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Category: Query Store

Query Store Size-Based Cleanup Performance Issues

Published 2024-04-24 by Kevin Feasel

Kendra Little has a public service announcement:

I’m a huge fan of SQL Server’s Query Store feature. Query Store collects query execution plans and aggregate query performance metrics, including wait stats. Having Query Store enabled makes troubleshooting performance issues such as bad parameter sniffing, much, much easier. Because Query Store is integrated into SQL Server itself, it also can catch query plans in a lightweight way that an external monitoring system will often miss.

When performance matters, it’s important to ensure that you’re managing Query Store so that Query Store cleanup does not run during high volume times. Query Store cleanup could slow your workload down significantly.

Read on for more information. I’d also like to plug qdstoolbox, an open-source solution some of my former colleagues worked on. This includes QDSCacheCleanup, which works considerably better than the built-in cleanup process.

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Working with Query Store Hints

Published 2024-04-04 by Kevin Feasel

Etienne Lopes shares some thoughts around a new feature in SQL Server 2022:

Last December I got lucky since after upgrading from SQL Server 2012 to 2022, one of my clients had a process running in a particular database that went from around 10 minutes to around 10 hours!

You might be thinking: “It got 60 times worse, where’s the luck in that?”

Well, it presented me with a great opportunity to try a new feature in SQL Server 2022 called “Query Store Hints” (in a real production environment) and confirm the fabulous results that can be obtained by using it, with no effort at all. I thought it could be worth to share this experience and that’s what I’ll present in this post 

Click through for more details on the problem and solution.

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Query Compilation Timeouts and Query Store

Published 2024-03-06 by Kevin Feasel

Kendra Little diagnoses a problem:

Last November, a puzzle was really bothering me. Some queries from an application were timing out frequently after running for 30 seconds, but they were halfway invisible in the SQL Server.

I say “halfway invisible” because I could see the queries while they were running in SQL Server’s dynamic management views using free tools (sp_WhoIsActive and sp_BlitzWho).

But the queries had some odd characteristics:

Through the power of communication with other humans (eew, that idea sounds icky), Kendra was able to learn what the problem was and how you can track such issues outside of Query Store.

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Recompile Hints and Query Store

Published 2024-02-09 by Kevin Feasel

Erik Darling talks about one very popular tool and one very popular technique and what happens when they mix:

But let’s say one day you have performance issues regardless of all the recompiling in the world. No matter what set of parameters get passed in, your procedure is just sleepy-dog slow.

Things get so bad that you hire a young, handsome consultant with reasonable rates like myself to help you figure out why.

The plan cache will be pretty useless for troubleshooting the recompile-hinted queries, but we can still use Query Store.

Read on for more detail and a demonstration.

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Automated Alerts for Query Store Usage in Azure SQL DB

Published 2023-11-03 by Kevin Feasel

Jose Manuel Jurado Diaz doesn’t want to run out of disk space:

In this article, we will introduce a PowerShell script that helps monitor the usage of Query Data Store (QDS) in SQL Server databases. The script automatically sends an email alert when the storage space used by the Query Data Store reaches or exceeds 80% of its maximum allocated space. This can be particularly useful for database administrators to proactively manage and optimize their database storage.

Before we dive into the details, it’s essential to note that the script provided is a recommendation and should be adapted according to your specific environment and requirements. The responsibility of ensuring its compatibility and the impact on your system lies solely with the user.

Click through for the script. A quick glance of the code makes me think it will also work with on-premises SQL Server.

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Finding a Particular Query Plan in Query Store’s UI

Published 2023-08-01 by Kevin Feasel

Andrea Allred does a search:

I have this problem where I want to see how a newly released query is performing, but it may not be bad enough to make any of the canned reports that SQL Server provides in QueryStore. I was able to look up the plan handle, but always struggled to get to the query id for QueryStore, until now.

Click through for a query to retrieve the query ID and then how to find data on that particular query. I’d also recommend QDSToolbox for more detailed query analysis.

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Monitoring Query Store State Changes

Published 2023-06-30 by Kevin Feasel

Jose Manuel Jurado Diaz wants to know when the Query Store state changes:

This morning, I have been working on a support case where our client was not able to see certain queries when querying the Query Data Store. We have observed that the cause is due to the Query Data Store changing to a read-only mode due to the volume of data and the limitation our client had on the QDS database space. Therefore, I would like to share the following PowerShell script that can be executed at regular intervals to check and retrieve when the state of QDS has changed. Unfortunately, in Azure SQL Database, we cannot use the Extended Event ‘qds.query_store_db_diagnostics’.

Click through to see Jose’s alternative solution.

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Query Hints: Ad Hoc vs Query Store

Published 2023-06-29 by Kevin Feasel

Grant Fritchey sets up a showdown:

I recently presented a session on the Query Store at Data Saturday Rhineland and the question came up: If there’s already a query hint on a query, what happens when you try to force a similar query hint?

Yeah, OK, that is a weird one. I don’t know the answer, but I’m about to find out.

Click through for a very interesting demo. To be honest, I expected the opposite result, so this was surprising.

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