Monitoring When Databases Go Offline

Jason Brimhall shows how you can create an extended event to track whenever databases go offline:

The other day, I shared an article showing how to audit database offline events via the default trace. Today, I will show an easier method to both audit and monitor for offline events. What is the difference between audit and monitor? It largely depends on your implementation, but I generally consider an audit as something you do after the fact. Monitor is a little more proactive.

Hopefully, a database being taken offline is a known event and not a surprise. Occasionally there are gremlins, in the form of users with too many permissions, that tend to do very strange things to databases and database servers.

Click through for the script.

Finding Who Changed Auto-Tuning Settings On Azure SQL DB

Arun Sirpal shows us the extended event to watch to learn who changed that auto-tuning setting:

It is said to be safe, reliable and proven using complex algorithms and built-in intelligence where it can do the following (see this link for more details: https://docs.microsoft.com/en-us/azure/sql-database/sql-database-automatic-tuning)

  1. CREATE INDEX – identifies indexes that may improve performance of your workload, creates indexes, and automatically verifies that performance of queries has improved.
  2. DROP INDEX – identifies redundant and duplicate indexes daily, except for unique indexes, and indexes that were not used for a long time (>90 days). Please note that at this time the option is not compatible with applications using partition switching and index hints.
  3. FORCE LAST GOOD PLAN – identifies SQL queries using execution plan that is slower than the previous good plan, and queries using the last known good plan instead of the regressed plan.

Personally I don’t  enable the option where it is allowed a “free-for-all” when creating/dropping indexes and forcing certain query plans. I like controlling the change, especially for production databases. To force this concept I wanted to use Extended Events to know when / if someone changed my settings for automatic tuning against my database.

Click through for the script.

Learning Why A Plan Was Removed From Cache

Grant Fritchey shows us that there is some limited information to tell us why an execution plan was removed from cache:

You’ll note that the second statement in the sequence is “CREATE OR AL…” in the batch_text. That’s me modifying the procedure. The very next event is sp_cache_remove. It shows the remove_method as “Compplan Remove”. This the plan being removed in an automated way from cache. The next three events are all for query_cache_removal_statistics.

What are they?

These are the statement level statistical information being removed from the DMVs. That’s right, we can observe that information getting removed from the system along with the plan from cache.

Unless I’m missing something, it seems like this is more helpful for pedagogical reasons rather than auditing reasons—I’d be concerned that on a busy production system, we’d see too many messages to correlate things all that well.

Sorting And Aggregating Extended Events Results

Matthew McGiffen shows off some of the things you can do easily with Extended Events Profiler:

When I’m using Profiler to analyse performance issues I often save the results to a table, or upload a trace file into a table, so that I can analyse the data. Often this involves aggregating the values for particular queries so that I can see the most resource hungry.

This is by no means a difficult process, but with Extended Events (XE) it’s arguably even easier.

Click through for a demonstration.

Capturing Implicit Conversions With Extended Events

Grant Fritchey shows how easy it is to build an extended event which captures implicit conversions:

Built right into the Extended Events is an event that captures conversions that would affect execution plans, plan_affecting_convert. This event will show both CONVERT and CONVERT_IMPLICIT warnings that you would normally only see within an execution plan. You can capture this event with others. Capturing events together along with causality tracking makes it very easy to track queries that have the issue. Here’s one example of how you might capture implicit conversions along with the query:

This kind of event can make system-level performance tuning much easier.

Learn Extended Events With This Workbench

Phil Factor gives us a great walkthrough of Extended Events:

A lot of the information about the way that SQL Server is working that can only be provided by Extended Events (XEvents). It is such a versatile system that it can provide a lot more than would otherwise require SQL Trace. If done well, Extended Events are so economical to use that it takes very little CPU. For many tasks, it requires less effort on the part of the user than SQL Trace.

Extended Events (XEvents) aren’t particularly easy to use, and nothing that involves having to use XML is likely to be intuitive: In fact, many DBAs compare XML unfavourably in terms of its friendliness with a cornered rat. SSMS’s user-interface for Extended Events, thankfully, removes a lot of the bite. For the beginner to XEvents with a background in SQL, it is probably best to collect a few useful ‘recipes’ and grow from that point. Templates and snippets are invaluable.

Phil’s workbenches (especially those written with Robyn Page) are fantastic ways of digging into a topic of interest.

Customizing Live Extended Events Data

Grant Fritchey shows how to make the Extended Events UI a lot more useful:

WHAT!!!!?!!

You mean I can make that upper window useful? Yes. Not only that, but, what ever columns you add to the upper window, your copy of Management Studio remembers what you did. The next time you open this Extended Events session in the the Live Data window, the columns you selected will be there. However, your ability to customize Live Data is even easier than that. If you notice, in the upper part of your SSMS window is the Live Data tool bar. Near the end is a button innocuously titled “Choose Columns.” Click on that and a window similar to this will open:

And you can share the results with others.

Read Event Stream Function Missing When Viewing Extended Events File

Tibor Karaszi points out an annoying bug which can happen when viewing an Extended Events file:

Here’s the relevant text in the message box, to facilitate searching:

The storage failed to initialize using the provided parameters. (Microsoft.SqlServer.XEventStorage)

Cannot view the function ‘fn_MSXe_read_event_stream’, because it does not exist or you do not have permission. (Microsoft SQL Server, Error: 15151)

Read on for the solution, and if you’re interested in changing that behavior, vote up the UserVoice submission.

Quick Tips For Working With Extended Events

Tibor Karaszi argues that it’s never too late to get into Extended Events:

I know, I know. New habits are hard to learn. Many of us have been using SQL trace and the Profiler GUI for a very long time. And we know that we are supposed to move over to Extended Events (XE), but we postpone it for some later time. And then we give XE a try, and some thing doesn’t work as we want. So we go back to more familiar territories.

But XE has really grown on me over the last few years. I like to share the things that I initially didn’t like with XE, and how I overcame them. And also some other of my tips to make it easier to be productive with XE. I will deliberately minimize showing T-SQL and queries against the XE dynamic management views here. As you use XE more and more, you will probably use T-SQL to a higher degree. But this blog post is for those of you who want to “get into” XE and I find using a GUI is great as a starting point. Assuming the GUI is any good, that is. And I think the SSMS GUI is, for most parts.

There are a lot of tips here, so check out Tibor’s advice.

Saving Extended Event Session Data To A Table

Matthew McGiffen shows how you can take the results of an Extended Events session and insert them into a table:

You just need to select a destination database connection and table name and the export starts. Be warned that it doesn’t default to the current database connection. I’ve fallen for that and overwritten the data in a table with the same filename on a different SQL instance – whoops!

If the option is greyed out when you open the menu it may be that your event data is still loading. If you look closely in the above screenshot you can see I have over 8 million events captured by this session, so it took a while to load before I was able to export.

There are a few gotchas that Matthew shows, but it’s a useful technique.

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