run these commands in the database where you want to use the function. 

The assembly ties an internal object to the external DLL that was created and the function is similar to a normal SQL Server function.

For the function you will see three components that are referenced CLRFunctions.CLRFunctions.DeleteFiles.

  • CLRFunctions - the assembly reference
  • CLRFunctions - the class reference in the VB code
  • DeleteFiles - the function reference in the VB code
CREATE ASSEMBLY CLRFunctions FROM 'C:\CLRFunctions.dll' 

CREATE FUNCTION dbo.DeleteFiles   
@FolderPath AS NVARCHAR(100),
@DaysToKeep AS integer,
@FileExtension AS NVARCHAR(50)   
RETURNS integer  
AS EXTERNAL NAME CLRFunctions.CLRFunctions.DeleteFiles

If you get error messages when trying to compile the code you may need to alter the database using the following command and then try again to create the assembly and the function.

ALTER DATABASE test1 SET trustworthy ON


Step 4 - Test It

To test the function, run the following SELECT statement based on the values you want to pass into the function.

In this example we are deleting files in the "C:\Backups" folder that are 14 days or older and have an extension of ".BAK"

SELECT dbo.DeleteFiles('C:\Backups'14'.BAK'AS FilesDeleted

In this example we are deleting files in the "C:\Backups" folder that are 7 days or older and have an extension of ".trn"

SELECT dbo.DeleteFiles('C:\Backups'7'.trn'AS FilesDeleted

In this example we are deleting files in the "C:\Backups" folder that are 14 days or older and have an extension of ".LOG"

SELECT dbo.DeleteFiles('C:\Backups', 14, '.LOG'AS FilesDeleted


Step 5 - Cleanup

To get rid of the code you will need to delete the DLL that is created from the compile step as well as the VB file that was created. 

In addition, run this T-SQL code to drop the objects that were created.

DROP FUNCTION dbo.DeleteFiles 



That's all there is to creating a CLR function to delete older backup files. This function as built only looks in one directory as well as only deals with one type of file extension at a time, so these are some things that could be done to improve this code.

One thing to note is that when the files are deleted they are not put into the recycle bin, so make sure you test this in a test environment to make sure you understand what is occurring before you implement this on your production servers.

Next Steps

  • Give this example a try and see what other functions you could write that could take advantage of the CLR
  • IF you have some enhancements to this function that you would like to share, please post them in this forum http://blogs.mssqltips.com/forums/t/65.aspx
  • If you have CLR functions that you want to share with the rest of the MSSQLTips.com community, please send them to [email protected] so we can post them for others to use or post them in the forums. 
  • If you don't know how to write either VB or C# now is the time to begin learning.


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About the author
MSSQLTips author Greg Robidoux Greg Robidoux is the President of Edgewood Solutions and a co-founder of MSSQLTips.com.

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