Dealing with plan regressions caused by changes to the query optimizer has been a royal pain for any development organization. Even if you manage to shield your customers with clever tricks from experiencing these in their end-user workloads, plan regressions are a major drain of resources during software development. Therefore, knowing whether a change in software (or configuration) is beneficial or detrimental is a huge benefit!
Together with my friends at Microsoft I’ve developed such an ‘early warning system’ for plan regressions based on relative orders within a plan space.
The details are in this paper, accepted at this year’s DBTest workshop at SIGMOD where we’ll talk about optimizer testing in detail — yet another good reason to book your ticket for Athens quick!