Trimexcess on List(Of t) in .net

Question

After filling a list with the the needed strings, if the list won't be further appended, should trimexcess be called?

Answer 1

You certainly can, but keep in mind:

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 can be considerable, however, so the TrimExcess method does nothing if the list is at more than 90 percent of capacity.

I wouldn't worry too much about this unless you have found that large-allocated and sparsely-filled lists are taking up too much memory.

Answer 2

Calling TrimExcess after you load the list will likely save you some memory. But remember that if the items in your list are of a reference type (and strings are reference types), then all you're saving is the memory required to hold the references.

So, for example, if you have a List(of String) that's allocated for 2,000 items and there are only 1,000 items in it, calling TrimExcess is going to save you the memory occupied by 1,000 references. That's 4,000 bytes on the 32-bit runtime, and 8,000 bytes on the 64-bit runtime.

As Andrew Hare mentioned, calling TrimExcess after loading a list that's going to hang around in memory for a while is probably a good thing. You might also consider calling TrimExcess if you remove a whole bunch of things from a list, and then you're going to keep the list around. But calling TrimExcess repeatedly for the same list, unless it's really getting large, is just wasting time.