Summary: A deep dive into SQL Server parallelism, and a potential performance problem with parallel plans that use TOP. There was an interesting question asked by Mark Storey-Smith on dba.stackexchange.com back in October 2011.  He was looking at the execution plan for a query that counts a million rows from a virtual auxiliary table of ...

Many people believe that whenever SQL Server creates an execution plan that uses parallelism, an alternative serial plan is also cached.  The idea seems to be that the execution engine then decides between the parallel and serial alternatives at runtime. I’ve seen this on forums, in blogs, and even in books.  In fairness, a lot of the ...

Last month a new PASS Virtual Chapter was introduced, one with a theme that is near and dear to much of what I like to work on: performance. Tomorrow, Tuesday August 3rd at noon Eastern time, the chapter will have its second meeting, and I will be doing the presentation. The topic is Parallelism and Performance. Here's the abstract:In ...

Welcome back for the second part of Parallelism Week here at SQL University. Get your pencils ready, and make sure to raise your hand if you have a question. Last time we covered the necessary background material to help you understand how the SQL Server Operating System schedules its many active threads, and the differences between its ...