Can You Force A Parallel Plan in Query Store?

SQL Server 2016, SQL Server 2017
I love the questions I get when presenting: Can You Force a Parallel Plan in Query Store. I haven't a clue. The trick I think is going to be in setting up the test. Let's try it out. Reliably Getting a Parallel Plan Because this is for testing, rather than try to build some crazy query that may or may not go parallel, I've decided to cheat. I'll take advantage of a little functionality that ensures I see a parallel plan when I want to. Here's my code: DBCC TRACEON(8649); GO SELECT soh.OrderDate, soh.ShipDate, sod.OrderQty FROM Sales.SalesOrderHeader AS soh JOIN Sales.SalesOrderDetail AS sod ON sod.SalesOrderID = soh.SalesOrderID WHERE soh.SalesOrderID = 43705; GO DBCC TRACEOFF(8649); Traceflag 8649 will force all plans to go parallel by effectively making the Cost Threshold for…
Read More

Missing Indexes in the Query Store

SQL Server 2016, SQL Server 2017, T-SQL, Tools
I've shown before how to use the DMVs that read the plan cache as a way to connect the missing indexes suggestions with specific queries, but the other place to find missing index suggestions is the Query Store. Pulling from the Query Store The plans stored in the Query Store are exactly the same as the plans stored within the plan cache. This means that the XML is available and you can try to retrieve information from it directly, just as we did with the missing index queries against the DMVs. Here's the query modified for the Query Store: [crayon-5cdeeaaeebbf9495281672/] A couple of notes on the query. I cast the query_plan as xml so that I can use the XQuery to pull out the information. It is possible that the…
Read More

How Do You Export A Database in Azure Data Studio

SQL Server, SQL Server 2016, SQL Server 2017
I've been writing a bunch about Azure Data Studio. I've also been recording videos on the topic. A comment I received recently asked how to export a database from Azure Data Studio. It made me want to explore the topic of exporting a database as it relates to Azure Data Studio. Export? When we say export, what exactly do we mean. It could be as simple as exporting data to a flat file for consumption in Excel or something. It could be creating a backup. Maybe we mean creating a bacpac file. We could also be looking at creating individual scripts for objects within the database. Finally, what about a full export of the database object definitions? Any or all of these could be what the question was about. So,…
Read More

Installing Extensions to Azure Data Studio

Azure, SQL Server 2016, SQL Server 2017, T-SQL
If you're even thinking about experimenting with, let alone actively using, Azure Data Studio, you need to plan on installing a few extensions. Buck Woody has a great list that you should look through in this blog post. If you're just getting started with Azure Data Studio, I have an introduction here. Depending on the extension, this could be a simple as a mouse click. However, not all the extensions are that easy. Let's explore this just a little so when you do start using Azure Data Studio, things are easy. Extension From a Mouse Click For this bit of the blog post, we'll stick to nothing but mouse clicks, but, if you really want to bring the power within Azure Data Studio, you really need to learn keyboard shortcuts…
Read More

Combine Extended Events and TagWith to Monitor Entity Framework

SQL Server 2016, SQL Server 2017, T-SQL
I'm going to start with a sentence that makes a lot of people crazy; As a DBA and database developer, I love Entity Framework. That's right. Entity Framework is the bomb. It's amazing. It does wonderful stuff. Entity Framework makes the developers lives and jobs easier. It makes my life and job easier. Yes, Entity Framework will improve your job quality and reduce stress in your life. With one caveat, it gets used correctly. That's the hard part right? There is tons of technology that makes things better, if used correctly. There are all sorts of programs that make your life easier, if used correctly. Yet, all of these, used incorrectly, can make your life a hell. One nit that I've always had with Entity Framework is that it's very…
Read More

All Day, Training Day at SQLBits

Azure, SQL Server 2016, SQL Server 2017, T-SQL
It's a somewhat late addition, but I have an all-day Training Day at SQLBits. It takes place on Thursday, February 28th. You can read all about it on the SQLBits web site. I want to take a moment here to expand on the information that we're going to cover. I think the abstract does a good job of conveying what we'll be doing all day, but I figured a little more detail won't hurt. Query Tuning is Hard This is the very first thing I talk about. Query tuning is hard. I've got a nearly 1,000 page book on the topic, which should give you an idea of just how much material there is to cover. With the training day I've decided to focus on the tools that Microsoft gives…
Read More

Forcing a Plan That Has a Plan Guide

SQL Server 2016, SQL Server 2017, T-SQL
The question that came up during a recent class I was teaching was: What if you have a plan guide to get the plan you want, but then decide, instead of using the plan guide, you'll just force the plan? Ummmm…. No idea. Let's test it. First, Create a Plan Guide I have a couple of queries I use to teach about how statistics affects plan choice, so we'll use that here. I'm going to also define and create a plan guide that makes this plan use a small row count for all queries against it: [crayon-5cdeeaaeedc8c677375222/] This is a really straight forward example of a plan guide. The only thing of note is that you should see that I have formatted my @stmt value exactly the same as what…
Read More

Query Store and Plan Cache Plans Compared

SQL Server 2016, SQL Server 2017
Query Store plans and the plans in cache are identical, right? There won't be differences because the plan that is in cache is the plan that was used to execute the query. Similarly, the plan that is in the Query Store is the plan that was used to execute the query as well. Therefore, they will be the same. However, some small differences actually can show up. Differences Between Plans In order to compare the two plans, first, we need a query. Here's a stored procedure that I'm going to use to generate a plan that will be in cache and in the query store: [crayon-5cdeeaaeeebbe517799110/] Nothing to it really. What I'm going to do is execute the query. That will load it into the cache and into query store.…
Read More

Explicitly Drop Temporary Tables Or Wait For Cleanup?

SQL Server, SQL Server 2016, SQL Server 2017, T-SQL
I was recently asked if we are going to see performance differences if we explicitly drop temporary tables. I couldn't remember the specifics, but I said it actually didn't matter. However, that answer has bugged me, so I set up a quick test. Explicitly Drop Temporary Tables We could make this a crazy set of tests, but I wanted to keep things relatively simple. I created two procedures that create identical temporary tables. One drops the tables, the other doesn't: [crayon-5cdeeaaeef2cc411933173/] I then set up Extended Events to capture the query metrics and I executed each of the queries multiple times (also, just for the test, I discarded the results because I didn't want that process mucking with my measurements). After executing both procedures 500 times, the results were quite…
Read More

Why Did a Plan Get Removed From Cache?

SQL Server, SQL Server 2016, SQL Server 2017, T-SQL
I was recently asked if we could tell why a plan was removed from cache. If you read this blog, you know what I'm going to say next. I checked the extended events and there are actually two different events that will tell us information about a plan removed from cache; sp_cache_remove and query_cache_removal_statistics. Let's talk about how these work. Removed From Cache Just so we can see ALL the activity, I'm creating an Extended Events session that captures a little more than just the two events: [crayon-5cdeeaaef0491963359683/] I'm capturing batch start and complete, rpc start and complete, and finally all the cache statements, hit, miss, insert and remove. The first time I run a procedure, the results could look like this: Since this is the first time running the…
Read More