T-SQL Tuesday #67 – Extended Events for DBCC

tsqltuesdayIt’s the second Tuesday of the month and time for another T-SQL Tuesday. This time it’s #67 from Jes Borland on Extended Events. You can read the invite, and whether you can participate today or not, write your blog and leave a comment for Jes on her blog.

If you want to see all the topics from the past, I have them on a post here.

If you want to host, contact the founder of T-SQL Tuesday, Adam Machanic. He chooses the hosts and is always looking for people that want to participate. You just need a blog and a good idea.

Who Ran DBCC?

I ran across a question recently from someone that said DBCC messages had appeared in the error log, but no one had run DBCC. That’s not possible as DBCC isn’t run without someone, whether that’s a human or a service, executing the DBCC command.

In the past, I might recommend a trace to track this, but not I’d choose an Extended Events (XE) session. I’ll show how to set up a simple session, though be aware I’m not an XE guru. I’m sure there are better ways to structure this, but it worked well for me.

You can start quickly building a specific XE session by right clicking the Sessions folder under Extended Events in SSMS under Management. I tend to pick the wizard for getting started, though be sure to save the script later.

2015-06-08 11_36_10-SQLQuery2.sql - JOLLYGREENGIANT_SQL2012.Sandbox (JOLLYGREENGIANT_sjones (86))_ -

From here we get the opening screen for XE, which I won’t show. The next screen asks for a name for the session. It doesn’t matter, but once you start using XE, you’ll start to get quite a few session, so it’s handy to pick something that’s simple and easy to understand later.

2015-06-08 11_38_23-New Session Wizard_ Set Session Properties

I can choose to start the session here when I’m done, but don’t worry if you’re not sure. You’ll get a chance again later.

The next step is to decide whether you use a template or build a session from scratch. I’m not sure if any of these templates will work well as I haven’t dug in. In my case, I decided to just choose a generic session.

2015-06-08 11_41_07-New Session Wizard_ Choose Template

Now I need to pick the events. There are a lot, but I went down to get the sql_statement_completed as my event. This will let me see the text of a call, which is what I need.

2015-06-08 11_41_32-New Session Wizard_ Select Events To Capture

A couple notes here. One, you might want to grow this screen so that you can read what’s in the lower windows. I know there’s a lot of data here, but this screen doesn’t seem well defined.

The second note is that don’t forget to add the event with the arrow button. Until you have an event (or multiple events) in the right window, you can’t click "Next".

The next step is to get the data fields you need. Again, there are a lot, and I limited this to what I needed. I grabbed the client host and app, as well as the database. Then I grabbed the service_principal_name and sql_text as well. This should let me determine who’s running the command.

2015-06-08 11_45_29-New Session Wizard_ Capture Global Fields

I’ve got lots of data here, but I only care about the execution of dbcc checkdb. This means I need to filter things, which is my choice with the next screen.


Here I need to click in the top line to get a place to add a filter. Then I select sql_text from the drop down and choose like for the operator and "dbcc checkdb" for the value. This should grab events that execute with a dbcc call.

2015-06-08 11_49_19-New Session Wizard_ Specify Session Data Storage

I have to choose where to store this data. Since this is mostly a check for me, I can just use the ring buffer and keep data in memory. I lowered this to 10 events, but you can certainly pick what works for you. If you care about auditing, drop this in a file. For a small session like this, there’s not much data that’s going to be captured.

I get a summary screen, which lets me review settings. I haven’t shown it here, but once I pass that, I get the "Success" screen. This is where I can start the session, and actually watch live data if I want.

2015-06-08 11_51_20-New Session Wizard_ Create Event Session

For this, I’ll watch the live data.

2015-06-08 11_52_20-JOLLYGREENGIANT_SQL2012 - dbcc checkdb_ Live Data - Microsoft SQL Server Managem

I decided to test this first and see if it captures anything else. I ran a few queries, and then this:

2015-06-08 11_52_30-SQLQuery3.sql - JOLLYGREENGIANT_SQL2012.AdventureWorks2012 (JOLLYGREENGIANT_sjon

Still a blank, live data screen. Then I ran checkdb. I saw the results, and then ran it a few more times.

2015-06-08 12_23_59-JOLLYGREENGIANT_SQL2012 - DBCC execution_ Live Data - Microsoft SQL Server Manag

As you can see, I now can see that I ran checkdb against the EncryptionPrimer database.

This lets me do some quick auditing of what’s happening with my DBCCs. A smart DBA might even use this to ensure that DBCC is being run against some databases, perhaps on a spare machine.

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