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Category: Query Store

Finding Query Performance Issues with Query Store

Andrea Allred has a primer on Query Store:

So if I can’t modify or add indexes and I can’t change code, how do I get my query times to drop? Query Store to the rescue.

I love to tune queries. I feel so satisfied to see the times dropping on my server as I tune things. Recently, I have been tracking my Batch Requests per Second and my Instance Waits to see if I am making improvements when I tune. It has been awesome!

What I am going to show you today is how I dig into my query store to find those misbehaving queries and make their performance better.

Click through for some high-level tips on how to use Query Store.

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Using Query Store to Track Regressions after Upgrades

Grant Fritchey has another use for Query Store:

There are a lot of uses for Query Store, but one of the most interesting is as an upgrade tool. We all know that upgrades in SQL Server can be more than a little bit nerve wracking. No matter how much you tested stuff in lower environments, deploying an update to production might result in performance issues as your code hits a regression. This is even more true when upgrading from versions of SQL Server prior to 2014 to anything 2014 and above. That’s because of the new cardinality estimation engine introduced in 2014. Most queries won’t notice it. Some queries will benefit from the better estimates. A few, problematic, queries will suffer. This is where Query Store can be used as an upgrade tool.

Read on to learn how.

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Query Store and Cross-Database Queries

Matthew McGiffen does some research:

When I was writing the script shared in my last post Identify the (Top 20) most expensive queries across your SQL Server using Query Store a question crossed my mind:

Query Store is a configuration that is enabled per database, and the plans and stats for queries executed in that database are stored in the database itself. So what does query store do when a query spans more than one database?

Read on for the answer.

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Identifying Expensive Queries with Query Store

Matthew McGiffen has a query for us:

Some time ago I wrote a query store version of the “Top 20 queries” query that will produce a ranked list of your most expensive queries – and I’ve ended up using this a lot.

The only downside of using the DMVs for Query Store is that they are per database whereas dm_exec_query_stats is a view across the whole instance. So I had to use a cursor and a temp table, populating the temp table for each database in turn.

Click through for the query.

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Query Store Checks in dbatools

Jess Pomfret contributes to dbatools:

Once I was happy with my settings, I realised we were missing a ‘test’ command for dbatools. The suite of ‘test’ functions in dbatools (a lot that end up as checks in dbachecks btw!), give us an easy way to check our environment against best practices, or our desired settings.

Since dbatools is open-source I was able to write this function (Test-DbaDbQueryStore) and get it added into the module. It’s included as of version 1.0.131, so make sure you’re up to date.  Taking Erin’s suggestions and wrapping them in a little PowerShell, I can make it easier for myself and everyone else to make sure we’re following her guidelines.

Click through to see what those settings look like and how you can compare against current settings.

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The Performance Overhead for Query Store

Erin Stellato updates a prior post:

I wrote the original Query Store performance overhead post just over two years ago, and just like the data in your database keeps changing, so does SQL Server.  However, the question, “What is the performance overhead of enabling Query Store?” is still the most frequent question I am asked. 

So why am I writing this post?  Because there have been many improvements specific to Query Store that have taken the feature to the point where it can support all workloads, including those that are ad-hoc.  This is a big deal.

Read on to learn more.

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The Big Red Button for Query Store

Erin Stellato shows us the emergency off switch for Query Store:

Have you ever tried to turn off Query Store when there was an issue, and you thought the problem might be related to Query Store, and the ALTER DATABASE statement was blocked?  And then you couldn’t do anything but wait?  Me too.  Imagine my excitement when I discovered that the SQL Server team snuck a helpful back door into ALL versions for which Query Store is supported. 

Read on for more, including which SP / CU levels support it.

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Using Query Store over the Plan Cache

Erik Darling has a dream:

I used to think the plan cache was so cool.

– You can find queries that aren’t good there
– Plans are full of details (and XML)
– Supporting DMVs give you extra insights about resource usage

But most of the time now, I’m totally frustrated with it.

It clears out a lot, plans aren’t there for some queries, and the plans that are there can be very misleading.

Can you really tell someone what their worst performing queries are when everything in there is from the last 15 minutes?

No.

Read on for what’s nice about Query Store, as well as a few fixes which need to be there before it’s really useful. I’ve used Query Store in big environments to good effect (though our DBAs had to rewrite the cleanup processes because they’re bad) and I’ve had to turn it off in medium-sized environments running 2016 because it was harming performance. It’s a great concept and reasonable implementation with a few too many sharp edges.

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