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Live Query Statistics in SQL Server 2016


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Problem

SQL Server 2016, which is at the time of writing is in preview release CTP 2.1, has a great new feature called Live Query Statistics. It allows you to view a live execution plan of an active query, which gives us a fantastic opportunity for troubleshooting and debugging. This tip will give an introduction to this exciting new feature.

Solution

Live Query Statistics is a feature introduced in SQL Server 2016. It provides you with a live execution plan which displays overall query progress and run-time execution statistics such as elapsed time, operator progress, number of rows processed and so on. It goes without saying that this feature will be an excellent addition in your toolkit for performance troubleshooting and for the debugging of queries.

SQL Server 2016 Live Query Statistics Test Environment

In order to have a query executing long enough to see something actually happening in the execution plan, I used alternative versions of some AdventureWorks tables. These tables are generated by a script created by Adam Machanic (blog | twitter), which can be downloaded here. The script basically generates a large product table with 25,200 products and a transaction table with over 31 million transactions. Executing those scripts will keep SQL Server occupied for a while.

I used the following test query, which takes over 4 minutes to execute on my system:

SELECT 
	 TransactionMonth	= FORMAT([TransactionDate],'yyyy-MM')
	,Color
	,Quantity			= SUM(Quantity)
	,ActualCost			= SUM(ActualCost)
FROM [dbo].[bigTransactionHistory]	t
JOIN [dbo].[bigProduct]				p ON t.ProductID = p.ProductID
GROUP BY FORMAT([TransactionDate],'yyyy-MM'), Color;

It returns the aggregated values for Quantity and ActualCost per product color on a monthly basis.

Using Live Query Statistics

To view Live Query Statistics in action, you can simply enable it for the current session in Management Studio by clicking on its icon in the tools menu.

Push the button

When you execute the query, an extra tab is added in the results pane holding the live execution plan.

Yet another tab

You can immediately tell the difference with a normal execution by the dotted lines, instead of the full arrows. As you can see in the screenshot, each operator has an indicator of how much work is already done and how much time it spent working. At the bottom, you also get an overall progress indicator.

You can see the number of rows processed when you open up the properties window of an operator. This window will constantly refresh when the query is running.

Actual number of rows

When the query is finished, the arrows return to normal and the plan resembles an estimated execution plan. Remark that actual rows are not being displayed as in an actual execution plan.

Execution is finished

This is how Live Query Statistics look in real-time:

Look at it flow!

You can also view a live execution plan through Activity Monitor, however the statistics profile infrastructure must already be enabled for the session, which is currently one of the biggest disadvantages of Live Query Statistics!

Activity Monitor

If it isnít, the option will be grayed out.

Activity Monitor with sad trombone

There are other options as well to enable Live Execution Plans on a query:

  • Before you start the query, run SET STATISTICS PROFILE ON or SET STATISTICS XML ON. With both statements, you will be able to view the Live Execution Plan through Activity Monitor, but you wonít see the live plan in the query window itself.
  • You can enable the query_post_execution_showplan extended event. Be aware that this is a server-wide setting that will enable Live Query Statistics on any session. This can have of course a serious performance impact.

Limitations of Live Query Statistics

There are currently a few limitations when working with Live Query Statistics:

  • Columnstore indexes are not supported
  • Memory-optimized tables are not supported
  • Natively compiled stored procedures are not supported

A Live Execution Plan is also just as good as the statistics of the underlying tables. If there are issues with those, these can be reflected in the plan. Letís illustrate with an example.

Using the following undocumented statement, we can trick SQL Server into thinking dbo.BigProduct has only 10 rows.

UPDATE STATISTICS [dbo].[bigProduct]
WITH ROWCOUNT = 10;

The optimizer will create a plan using an incorrect estimate. When we take a look at the Live Execution Plan, we can see that immediately after the query started running some of the arrows are already solid and some operators are already at 100%, although the query is still running.

Replaced NULL values

The index seek at the bottom keeps resetting and in real-time you can observe this behavior:

Something's broken...

You can read more about updating statistics using a specific row count in the blog post UPDATE STATISTICS undocumented options.

Conclusion

Live Query Statistics are a very useful new tool in the tool belt of the T-SQL developer. A live execution plan allows you to directly take a look how the query is executing and to find out where the bottlenecks are. There are currently some limitations, but hopefully they will be resolved in the future.

Next Steps
  • Try it out yourself! Use the query from this tip and start a session where Live Query Statistics are enabled. You of course need an instance with the SQL Server 2016 preview.
  • You can read the official documentation about Live Query Statistics here.
  • The following tip gives an overview of all the new features in SQL Server 2016 CTP2.
  • For more information, read these tips on SQL Server 2016.


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About the author
MSSQLTips author Koen Verbeeck Koen Verbeeck is a BI professional, specializing in the Microsoft BI stack with a particular love for SSIS.

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Tuesday, September 01, 2015 - 5:31:11 PM - Kevin M Back To Top

Hey Koen,

Thank you for looking in to that!  Well, here's to hoping Microsoft doesn't intentionally hobble the functionality for the sake of pushing an upgrade.

Great article, thank you for taking the time to write it in the first place and your quick follow up!

Kevin


Tuesday, September 01, 2015 - 5:00:23 AM - Koen Verbeeck Back To Top

Update: Live Query Statics work on SQL Server 2014 if you have SSMS 2016, but you need SP1 installed for SQL Server 2014.


Monday, August 31, 2015 - 3:28:31 PM - Koen Verbeeck Back To Top

Hi Kevin,

apparently it does work, according to this blog post:

http://sqlblog.com/blogs/rob_farley/archive/2015/08/31/live-query-statistics-in-sql-2014-not-just-sql-2016.aspx

 

I still can't get it to work. Maybe I have an out-of-date SSMS 2016 preview?


Friday, August 21, 2015 - 6:40:23 AM - Koen Verbeeck Back To Top

Hi Kevin,

I tested it out, even before my previous comment was approved :)

It doesn't work on SQL Server 2014. I connected with SSMS CTP2.2 to a machine where SQL 2014 was installed, but everything related to Live Query Statistics is immediatelyl greyed out.

It is a CTP release, so this might change in the future, but for now it doesn't work.

Regards,
Koen 


Friday, August 21, 2015 - 3:02:31 AM - Koen Verbeeck Back To Top

Hi Kevin,

that's a very good question. I'd have to test it, so I'll get back to you on that.

Koen


Wednesday, August 19, 2015 - 7:19:35 PM - Kevin M Back To Top

Hey Ken,

Thank you for the great post!  Do you know or have you been able to test if SSMS 2016 connected to a SQL 2014 database will be able to show live query statistics since it is hitting a DMV added in SQL 2014?


Thanks!


Wednesday, August 19, 2015 - 7:52:14 AM - Junior Galv„o - MVP Back To Top

Hi, Koen Verbeeck.

Great article, good job.

Best regards.


Wednesday, August 12, 2015 - 10:58:52 PM - manu Back To Top

This would definitely help while answering customer queries like "where exactly query is stuck":).  Thanks for sharing.

 


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