Using the appropriate data type to avoid conversions or implicit conversions is a fundamental approach to good T-SQL coding practices. Implicit conversions can lead to poor performance. However, other than looking at every execution plan in your system, is there a way to see if you are experiencing implicit conversions? Actually, yeah, it's right there in Extended Events. plan_affecting_convert 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…
One complaint I've received frequently is that you can't see stored procedure parameter values in Extended Events. That is patently not true. However, it does depend on where and how you capture the events and which stored procedure parameter values you're going for. I think this is a holdover from 2008 when Extended Events... well, let's be kind and say... didn't work well. Now, they do. Let's explore this a little. Capturing Stored Procedure Executions As with most things, there's more than one way to capture stored procedure execution in Extended Events. First up, it depends entirely on how they're called and on your intentions when you capture the information. Here are the three methods I know to capture just the completion metrics on stored procedure calls: rpc_completed sql_batch_completed module_end…
There are so many reasons to love Extended Events that it can really be overwhelming, but, one more reason that I love them are the ability to customize Live Data. More importantly, you can share that customization with others or move it between machines. Let's explore this. Customize Live Data If you open up an Extended Events file, or connect to a running Session, you're looking at the Live Data window and it looks something like this: I won't lie, that's a pretty ugly UI. At the top are all the events you've captured. At the bottom are the event fields. If you want to look at the information in different events, you click on the event, then down at the fields... blech! However, I have some options. Let's right…
I advocate for, use, document, teach, and just downright love, Extended Events. They are so much better than the old Trace Events (aka, Profiler) that it's sometimes difficult to keep from just gushing. Let's talk about a common situation that you're going to run into on your servers all the time and how you can put Extended Events to work to help you, without actually doing any work at all. What's that? Be lazy and get rewards? Yes. The Extended Events system_health Session On your servers, any of them that are SQL Server 2008 or newer, right now, unless you've performed actions to prevent this, you're running the Extended Events system_health session. It's just happening, currently, on all your servers. Nothing you need to do about it at all. I'll…
I use Extended Events almost exclusively for capturing query metrics. They are the most consistent and lowest cost mechanism for getting the time and resources used by a query. They can be filtered, combined with other events, they're just marvelous... until you capture an execution plan. Execution Plans in Extended Events Don't get me wrong. Capturing execution plans with Extended Events is the way to go if you're attempting to automate the process of capturing plans on specific queries on an active system. It's step two that bugs me. So, we capture the plan. Here's an example script. Captures all the various plans and the batch, puts 'em together using causality tracking: CREATE EVENT SESSION ExecutionPlansOnAdventureWorks2014 ON SERVER ADD EVENT sqlserver.query_post_compilation_showplan (WHERE ( sqlserver.database_name = N'AdventureWorks2014')), ADD EVENT sqlserver.query_post_execution_showplan (WHERE…
Query tuning ain't easy. Figuring out which index is getting used is one step, and generally simple, look at the execution plan to see which index is in use and whether it's being used in a SEEK or a SCAN. Done. However, when your index isn't being used, how do you tell how or why something else is being done? Well, that's largely down to row counts which brings us to statistics. Which Statistics are Used Years ago I was of the opinion that it wasn't really possible to see the statistics used in the generation of a query plan. If you read the comments here, I was corrected of that notion. However, I've never been a fan of using undocumented trace flags. Yeah, super heroes like Fabiano Amorim and…
I know. You love Profiler. I hear you. You're wrong, but that's OK. Kidding... mostly. Unfortunately though, I think a lot of what passes for issues and problems with Extended Events is actually a lack of knowledge about how they work. Let's take an example and run with it. No Grid in Extended Events One of the pushbacks I hear about using Extended Events is that the Live Data GUI just doesn't have that neat Profiler grid output. Instead you see a list of events in the top pane and then you have to look at the details in the bottom pane. It looks like this out of the gate: You're right. That's a royal pain. That's it. Toss Extended Events. Back to Profiler. Well, hang on a second. Let's…
There's a war on in the SQL Server world. On the one side is Profiler (although, really, everyone uses Trace Events). On the other, the "new" (they came out in 2008 with a full GUI in 2012, so...) Extended Events. Lots of people have picked sides on this, including Microsoft. New Trace Events There are none. All the new functionality of every sort from Availability Groups to Query Store to R & Python, have Extended Events created for them. Trace Events, and the technologies supporting them in the form of Profiler, are a dead end. Don't fear. While Trace is on the deprecation list, there doesn't appear to be any fear of that technology being removed completely. At least it won't be removed in the foreseeable future. A future which,…
I’ve been working quite a bit over the last week or so with extended events in Denali. The sheer magnitude of what you can do with extended events is just becoming clear to me. The interesting thing though is how much the basics are similar to trace. Similar mind you, not the same. For example, the best way to gather trace data is to output it to a file and then read the file into a table for later querying. It’s the same with extended events. There’s even a function that acts as a table: SELECT * FROM sys.fn_xe_file_target_read_file ('C:\APath\Query Performance Tuning*.xel', NULL, NULL, NULL); This can take advantage of roll-over files just like the old function used for traces. You can also provide offsets to read a sub-set of…
I’m working on updating my book, Query Performance Tuning Distilled, so that it reflects the new things available in SQL Server vNext:Denali. I’m going through the first chapters that are all about gathering information about your systems. Performance tuning is all about building up knowledge of how the system is working in order to understand what you need to change in order to improve it. I’m surprised by how much hasn’t changed. But some of the changes are fundamental and huge. Let’s talk huge. Extended Events is huge. Extended Events came out in SQL Server 2008, but very few people, myself included, paid much attention. Those who did found the implementation awkward and confusing. Only a few people persevered enough to discover just how powerful and amazing these things are.…