Maps and memory leaks
When maps grow and shrink, buckets need to be added to the underlying data structure to support it.
Mistake
When shrinking a map, the elements will be garbage collected, however the buckets will still remain.
Fix
Either create a new map and copy all the elements of the old map to it. This would result in a brief window of high memory consumption considering the two maps, but the old map would be eventually collected. Alternatively, make the values pointers. Pointers take up less memory and even though the buckets will still remain, there should be significantly less of them.