Originally posted by chrisrlong

- Setting something to parallel is no silver bullet. A lot of variables are involved here as well. What are your configuration options? How many threads are attacking the problem? What is your I/O spread? How much did the plan change? Is this a statement that *should* be parallel? A good analogy I've heard is home repair: If you try to use 40 contractors to put in a bathroom sink, it's going to take longer than if you have just one. You don't actually want the 40 contractors until you're building an addition.
This is kind of what I was thinking as well. There's a certain amount of overhead when setting up a parallel query. In cases where your query runs for 5 seconds, that overhead is a significant portion. When your query takes 4 hours, that overhead is insignificant.