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Category: Query Store

Adoption Patterns with Query Store

Published 2020-03-11 by Kevin Feasel

Erin Stellato has some thoughts on Query Store adoption:

Last fall we had a previous customer reach out for help after they had to wait 45 minutes for a database to come online after a server reboot. The database queries were blocked by QDS_LOADDB waits. There were three things in play here – the first was that they had CAPTURE_MODE set to ALL, and it should be AUTO. Second, they didn’t have trace flag 7752 enabled (the behavior of which is now the default in SQL Server 2019). And the third was that their Query Store was 100GB in size. The workload was fairly ad hoc, so these three things together caused the problem initially described. They implemented the TF, made multiple changes to the settings (set CAPTURE_MODE to AUTO, changed MAX_STORAGE_SIZE_MB to 10GB, decreased CLEANUP_POLICY to 3 days), and then Query Store was usable for them.

Read on for more examples.

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Query Store and Spinlocks

Published 2020-03-11 by Kevin Feasel

David Fowler takes a look at an issue with Query Store:

We moseyed on down to the server in question to take a look at it.  One thing stood out immediately, CPU was pegged out at 100% but SQL itself didn’t actually seem to be doing anything, transactionssecond was on the floor. Unfortunately this happened a while back and I didn’t think to capture any graphs or metrics at the time so you’re just going to have to take my word for this.

After looking into a few different things, the mention of spinlock contention came up.  I’ll be honest here, actual spinlock contention is rare and is something that I’ve seen cause an issue only a handful of times so it’s something that I don’t generally get to until I’ve ruled out just about everything else.

David’s scenario was on an older patch of SQL Server and it was fixed later. It’s a good reminder to keep those servers patched.

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Finding Query Store’s Server Impact

Published 2020-03-11 by Kevin Feasel

Tracy Boggiano shows us how to track the performance impact of Query Store on an environment:

This month’s T-SQL Tuesday blogging party is brought to you well by me and I wanted to talk more about Query Store.  I did write a book on it but there if still more to know about that is not in the book.  I am sure the rest of everyone’s posts will prove enlightening and provide valuable content for folks using or looking to implement Query Store.  Someone should have told Grant to hold off a week on his post about DROP / CREATE of procedures and what happens with plan forcing so it could officially be part of the party.

I frequently get asked while presenting about the impact of running Query Store on the instance and one thing that was not in the book was the performance counters that were added to help track just that.

You should probably buy a bunch of copies of Tracy’s book. Just in case.

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Two Query Store Stories

Published 2020-03-10 by Kevin Feasel

Mark Wilkinson gives us two separate takes on Query Store:

When the Query Data Store (QDS) feature was announced for SQL Server 2016, we were excited about the prospect of being able to have deep insight on any query running in our environment. I work for a company that deals heavily in the e-commerce space, and we have a large SQL Server footprint. Our environment is unique in that is essentially a multi-tenant system, but all the tenants could have wildly different workloads. It’s really the kind of query execution scenario QDS was built for. We had the pleasure of working with the Microsoft SQLCAT team to get 2016 and QDS up and running in our production environment before it was GA.

In this post I’m going to share two stories about our QDS experience (from pre and post GA of the feature). One from the perspective of the Database Developer, and one from the Database Administrator. For the most part this is not a technical post full of queries and code samples. It’s just me talking about some things I have experienced using QDS in production.

CentralQDS, by the way, is really cool. Hopefully we’re able to show that to the world someday (and note how I say “we” even though I did absolutely nothing with it except for being in the same company as the people who developed it).

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Azure Data Studio and Query Store

Published 2020-03-10 by Kevin Feasel

Rob Farley explains why Azure Data Studio can’t be a 100% thing right now:

But the big thing with this new laptop is that I’ve made a conscious decision about what to install on it. And particularly, what things to NOT install.

For example, I’ve only installed SQL inside docker, not directly on Windows. I’m running the Linux version just because I can.

But today I feel like I’ve compromised.

Today I’ve installed SSMS, instead of persisting with just Azure Data Studio. It only took a week for me to cave, and the reason is Query Store.

Read on to understand why. I ended up having to cave on Docker-only for SQL Server because of PolyBase components that I needed and which aren’t (yet?) supported in the Linux version.

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Plan Forcing and Stored Procedure Alteration

Published 2020-03-06 by Kevin Feasel

Grant Fritchey takes us through a scenario where plan forcing with Query Store has some unexpected results:

I absolutely love Query Store and the ability it provides to force a plan is amazing. However, there are a lot of little gotchas in this functionality. I just recently found one that has quite a far reaching effect. Let’s talk about what happens when you DROP and then CREATE a stored procedure.

It’s one of those things where you read Grant’s blog post and say, “Yeah, of course that makes sense; how could it be otherwise?” And yet, without having read the blog post, the thought might never have occurred.

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Removing Ad Hoc Plans from the Query Store

Published 2020-02-20 by Kevin Feasel

Jeff Iannucci has a script which removes ad hoc plans from the Query Store:

Now, rather than being my usual rambling self I want to be very direct here: this solution will NOT give you the same behavior as “optimize for ad hoc workloads.” That setting keeps query info without the plan during the first execution, but then keeps the plan after the second execution.

That’s kinda like a surgeon with a scalpel. What is below is much more drastic. We’re going to break out a chainsaw for Query Store.

Chainsaw solutions to scalpel problems? Now you have my interest.

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Tracking Query Store Changes

Published 2020-02-05 by Kevin Feasel

Erin Stellato shows how to watch for Query Store changes whether due to settings modifications or running out of space:

The Query Store feature is a bit unique in that its status can change without user interference, which means it is important to understand how changes to Query Store are logged.  A couple weeks ago John Deardurff posted a question on Twitter asking specifically whether the SQL Server ERRORLOG is written to when the OPERATION_MODE changes to READ_ONLY because  MAX_STORAGE_SIZE_MB is exceeded.  I had never tested to confirm, but I know there is an event in Extended Events that will fire when the limit is reached.  I also know that when a user makes a change to a Query Store setting, it is logged in the ERRORLOG.

Click through to see how to watch for this and what the changes look like.

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Database Compatibility Level and Query Store

Published 2020-01-20 by Kevin Feasel

Erin Stellato gives us a moment of zen:

A question I’ve gotten a few times when teaching relates to database compatibility level and Query Store. I was talking to a client yesterday about post-upgrade plans and implementing Query Store, and the topic came again. They wanted to know what compatibility level the database needed in order to use Query Store.

The quick answer: it doesn’t matter.

Read on for a demonstration.

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