Execution Plan Stability
I’ve talked before about one of the primary things that the Query Optimizer team at Microsoft tries to avoid, regressions. Basically, they want a plan that worked well in SQL Server 2005 to work well in SQL Server 2008 R2. What’s more, they want everything to work well between service packs, updates and cumulative updates. Ever wonder how they do it? Well, they cheat. OK, that’s mean and not entirely accurate, but it gets the idea across. No, what they do is, identify when they have a breaking change, when they’ve got a special cumulative update or service pack that fixes some bad behavior, but that can cause plans to “break,†they wall it off. Note, in most cases, this “breakage†is actually a question of plans working correctly, but…