m_blocks.reserve(m_blocks.size() + 1);

//   clang++ -O3 -DNDEBUG -std=c++17 -I include bench_segmented_growth.cpp -o bench_segmented_growth
//   ./bench_segmented_growth

#include <ankerl/unordered_dense.h>

#include <chrono>
#include <cstdio>
#include <string>

int main() {
    static constexpr std::size_t targets[] = {250'000, 500'000, 1'000'000, 2'000'000, 4'000'000, 8'000'000};

    for (auto target : targets) {
        ankerl::unordered_dense::segmented_map<std::string, int> map;

        auto const t0 = std::chrono::steady_clock::now();
        for (std::size_t i = 0; i < target; ++i) {
            map.try_emplace(std::to_string(i), 0);
        }
        auto const t1 = std::chrono::steady_clock::now();

        std::printf("%.4f s  (%zu entries)\n", std::chrono::duration<double>(t1 - t0).count(), target);
    }
}

0.0498 s  (250000 entries)
0.1105 s  (500000 entries)
0.3333 s  (1000000 entries)
1.3306 s  (2000000 entries)
5.3910 s  (4000000 entries)
21.8044 s  (8000000 entries)

0.0468 s  (250000 entries)
0.0929 s  (500000 entries)
0.2095 s  (1000000 entries)
0.4428 s  (2000000 entries)
1.0223 s  (4000000 entries)
2.3013 s  (8000000 entries)

pointer block = std::allocator_traits<Allocator>::allocate(ba, num_elements_in_block);

if constexpr (ANKERL_UNORDERED_DENSE_HAS_EXCEPTIONS()) {
    try {
        m_blocks.push_back(block);
    } catch (...) {
        std::allocator_traits<Allocator>::deallocate(ba, block, num_elements_in_block);
        throw;
    }
} else {
    m_blocks.push_back(block);
}