start_time = std::chrono::steady_clock::now();
for (auto entry : param_entries)
{
void* cell_buf = new char[entry.cell_size];
auto upsert_result = LocalStorage.emplace(entry.cell_id, CellEntry{ cell_buf, entry.cell_size, 0 });
if (!upsert_result.second)
{
std::swap(cell_buf, upsert_result.first->second.ptr);
delete[] cell_buf;
}
if (rand() % 3 == 0)
{
delete[] upsert_result.first->second.ptr;
LocalStorage.erase(entry.cell_id);
}
}
end_time = std::chrono::steady_clock::now();
He's not testing unordered_map performance alone, but the performance of new/delete & unordered_map. Also entry is a copy of param_entries's item, it should be changed to auto& entry. So he's essentially copying the whole array while iterating.
