Deep in the Code

As we are preparing to migrate some of our older SQL Server databases that are nearing their end of support to SQL Server 2019, one of the necessary tasks is determining what Linked Servers need to be established on the new servers to maintain the existing functionality for all of our users’ applications.

Testing the functionality of an individual Linked Server is simple enough – the built-in stored procedure sp_testlinkedserver will return a zero (0) if the link is good, and returns an exception if the link is not.

There is a stored procedure for listing all Linked Servers, but it doesn’t return the health of the link: sp_linkedservers.

How can these be combined to return only the Linked Servers that are currently up?

The solution I developed uses sp_linkedservers to populate a table variable, which is then used in a cursor. For each row in the table, using the sp_testlinkedserver stored proc, an active column is set to 1 if the server is up, and 0 if it is not.

DECLARE @LinkedServerName NVARCHAR(128), @Active BIT, @Message NVARCHAR(MAX)=''

DECLARE @Servers TABLE
(SRV_NAME NVARCHAR(128)
,SRV_PROVIDERNAME	NVARCHAR(128)
,SRV_PRODUCT	NVARCHAR(128)
,SRV_DATASOURCE	NVARCHAR(4000)
,SRV_PROVIDERSTRING	NVARCHAR(4000)
,SRV_LOCATION	NVARCHAR(4000)
,SRV_CAT	NVARCHAR(128)
,Active BIT DEFAULT 1)

INSERT INTO @Servers (SRV_NAME,SRV_PROVIDERNAME,SRV_PRODUCT,SRV_DATASOURCE,SRV_PROVIDERSTRING,SRV_LOCATION,SRV_CAT)
EXEC sp_linkedservers 

DECLARE servercursor CURSOR FOR 
	SELECT SRV_NAME, Active 
	FROM @Servers
	ORDER BY SRV_NAME

OPEN servercursor

FETCH NEXT FROM servercursor INTO @LinkedServerName, @Active
WHILE @@FETCH_STATUS=0
BEGIN
	DECLARE @isUp BIT = 0
		
	BEGIN TRY
		DECLARE @test INT
		EXEC @test = sp_testlinkedserver @LinkedServerName;
		IF @test = 0
			BEGIN
				SET @isUp = 1
			END
		ELSE
			BEGIN
				SET @isUp = 0
			END
	END TRY
	BEGIN CATCH			
		SET @isUp = 0;
	END CATCH
		
	IF @Active<>@isUp
	BEGIN
		UPDATE @Servers 
		SET Active=@isUp
		WHERE SRV_NAME=@LinkedServerName

		SET @Message = @Message + 'Active bit on server ' + @LinkedServerName + ' was set to ' + CONVERT(VARCHAR,@isUp) + '.' + CHAR(10) + CHAR(13)
	END		
	FETCH NEXT FROM servercursor INTO @LinkedServerName, @Active
END

CLOSE servercursor
DEALLOCATE servercursor

SELECT SRV_NAME
FROM @Servers
WHERE Active=1
ORDER BY SRV_NAME

PRINT @Message

Running this code will return an alphabetically ordered list of active linked servers.

What a long strange trip it’s been! Ten years ago today I made my first blog post here, and since then, I’ve learned quite a bit, and I hope that I’ve helped more than a few people with all the various and sundry issues that I’ve had during my adventures in software development.

In 2012, I was focused more on ASP.NET development, and my hope was that I’d get more involved with Objective-C and other Mac-related projects. While I did dabble there for a bit, it seems that the majority of my work has been with relational databases, some Oracle Database and the occasional MySQL issue, but mostly SQL Server.

It will be interesting to see where the next ten years takes me. Now I am learning more about Azure and Power BI, so I’m still heavily in the Microsoft world of technologies – and the road ahead looks bright.

Thanks for traveling with me on this journey!