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Using Dynamic T-SQL In A WHILE Loop
In my last post, I covered using xp_cmdshell to check the status of the SQL Server Agent service. I also mentioned my environment consists of more than 200 instances of SQL Server. The challenge I faced when developing this process was finding a way to check the Agent service on all instances from a central location. Fortunately, we have a central repository using linked servers to collect performance metrics. I will show how to use these linked servers to check Agent status. You can find the complete stored procedure code at the show source link at the bottom of the post. I will step through this code line by line.
The repository database has a table that contains all of the instances in the environment. The naming standard for linked servers in the environment is DUL + instance name. The following block of code selects all of the active instances names and prefixes them with DUL, inserting them into a temp table:
set @currentrow = 1 INSERT #serverlist SELECT 'DUL' + dpc_sql_cluster_nm FROM duddba_master.dbo.DUT_POD_SQL_SERVER WHERE dpc_inuse_ind = 1 AND dpc_ismonitored_ind = 1 SET @totalrows = @@rowcount
The dpc_inuse_ind and dpc_ismonitored_ind flags allow instances to be excluded from monitoring in the event of maintenance. Setting @totalrows to the @@rowcount returned from the insert provides an upper limit for the loop that will run in the next step.
WHILE @currentrow <= @totalrows BEGIN SET @servername = (SELECT TOP 1 servername FROM #serverlist) SET @currentrow = @currentrow + 1 SET @sqlstr = @servername + + '...xp_cmdshell ''tasklist''' INSERT INTO #processes EXEC (@sqlstr) SELECT @rowcount = COUNT(*) FROM #processes WHERE processlist LIKE '%sqlagent%' INSERT INTO #status VALUES (SUBSTRING(@servername,4,8), @rowcount) DELETE FROM #serverlist WHERE servername = @servername DELETE FROM #processes END
The WHILE loop executes the code between the begin and end once for each row in the temp table, starting with @currentrow set to 1.
WHILE @currentrow <= @totalrows
The next two lines select the first instance out of the temp table, write it to variable @servername and increment the @currentrow counter.
SET @servername = (SELECT TOP 1 servername FROM #serverlist) SET @currentrow = @currentrow + 1
The next three lines build a dynamic SQL string using an xp_cmdshell command to generate a list of services running on the instance. This dynamic SQL string is executed and the results are inserted into temp table #processes.
SET @sqlstr = @servername + + '...xp_cmdshell ''tasklist''' INSERT INTO #processes EXEC (@sqlstr)
Next, variable @rowcount is populated with the count of SQL Agent processes running on the machine. A non-zero count indicates the process is running.
SELECT @rowcount = COUNT(*) FROM #processes WHERE processlist LIKE '%sqlagent%'
In order to prevent an alert when the instance is starting up, the create date for tempdb and the datetime value from 5 minutes earlier are captured.
SELECT @crdate = crdate FROM master.sys.sysdatabases WHERE name = 'tempdb' SELECT @startup = DATEADD(minute,-5,getdate())
If the rowcount is 0 and the instance has been up for more than 5 minutes, an e-mail will be sent indicating the instance SQL Agent is not running on the instance. The REPLACE statement strips the DUL prefix from the instance name.
IF (@rowcount = 0 AND (@sixmin > @crdate)) BEGIN DECLARE @body1 VARCHAR(100) DECLARE @subject1 VARCHAR(100) DECLARE @servermail VARCHAR(8) SET @servermail = REPLACE(@servername,'DUL','') SET @body1 = 'SQL Server Agent is Down on '+@servermail+ ' - Please Check' SET @subject1 = 'SQL Server Agent is Down on ' + @servermail EXEC msdb.dbo.sp_send_dbmail @recipients=henry@skreebydba.com', @profile_name = 'DBASQLServerPublicProfile', @subject = @subject1, @body = @body1, @body_format = 'HTML' ; END
The final code in the loop deletes the current instance name from the #serverlist table and clears out the #processes temp table.
DELETE FROM #serverlist WHERE servername = @servername DELETE FROM #processes END
Once the loop completes, the temp tables are cleaned up and the procedure finishes.
DROP TABLE #processes DROP TABLE #serverlist
The combination of dynamic SQL within a loop is an extremely powerful tool. This example provides a template we've used for many different tasks in the enviroment. I hope you can put these ideas to use.
USE [DUDMON] GO /****** Object: StoredProcedure [dbo].[DUP_CHECK_SQL_AGENT] Script Date: 03/06/2012 11:40:23 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE procedure [dbo].[DUP_CHECK_SQL_AGENT] as /* DUP_CHECK_SQL_AGENT – Checks to verify that SQL Server Agent is running on all of the PODS servers. Queries the sysprocesses table to see if the SQL Server Agent process is running. If it is not, an e-mail will be sent. Parameters: None Dependent procedures and Tables: None Created by - Frank Gill Last Updated by - Frank Gill Last Updated - 17 May 2010 Version - 1 */ SET NOCOUNT ON BEGIN TRY -- Declare local variables DECLARE @servername VARCHAR(40) DECLARE @sqlstr VARCHAR(2000) DECLARE @totalrows INT DECLARE @currentrow INT DECLARE @running INT DECLARE @rowcount TINYINT CREATE TABLE #processes (processlist VARCHAR(4000)) CREATE TABLE #serverlist (servername VARCHAR(40) not null) CREATE TABLE #status (linkedserver VARCHAR(8) ,[status] TINYINT) set @currentrow = 1 -- Build list of valid linked servers INSERT #serverlist SELECT 'DUL' + dpc_sql_cluster_nm FROM duddba_master.dbo.DUT_POD_SQL_SERVER WHERE dpc_inuse_ind = 1 AND dpc_ismonitored_ind = 1 SET @totalrows = @@rowcount -- Begin looping through the list of linked server values WHILE @currentrow <= @totalrows BEGIN --select @currentrow as CURRENTROW SET @servername = (SELECT TOP 1 servername FROM #serverlist) SET @currentrow = @currentrow + 1 SET @sqlstr = @servername + + '...xp_cmdshell ''tasklist''' SELECT @sqlstr INSERT INTO #processes EXEC (@sqlstr) SELECT @rowcount = COUNT(*) FROM #processes WHERE processlist LIKE '%sqlagent%' SELECT @crdate = crdate FROM master.sys.sysdatabases WHERE name = 'tempdb' SELECT @startup = DATEADD(minute,-5,getdate()) IF (@rowcount = 0 AND (@sixmin > @crdate)) BEGIN --SELECT @servername AS [Server name] --SELECT 'This stuff is broke!!!' DECLARE @body1 VARCHAR(100) DECLARE @subject1 VARCHAR(100) DECLARE @servermail VARCHAR(8) SET @servermail = REPLACE(@servername,'DUL','') SET @body1 = 'SQL Server Agent is Down on '+@servermail+ ' - Please Check' SET @subject1 = 'SQL Server Agent is Down on ' + @servermail EXEC msdb.dbo.sp_send_dbmail @recipients='fgill@allstate.com', @profile_name = 'DBASQLServerPublicProfile', @subject = @subject1, @body = @body1, @body_format = 'HTML' ; END DELETE FROM #serverlist WHERE servername = @servername DELETE FROM #processes END DROP TABLE #status DROP TABLE #processes DROP TABLE #serverlist END TRY BEGIN CATCH INSERT INTO dbo.DUT_ERROR_LOG SELECT @servername, @status, getdate(), CURRENT_USER AS CurrentUser, ERROR_NUMBER() AS ErrorNumber, ERROR_SEVERITY() AS ErrorSeverity, ERROR_STATE() AS ErrorState, ERROR_PROCEDURE() AS ErrorProcedure, ERROR_LINE() AS ErrorLine, ERROR_MESSAGE() AS ErrorMessage; END CATCH GO
Checking SQL Server Agent Status Using xp_cmdshell
I work in a clustered environment running more than 200 instances of SQL Server 2008. Several years ago, we began having problems with the SQL Server Agent service failing after an instance failed over. We had already developed a process to check the health of the SQL Server service, so I set out to add an Agent check to it.
Doing some web searching, I came across a number of links that suggested running the following query to determine if SQL Server Agent was running:
SELECT COUNT(*) FROM master.dbo.sysprocesses WHERE program_name = N'SQLAgent - Generic Refresher'
In the tests I ran, this worked just fine. I put it into a procedure, rolled it out to our test environment and let it run for a week, where we had no issues. It caught a number of times that the Agent was down and provided no false positives. At this point I rolled the proc out to production.
Several weeks later, we started receiving messages that the SQL Agent was down on an instance. Management Studio and Windows Failover Cluster Management showed the process was up and running. We were able to access Agent jobs and metadata, and jobs were running successfully. I queried the dbo.sysprocesses DMO on the instance and did not get a hit for 'SQL Agent - Generic Refresher'.
This led me to open a ticket with Microsoft to find out if they could tell me why there was no row in the sys.processes DMO when the process was running. If they couldn't do that, I was hoping they could tell me a better way to check status programmatically. I was told that querying the sys.processes table was not recommended and that they could not provide me with any other suggestions.
At that point, other things took precedence until two weeks ago, when we started receiving messages the Agent was down on an instance. Taking a look at the sys.processes table, there was no row for 'SQLAgent - Generic Refresher'.
The instance that was failing was excluded from the job and I worked on another method of checking the Agent service. Since the last time I looked at this issue, I gained experience using xp_cmdshell in T-SQL code. This led me to use the following command:
EXEC xp_cmdshell 'tasklist' GO
This code returns a list of all of the processes running on the machine. By inserting the results of this code into a temp table, you can run a select to check for the existence of the SQL Agent process. That code looks like this:
USE master GO CREATE TABLE #processes (processlist VARCHAR(4000)) INSERT INTO #processes EXEC xp_cmdshell 'tasklist' SELECT * FROM #processes WHERE processlist LIKE '%sqlagent%' DROP TABLE #processes
Here are the query results:
processlist |
SQLAGENT.EXE 9896 Services 0 38,316 K |
I've put that block of code into a procedure that loops through all of the instances in our environment checking the status of SQL Server Agent. If the check fails, an e-mail is sent out to the DBA team. I will cover this procedure in my next post.