Anyone working on SQL Server will have banged their head against a wall at one point or another trying to figure why a query hitting millions of rows isn’t being done in parallel. Well there have been a number of blogs posts about this, Craig Freedman’s excellent series on the query engine being the first http://blogs.msdn.com/b/craigfr/archive/2007/04/17/parallel-query-execution-presentation.aspx With the amazing Paul “query optimiser for a brain” White has a further list http://sqlblog.com/blogs...(read more)

http://sqlblogcasts.com/blogs/simons/archive/2015/04/26/non-parallelizable-operations-in-sql-server.aspx