Code crimes, because even the Law needs to be broken
In 99.9% of the cases, if you see this, it is a mistake:
But I recently came into a place where this is actually a viable solution to a problem. The issue occurs deep inside RavenDB. And it boils down to a managed application not really having any way of actually assessing how much memory it is using.
What I would really like to be able to do is to specify a heap (using HeapCreate) and then say: “The following objects should be created on this heap”, which would allow to me to control exactly how much memory I am using for a particular task. In practice, that isn’t really possible (if you know how, please let me know).
What we do instead is to use as much memory as we can, based on the workload that we have. At certain point, we may hit an Out of Memory condition, which we take to mean, not that there is no more memory, but the system’s way of telling us to calm down.
By the time we reached the exception handler, we already lost all of the current workload, that means that now there is a LOT of garbage around for the GC. Before, when it tried to cleanup, we were actually holding to a lot of that memory, but not anymore.
Once an OOME happened, we can adjust our own behavior, to know that we are consuming too much memory and should be more conservative about our operations. We basically reset the clock back and become twice as conservative about using more memory. And if we get another OOME? We become twice as conservative again , and so on.
Eventually, even under high workloads and small amount of memory, we complete the task, and we can be sure that we make effective use of the system’s resources available to us.