All Eyes on the Wrong Problem: How Mitigations Distract from Real Performance Pain

The biggest lesson I’ve learned from helping folks manage data in Azure is this: if you’ve got a truly terrible problem you’d rather people didn’t notice, a great way to hide it is by educating your support staff and users about something bad but not AS terrible— something with a small mitigation—and constantly refocusing them on that.

The user base— and even your own support staff— will think that anyone who talks about the bigger issue just doesn’t understand how to fix the “known” problem.

This is the story of Azure General Purpose storage for Azure SQL Managed Instance and Azure SQL Database.

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What the Decline of SQL Server Quality Means for Developers and DBAs

‘Is it just me, or is SQL Server quality slipping?’

I asked myself that question for couple/few years until I faced up to it: SQL Server is well into a period where Microsoft investment is waning, and Microsoft regularly isn’t able to deliver the features they promise.

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Buyer Beware: Azure SQL Managed Instance Storage Is Regularly as Slow as 60 Seconds

What are your stories of unbelievably bad performance from cloud vendors? I’ll go first. For years, Azure SQL Managed Instance’s General Purpose Tier has documented ‘approximate’ storage latency as being “5-10 ms.” This week they added a footnote: “This is an average range. Although the vast majority of IO request durations will fall under the top of the range, outliers which exceed the range are possible.”

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How to Survive Opening a Microsoft Support Ticket for SQL Server or Azure SQL

Asking Microsoft for support for SQL Server or Azure SQL is a lousy experience these days, whether you’re using a cheaper service tier or the more expensive support tier formerly known as “Premiere Support.” You need to know a lot about the root cause of your problem and how to solve it, or your request will be dismissed with misinformation. You’ll need data and metrics to back up your claims to get the ticket escalated, and you’ll need to provide those receipts multiple times. Once escalated to the Product Group, you may get a helpful response, but it takes a while. If the answer is relayed through a lower support tier, it often won’t make much sense.

These issues aren’t due to bad work ethics or personal failings of support workers. These are good humans trying their best. The problem is worse because it’s systemic.

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General Failure Failed Forced Plans in Query Store Cause Even Slower Compile Times

This post demonstrates two related bugs with plan forcing in Query Store which increase the likelihood of slower query execution and application timeouts in SQL Server environments.

These bugs are most likely to impact you if:

• You use the Automatic Plan Correction feature in SQL Server, which automatically forces query plans.
• Anyone manually forces query plans with Query Store.
• You have slow storage, which can increase your likelihood of having longer compilation times.

The General Purpose tier of Azure SQL Managed Instance and Azure SQL Database feature both slow storage and Automatic Plan Correction enabled by default. So, weirdly enough, your risks of suffering from this problem are high if you are an Azure SQL customer.

Thanks to Erik Darling for his help in diagnosing and reproducing these issues– and his ‘slow compiler’ query used in this post was incredibly helpful to isolate and narrow down these problems.

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Slow Storage Can Cause Slow Compilation Time in SQL Server

Up till now, I’ve thought of compilation time in SQL Server as being dependent only on CPU resources– not something that requires fast storage to be speedy. But that’s not quite right.

Slow storage can result in periodic long compile time in SQL Server. And long compile time not only extends the runtime for the query, it can also result in blocking with waits for compile locks.

Thanks to Erik Darling for helping me figure this out, and explaining this all in his video, What Else Happens When Queries Try To Compile In SQL Server: COMPILE LOCKS!. For great details and demos, go watch that! I’ll be working through the topic with some simple flow charts here.

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Finally, a SQL Server Monitoring System That Leverages Query Store

I’ve spent a bit of time with Microsoft’s new database watcher tool for Azure SQL recently.

There are a lot of things I like about database watcher– which is currently in preview and which refuses to Capitalize Its Name– but it does one big thing that I really, really like: it collects data from Query Store. You can access that Query Store data from built-in database watcher dashboards, query it using KQL, or (something something) in Microsoft Fabric if you’ve got money to burn on your monitoring data.

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