Hi, We have a Win 2008 R2 32 CPU SQL Server 2008 machine we use for SP2010. I'm trying to find a straight answer to a couple of questions about queries and MDOP. (1) Max degree of parallelism - as I understand it : 0 = use all CPUs on server with no exceptions 1 = suppress parallel plan generation 2 or greater = this is the number of CPUs to use for a single query's execution OK - so under what conditions would you change this setting? (2) We run Sp2010 - MS recommends in many docs that you set MDOP to 1 - but why? Surely with something hitting the db as hard as SP2010 you would want parallel plans being executed because you'd want as many CPUs being utilized at same time for similtaneous execution of code - or have I missed the general concept here? (3) Cost - could someone *please* define what "cost" is - it seems a dimensionless number, but if an execution plans segments are broken into bits, and each bit has a % cost, the overall of the plan can never exceed 1 ( 100% ). Additionally if we look at the "Cost Threshold for Parallelism" of say 5 ( as is the default ) - then if cost can never exceed 1, why is it set to 5? And how does the cost threshold relate to the max degree of parallelism, or maybe it doesnt? Any help trying to understand this is much appreciated........ Cheers SG.