Reading execution plans in SQL Server is just hard. There's a lot to learn and understand. I previously outlined the basics I use to get started when I'm looking at an execution plan for the first time. However, just those pointers are not enough. I want to explain a little further why and how those basic steps are how you get started reading execution plans. To begin with, instead of talking about the first operator, which I've detailed before, we'll talk about the highest cost operators. Highest Cost Operator Every execution plan within SQL Server includes what the optimizer has determined to be the estimated cost of each operation. All these estimated operator costs are tallied up, and that makes up the estimated cost of the whole execution plan. You…
The general idea for this question came from dba.stackexchange.com: could we, and if we can, how, get row counts after execution. I was intrigued with the idea, so I ran some tests and did a little digging. I boiled it all down in the answer at the link, but I figured I could share a little here as well. Properly Retrieve Row Counts After Execution The right way to do this is obvious and simple. Before you need it, set up an Extended Events session. Done. The only question is what goes into the Session. First blush, sql_batch_completed and/or rpc_completed. Both will return a rows affected value. Although, interestingly, the row_count value is documented as rows returned. However, it's both. But, if you really want to get picky, batches and…
I am very excited to announce that I will be taking my paid precon content "Tools for SQL Server Query Performance Tuning" and presenting it for free. This is all a part of a new initiative from Redgate Software called Community Circle. Read about that here. I'll be livestreaming the precon once a week on the Redgate Youtube. So, please tune in, every Tuesday at 13:00CDT. Or, you can watch the recordings of the livestream, which we'll host on Youtube, free, forever. Between classes, you can ask questions, make comments, and generally interact through a Discord server I've set up here. We'll be covering a whole slew of topics from Query Store to DMVs, SQL Server Management Studio to Extended Events, Execution Plans and more, lots more. Whether you watch…
Wouldn't it be great to be able to put together queries and waits at the same time? You all capture query metrics using some method. Most of us query sys.dm_os_wait_stats or sys.dm_db_wait_stats. Combining them is hard. You could query the wait stats. Store the results in a table variable. Run the query in question. Then query the wait stats again into a different table variable. Join the two table variables together to find the differences. Ta-da, you have query waits. Well. Probably. If you're the only one running queries on the system. Also, you're not seeing system waits or other noise caused by activity on the system. Or, we could put Extended Events to work. Queries and Waits Just like Profiler/Trace, you can capture stored procedures, batches, and individual statements…
Of all the things that Extended Events does, I've found the ability to quickly and easily gather a little bit of data and then use the Data Explorer window Live Data grouping to aggregate it to be one of the greatest. Sure, if we're talking about using Extended Events on a busy production server, this method probably isn't going to work well. There, you are going to be better off querying the XML (I know, I know, but I have ways to help there too). But in development, when doing testing and query tuning, the Live Data window is a gift of the gods on par with fire or beer (it's not as good as whiskey). Live Data Grouping Let's imagine a scenario like this. You're working on some query…
Extended Events can do things that simply are not possible with Profiler and another example comes from the stack of audit events that exist only in Extended Events. One of these is a set of expanded events for database auditing. Comparing the list of things exposed through Extended Events to those exposed through Trace/Profiler isn't entirely fair. All new functionality is only in Extended Events since Trace hasn't been updated since 2008. However, these events that you can use to audit your database, aren't new functionality, they're just new events for watching old functionality. The addition of new events is just one more reason why moving to use Extended Events is a must. Auditing Databases In this instance, when I say audit the database, what I mean is keep an…
The single most important thing to remember about Extended Events is that this functionality is not simply a replacement for Profiler/Trace, but a whole new tool with new functionality. My first example for functionality that you simply cannot get in Profiler/Trace is the ability to output to a Histogram. Profiler/Trace can output to a table or to a file. Extended Events can have a target that is a file, same as Profiler. However, you can also have a target: etw_classic_sync_targetevent_counterhistogrampair_matchingring_buffer Read about each of the types in the Microsoft documentation here. I'm going to focus for the moment on the histogram target because it lets you do some fun stuff and easily collect data that you simply can't collect using Profiler/Trace without hopping through a bunch of flaming hoops. Setting…
I've decided that, in fact, it is time to start moving people off the ancient technology, Profiler. Before, I always said, stay where you're comfortable. However, keeping people comfortable means that they're also going to keep promoting Profiler/Trace to new people on new platforms. That is a real problem. To fix the problem of old school, slow, inferior, methods of data collection, troubleshooting, and consuming metrics, we need to educate people. Extended Events are not simply a replacement for Trace. They're not simply another way to gather query metrics. No, in fact, this is a whole new tool, with new functionality and a very high level of support and engagement from Microsoft. Extended Events are where all new functionality since 2012 provides mechanisms for monitoring behavior. As technologists we should…
I wrote a short blog post about the misperception that Profiler was easier than Extended Events when it came to the core concept of "click, connect, BOOM, too much data". Go read it if you like, but I don't think it's actually an effective argument for how much easier Extended Events is than Profiler. Here, we're going to drill down on that concept in a real way. Let's start with a little clarification. I'm going to be a little lazy with my language. Trace is a scripted capture of events on a server. Profiler is a GUI for consuming a Trace, either live or from a file, and for creating Trace events. However, almost everyone refers to 'Profiler' when they mean either Trace or Profiler. I may do the same…
I know, I know, I'm on #teamexevents so I think that Extended Events can do no wrong, but let's address this thought that Profiler is easier. Now, if we're strictly talking knowledge, sure, if you've got a lot of experience with Profiler/Trace and very little with Extended Events, of course Profiler is easer. However, what I'm told is that Profiler doesn't require very much set up, while Extended Events does. That's just wrong, but let's put it to the test. The Test For the comparison, we're not going to do anything special with either tool. I'm just going to start collecting query data with the fewest possible clicks and/or key strokes. I'm going to use both tools short cuts to make this as fast as possible. The goal is, click,…