How to check performance difference between 2 identical SQL Servers?

Say you have two identical SQL Servers with similar databases in two different branches. Only the database sizes differ by about 20% and server machine are also identical. You will get a complaint that the performance of one is very very low compare to another, so how to find the issue to resolve?

If you have a test platform it is better to restore the database from the live server and ensure you have similar levels of hardware, application version and hot fixes.

The procedure is to isolate the query in question from your application. Apart from the SHOWPLAN, you must enable STATISTICS IO and STATISTICS TIME before running the query (refer to the Books Online for more information about setting these three set statements on). You must run UPDATE STATISTICS on all objects involved in the query. If the query is in the form of a stored procedure or view, it must be re-created and rerun.

Consequently, you need to run the query in question several times, as the required data in the cache may affect query performance. For a valid comparison, the queries must be the same, and must be running against the same data set.