SQL Server 2012 supports parallel query execution. Before a query is executed, SQL Server’s cost-based optimizer estimates the cost of execution for a serial plan (that is, a plan that uses a single thread). The option to set the cost threshold for parallelism allows you to specify a threshold in seconds; if the cost of the serial execution plan (in seconds) is greater than the value specified by this parameter, SQL Server considers a parallel query execution plan. A query does not become a candidate for parallel query execution simply based on this fact. Because parallel query execution is supported only on multiprocessor servers, the
cost threshold for parallelism value is ignored ...