Re: [hibernate-dev] Memory consumption

Hi Steve, On the list again, my bad... On Thu, May 17, 2012 at 1:07 PM, Steve Ebersole<steve(a)hibernate.org> wrote: > I am not following what you are saying about "reusing keys" and optimizers. > Nor how it might lead to bad execution plans. Can you elaborate on your > thoughts here? If you have a lot of (OR primaryKey=value) clauses with the same value, if the optimizer doesn't deduplicate the clauses, the statistics used by the planner to build the query plan might be wrong and lead to bad query plans. At least some of the optimizers out there don't remove identical values as it's a lot of cycles usually wasted for nothing as nobody writes query like that. Simplified example: if you have 100 (OR primaryKey=1) clauses, the planner might consider that you'll have 100 values returned which is plain wrong in this case. It's not important if the query is simple and you don't have a lot of joins but if you're in the case of a complex object hierarchy with a lot of left joins, it might lead to really bad execution plans.