Category Archives: System

How to determine why a T-SQL command is unreasonably slow

If you’ve ever found yourself in the situation were a command executing against a small table is nowhere near instant there can be numerous reasons for this but the most common causes are locks and waits.

The first step in identifying the problem is to execute the script below in a new query window while the troublesome command is running.

/* Queries Not Running */
SELECT ROW_NUMBER() OVER (
		ORDER BY r.total_elapsed_time DESC
		) AS Rn
	,st.TEXT AS SqlText
	,r.*
FROM sys.dm_exec_requests r
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS st
WHERE r.status <> 'running';

/* Queries Running */
SELECT ROW_NUMBER() OVER (
		ORDER BY r.total_elapsed_time DESC
		) AS Rn
	,st.TEXT AS SqlText
	,r.*
FROM sys.dm_exec_requests r
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS st
WHERE r.status = 'running';

 

This script will return two lists of the currently active sessions along with the stats associated with their execution. The first list will contain all the active sessions that are not running. The second list will contain all the active sessions that are running and will likely not contain the troublesome query you’re dealing with.

Identify your session based on the SqlText field. Be sure you’ve identified the session correctly as you may decide you want to kill the process later and killing the wrong one could cause you a lot of trouble.

  • status : If the status is not running look to the other fields in the returned result set to help identify the problem. If the session is in the running result set but you are unhappy with the performance it is likely the T-SQL needs to be optimized to make it run faster. This is a very broad topic and there are tons of articles and guides on the internet dealing with it.
  • blocking_session_id : If another session is blocking yours from executing, e.g. it has locked a table your command needs to write to, then this field will include the Id of the session causing the table to be locked. You can use EXEC sp_who2 to assess if the underlying command/query is experiencing a problem. If you are familiar with the blocking session you may know that you are able to kill the session without incurring any negative consequences. You can use the following code snippet to kill the blocking session.
    KILL blocking_session_id /*replace by the actual Id*/

    NOTE: Before you kill anything if it’s a command that has been running for a very long time it will likely take at least the same amount of time to roll back and unlock the table. You might be better off waiting for the session to finish on its own.

  • wait_type : If no blocking session is available, then the query is waiting for something, e.g. server resources etc. More details about wait types can be found HERE
  • wait_time : This stat value is measured in milliseconds. Short wait times are fine, specially in PAGEIOLATCH wait types (access to physical files) but longer wait times indicate a more serious problem.
  • last_wait_type : Indicates if the last wait type was different. This is quite helpful in analyzing if the query was blocked for the same reason before.

 

How to disable all enabled user job schedules in SQL Server with T-Sql

I’d really recommend not running the output of this script on a live environment! This is just a little something I whipped up to test on a development environment.

Running the below script will output the T-Sql required to disable all enabled job schedules on the SQL Server instance. Just copy the outputted text and paste into a new SSMS window and execute to disable the jobs.

SET NOCOUNT ON

DECLARE @Schedule TABLE (ScheduleId INT)
DECLARE @ScheduleId AS INT
DECLARE @Sql AS VARCHAR(MAX)

SET @ScheduleId = ''

INSERT INTO @Schedule (ScheduleId)
SELECT s.schedule_id
FROM msdb.dbo.sysschedules AS s
WHERE s.[enabled] = 1
	AND s.owner_sid <> 0x01
ORDER BY s.NAME ASC

WHILE @ScheduleId IS NOT NULL
BEGIN
	SET @ScheduleId = (
			SELECT MIN(ScheduleId)
			FROM @Schedule
			WHERE ScheduleId > @ScheduleId
			)
	SET @Sql = '
EXEC msdb.dbo.sp_update_schedule @schedule_id = ' + '''' + CONVERT(VARCHAR(5), @ScheduleId) + '''' + '
	,@enabled = 0; 
'

	PRINT @Sql
END

How to disable all enabled jobs in SQL Server with T-Sql where the job name contains specific keyword text

Running the below script will output the T-Sql required to disable all enabled jobs on the SQL Server instance where the job name contains a specific keyword. Just copy the outputted text and paste into a new SSMS window and execute to disable the jobs.

For example, if you change the text value ‘PLACEHOLDER’, for the variable @KeyWord, to ‘Backup’ then any job which has ‘Backup’ in its name will have T-Sql generated to disable it. You could change the PRINT to EXEC but I wouldn’t recommend it.

DECLARE @KeyWord AS VARCHAR(256)

SET @KeyWord = 'PLACEHOLDER'
SET NOCOUNT ON

DECLARE @Job TABLE (JobName SYSNAME)
DECLARE @JobName AS SYSNAME
DECLARE @Sql AS VARCHAR(MAX)

SET @JobName = ''

INSERT INTO @Job (JobName)
SELECT j.NAME
FROM msdb.dbo.sysjobs AS j
WHERE j.[enabled] = 1
	AND j.NAME LIKE '%' + @KeyWord + '%' 
ORDER BY j.NAME ASC

WHILE @JobName IS NOT NULL
BEGIN
	SET @JobName = (
			SELECT MIN(JobName)
			FROM @Job
			WHERE JobName > @JobName
			)
	SET @Sql = '
EXEC msdb.dbo.sp_update_job @job_name = ' + '''' + @JobName + '''' + '
	,@enabled = 0; 
'

	PRINT @Sql
END
Space Sniffer image showing how much space AVG Web Tuneup using

AVG Web Tuneup you jerk!

So I finally got bothered enough to find out what the hell was eating up all the space on my C drive. I had just assumed it was something to do with the enforced Windows 10 upgrade but it turns out it was the AVG Web Tuneup application writing to the AppData directory. (Sorry for blaming you Windows 10)

For anyone else experiencing low disk space that is going unnoticed by disk cleanup utilities it might be worth checking this out. I used the fantastic utility Space Sniffer. This utility doesn’t require an install, it’s super light and super quick and will visually display all the files and folders on the drive you choose to scan. (Tip: run as administrator so it doesn’t throw warnings about directories it doesn’t have access to)

Space Sniffer image showing how much space AVG Web Tuneup using

To access the AppData folder on Windows 10 go to start and type %AppData%.

To rectify  this specific problem caused by AVG Web Tuneup utility first uninstall it. If this doesn’t get rid of the folder then access the AppData folder and navigate to AppData\Local\Packages\windows_ie_ac_001\AC\AVG Web TuneUp and delete that damn directory.

So long AVG Web Tuneup you jerk!