Question

I have a List container which can potentially have up to 100,000 items in to start with. While the program is running this list will slowly empty, should I alter the capacity as I empty the list?

I have done some testing and execution time seems to be the same, but is there much overhead to lowering the capacity of a list? I can find lots of information about increasing the capacity but not much on lowering it.

Answer 1

Unless you have a very low amount of memory, this is a micro-optimization.

Normally, there is no need to change the capacity of a List<>.

From the TrimExcess method documentation:

This method can be used to minimize a collection’s memory overhead if no new elements will be added to the collection. The cost of reallocating and copying a large List<T> can be considerable, however, so the TrimExcess method does nothing if the list is at more than 90 percent of capacity. This avoids incurring a large reallocation cost for a relatively small gain.