How to reduce Garbage Collection performance Overhead

Question

MY application profiling showing a big Garbage Collection overhead. The profiler does'nt have a drill down into the Garbage Collection. What should I do to reduce this overhead?

I have many short-living arraylists and some long-lived that only die when the application shuts down.

Answer 1

Well basically you should reduce the work for the garbage collector. There a certain 'patterns' which produce a lot of work.

• Avoid having many objects with finalizers. Finalizers impose additional work on the garbage collector, because a object with a finalizer has to be collected twice.
• Avoid the 'midlife'-crisis. The .NET GC (on the desktop) is generational GC. When the object survive the first collection, but 'die' shortly after, the GC has done a lot of work for nothing. (coping to the second generation, collecting again, etc). So try to optimize the life-time of you objects in a way that they either die very quickly, or survive for a long, long time.
• Reduce unnecessary allocations. For example by using value type wisely. Or doing the work in a less memory-intensive way.

So in your case I guess that you either you've a 'midlife'-crisis with the short lived lists. Or you simple allocate list like mad.

In the first case: Try to make the life-span of the lists shorter. I can't tell you how the solution looks like for your application.

In the second case: Try to avoid allocation so many lists. Maybe you can use proper value-types? Or fixed sized arrays? Or change the structure of the code in such a way that less lists are needed?

Anyway, I would recommend to profile you applicaition and look how much you memory you allocate and how much can be collected in the first generation.

Answer 2

If you have too much garbage collection overhead, reduce your garbage. Try reusing lists ( preallocate and use them, clear them when done).

If you are using ArrayList with value types, try switching to use List<T> instead.