Compare showplan and output from dbcc 310 and 302 which you gathered in Chapter 2, “Analyze: Documenting Business Requirements”, to that of the test system to verify that the optimizer is making the same decisions. Some possible causes of optimizer differences include:
Data and data distribution problems. Check data layout and be sure that these match the productions system.
Index definitions. Verify that your reindexing scripts worked. Using sp_helpindex, compare the index definitions of the production and test systems.
Resolve any problems before going on.