count the number of collisions in densh_hash_map

[liuzqt]

I want to find out how 'bad' the collision happened in a dense_hash_map.

I found my dense_hash_map performance drop dramatically in some continuous key range (it's almost 10-15x slower) so I suppose there're bad collision happened in these key ranges. So I want to know how bad it's, as a hint to determine whether I need to rehash, or choose a better hash func.

in std::unordered_map I can do

std::unordered_map<int, int> m;
// insert some data into m
int max_collision = 0;
for (int i = 0; i < m.bucket_count(); ++i) {
  max_collision = std::max(int(m.bucket_size(i)), max_collision);
}

but dense_hash_map.bucket_size() only return 1 or 0, I guess it's closed addressing hash map implementation. So is there a way to count the number of collisions in densh_hash_map?