What Happens When Multiple Queries Compile at Once?

An interesting question came in on PollGab. DBAmusing asked: If a query takes 5-7s to calculate the execution plan (then executes <500ms) if multiple SPIDS all submit that query (different param values) when there’s no plan at start, does each SPID calc the execution plan, one after the other after waiting for the prior SPID to finish?

Join Limitations

Join Hints

SQL Server Clustered Index Seek Operation Generates Poor Query Performance

In this article, we look at why a SQL Server clustered index seek operation might not always be the most optimized approach for executing a query.

High Execution Plan Performance Variance

SQL Window Functions Series: LAG() and LEAD()

Dive deep into the powerful SQL window functions, LAG() and LEAD(). Explore their intricacies, discover real-world examples, and avoid common pitfalls.

Plansplaining, part 20. SQL Graph (part 1)

Welcome to part twenty of the plansplaining series. It has been a long time since I last wrote a plansplaining post, partly because of my health, but also for a large part because I was out of ideas. But recently I decided to dig a bit deeper into a feature that was released in SQL Server 2017 and that I had so far not played with: SQL Graph.

Don’t use DISTINCT as a “join-fixer”

I’ve quietly resolved performance issues by re-writing slow queries to avoid DISTINCT. Often, the DISTINCT is there only to serve as a “join-fixer,” and I can explain what that means using an example.

Improve Query Performance when SQL Server Ignores Nonclustered Index

In this article, we look at why SQL Server may not use a non-clustered index over the clustered index and what you can do to improve performance.

Explore Natively Compiled SQL Server Stored Procedure Execution Plans

In this article, we look at execution plans and performance of a natively compiled stored procedure versus a traditional stored procedure.