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Category: Extended Events

Antipattern Queries Extended Event in SQL Server

Published 2023-02-06 by Kevin Feasel

Bob Ward enumerates some anti-patterns SQL Server can guilt you over:

If a query uses certain antipatterns, it will be detected during query optimization.  For both SQL Server and Azure SQL (internally on by default), if these antipatterns are detected when optimizing the query, and the query_antipattern event has been added as part of a running extended event session, the output will be captured.  The output will contain the relevant capture fields configured for the extended event session, allowing one to quickly identify which queries contain these antipatterns and are, therefore, prime candidates for tuning.

Read on for more information about this extended event, which is new to SQL Server 2022. I haven’t used this yet, so the two caveats I’m about to give are speculative in nature…though when has that ever stopped me? Caveat the first: just because something shows up as an anti-pattern doesn’t mean it needs to be fixed. There can be good reasons why you have chosen what is normally a less-efficient path. Caveat the second: just because something doesn’t show up as an anti-pattern doesn’t mean it’s fine. These are likely directional and my guess is that SQL Server will be fairly conservative in its estimation of what constitutes an anti-pattern so that you don’t get a lot of false positives.

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Finding a Scalar Function Caller

Published 2023-01-23 by Kevin Feasel

Matthew McGiffen searches for the root of the problem:

In this post we look at a method using Extended Events (XE) to identify what parent objects are calling a given SQL function and how often.

The background is that I was working with a team where we identified that a certain scalar function was being executed billions of time a day and – although lightweight for a single execution – overall it was consuming significant CPU on the server. We discussed a way of improving things but it required changing the code that called it. The problem was that the function was used in about 700 different places across the database code – both in stored procedures and views – though the views themselves would then be referenced by other stored procedures. Rather than update all the code they’d like to target the objects first that execute the function the most times.

Read on to see how Matthew did it, as well as some caveats along the way.

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Tracking Database Errors with Extended Events

Published 2022-12-07 by Kevin Feasel

Eitan Blumin is watching you:

But interestingly enough – we would be getting an added benefit here. Even if there is no SQL injection attack, it’s still possible that such errors would be raised by the application – simply due to bugs.

Furthermore, these errors in the database may be happening without anyone even noticing! How could that be, you ask? Well, it could be due to bad error handling that “swallows” the error entirely, or because the errors are logged but no one is bothering to look at the logs, or maybe because the errors are caught but an undetailed error message is logged/displayed to the user (I can’t even count how many times I encountered “general database error” messages in applications), or because the developers simply decided to mark this as a “known issue” that they didn’t bother to fix and they didn’t think to ask their DBA about it… The reasons are numerous and varying.

Click through for the scripts. I had built something similar about a decade ago, a simple WPF app which watched for errors. I messaged him with something like “You missed a comma in that IN clause” and I saw him pop up from his cubicle and look around, trying to figure out how I could peek over his shoulder and see the query.

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Where Extended Events Go by Default

Published 2022-12-01 by Kevin Feasel

Tom Zika is curious:

Have you ever wondered where the .xel file is saved when you create a new Extended Event session and don’t specify the full path (just the file name)?

Like so: [image removed because you should go to Tom’s site and see it, ed.]

Well, so did I and here’s what I’ve found out.

Click through to learn where these files end up if you don’t specify anything.

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Extended Event Performance Metrics in SQL Server 2022

Published 2022-11-29 by Kevin Feasel

Mitchell Sternke looks at some new extended events:

Running Extended Event (XEvent) sessions on SQL Server has a cost. Since XEvents was designed for high-performance, this is usually unnoticeable. However, it can become an issue depending on which events, actions, and other XEvent features are in use. New metrics available in SQL Server 2022, in Azure SQL Database, and in Azure SQL Managed Instance can help you understand the performance impact of using XEvents in your database.

The sys.dm_xe_session_events DMV (sys.dm_xe_ database_session_events on Azure SQL Database) provides one row for each event found in an active session definition, allowing you to see all events that are currently publishing on your SQL Server instance. Four new columns have been added to help with troubleshooting performance:

Read on to learn more about these columns and what they can do for you.

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Extended Event Duration Filtering and Looping

Published 2022-10-20 by Kevin Feasel

Erik Darling notes a problem with time-based filters on operations:

There are six waitfor commands that each pause for 1 second. In between them are queries that finish in milliseconds.

If I watch the event output, eventually, I’ll see this:

Okay, so the stored procedure took more than 5 seconds, but… no individual query took more than 5 seconds.

This happens a lot and I’m not sure there’s a good answer for it.

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Tracking Power BI Desktop Activity in SQL Server

Published 2022-10-06 by Kevin Feasel

Chris Webb looks in on things:

Something I do all the time when performance tuning Power BI is use SQL Server Profiler to monitor query and refresh activity. There’s a handy external tool that lets you open up Profiler with a connection to Power BI Desktop; if you’re using Power BI Premium you can also connect Profiler up to a published dataset using the XMLA Endpoint. Profiler is a bit old-school though and likely to lead to snarky comments from SQL Server DBAs (it’s not deprecated for Analysis Services though!) who’ll say you should be using Extended Events (aka xEvents) instead. And guess what – did you know you can use Analysis Services xEvents to monitor activity in Power BI Desktop?

It’s the power of Extended Events.

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Tracking Bulk Insert Usage with Extended Events

Published 2022-09-30 by Kevin Feasel

Grant Fritchey wants to see if you’re bulking up:

Wouldn’t it be great to be able to directly monitor specific behaviors within SQL Server, like, oh, I don’t know, knowing exactly when, and how, someone is using BULK INSERT? Well, you can, thanks to Extended Events through the bulk_insert_usage event.

Click through for an overview of what this event provides, as well as what it doesn’t provide.

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