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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The Restore-AzSqlInstanceDatabase Long Running Operation Failed Error on Azure SQL Managed Instance

What’s it like to be a Database Administrator for managed databases in Azure? Sometimes it’s a painful guessing game when a routine, core operation– restoring a database – fails with a most unhelpful error.

In this case, if the restore is run via PowerShell, following Microsoft guidance, the error message is:

Restore-AzSqlInstanceDatabase: Long running operation failed with status ‘Failed’. 
Additional Info: An unexpected error occured while processing the request.

The misspelling of “occurred” doesn’t bring confidence, but we try and try again.

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Erik Darling and Kendra Little Rate SQL Server Perf Tuning Techniques

Erik Darling joins Kendra Little to rate different SQL Server Performance Tuning Techniques in episode 81 of the Dear SQL DBA podcast. We share our opinions of… (deep breath)

Recompile hints, Query Store hints and plan forcing, CTEs, Resource Governor, the legacy cardinality estimator, Table Variables, Automatic Plan Correction, Batch Mode, index rebuilds, Hekaton, NOLOCK, page compression, partitioning, filtered indexes, columnstore, join hints, PSPO, indexed hints, indexed views, optimize for unknown, RCSI, adding more memory, restarting the damn thing, scalar UDFs, and Persisted Memory Grant Feedback.

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Learn Perf Tuning in 2 Days at PASS Summit 2024 With Erik Darling and Kendra Little

I’m teaming up with Erik Darling to teach you SQL Server Performance Tuning in two days at the PASS Data Community Summit in Seattle.

Erik and I are co-teaching both days of training to give you a strong strategic background on the internals you need to know, along with critical tactical performance tuning techniques. Join us to level up your perf tuning skills!

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Query Store Size Based Cleanup Causes Performance Problems - How to Avoid It

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.

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You Will Not Find Long Compilers Who Time Out in Query Store

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.

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How to Start an XEvents Trace on a Read Scale-Out Azure SQL Managed Instance

It took me more than half hour to figure out how to start an XEvents trace on a read-scale out instance of Azure SQL Managed Instance. It’s hard to monitor read scale-out instances, so tracing is desirable! I started with a simple trace of sql_statement_completed. Hopefully this saves other folks some time.

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