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 ...