diff --git a/include/ylt/metric/counter.hpp b/include/ylt/metric/counter.hpp
index 35170ebd8..43dc40b35 100644
--- a/include/ylt/metric/counter.hpp
+++ b/include/ylt/metric/counter.hpp
@@ -147,12 +147,12 @@ class basic_dynamic_counter
              std::move(labels_name)) {}
   using label_key_type = const std::array<std::string, N> &;
   void inc(label_key_type labels_value, value_type value = 1) {
-    detail::inc_impl(Base::try_emplace(labels_value)->value, value);
+    detail::inc_impl(Base::try_emplace(labels_value).first->value, value);
   }
 
   value_type update(label_key_type labels_value, value_type value) {
     return Base::try_emplace(labels_value)
-        ->value.exchange(value, std::memory_order::relaxed);
+        .first->value.exchange(value, std::memory_order::relaxed);
   }
 
   value_type value(label_key_type labels_value) {
diff --git a/include/ylt/metric/dynamic_metric.hpp b/include/ylt/metric/dynamic_metric.hpp
index f8198a4f2..9753fb93c 100644
--- a/include/ylt/metric/dynamic_metric.hpp
+++ b/include/ylt/metric/dynamic_metric.hpp
@@ -91,18 +91,16 @@ class dynamic_metric_impl : public dynamic_metric {
 
  protected:
   template <typename Key, typename... Args>
-  std::shared_ptr<metric_pair> try_emplace(Key&& key, Args&&... args) {
+  std::pair<std::shared_ptr<metric_pair>, bool> try_emplace(Key&& key,
+                                                            Args&&... args) {
     std::span<const std::string, N> view = key;
-    auto iter =
-        map_.try_emplace(view, std::forward<Key>(key),  // rehash problem
-                         std::forward<Args>(args)...);
-    if (iter.second) {
-      *const_cast<std::span<const std::string, N>*>(&iter.first.first) =
-          iter.first.second->label;
-    }
-    return map_
-        .try_emplace(view, std::forward<Key>(key), std::forward<Args>(args)...)
-        .first.second;
+    return map_.try_emplace_with_op(
+        view,
+        [](auto result) {
+          *const_cast<std::span<const std::string, N>*>(&result.first->first) =
+              result.first->second->label;
+        },
+        std::forward<Key>(key), std::forward<Args>(args)...);
   }
   void clean_expired_label() override {
     erase_if([now = std::chrono::steady_clock::now()](auto& pair) mutable {
diff --git a/include/ylt/metric/gauge.hpp b/include/ylt/metric/gauge.hpp
index 5701dcf0c..41b689a4a 100644
--- a/include/ylt/metric/gauge.hpp
+++ b/include/ylt/metric/gauge.hpp
@@ -54,7 +54,7 @@ class basic_dynamic_gauge : public basic_dynamic_counter<value_type, N> {
 
   void dec(const std::array<std::string, N>& labels_value,
            value_type value = 1) {
-    detail::dec_impl(Base::try_emplace(labels_value)->value, value);
+    detail::dec_impl(Base::try_emplace(labels_value).first->value, value);
   }
 };
 
diff --git a/include/ylt/metric/summary.hpp b/include/ylt/metric/summary.hpp
index 9e90c2d58..7d36c86ec 100644
--- a/include/ylt/metric/summary.hpp
+++ b/include/ylt/metric/summary.hpp
@@ -156,33 +156,34 @@ class basic_dynamic_summary
   }
 
   void observe(const std::array<std::string, N>& labels_value, float value) {
-    Base::try_emplace(labels_value, quantiles_)->value.insert(value);
+    Base::try_emplace(labels_value, quantiles_).first->value.insert(value);
   }
 
   std::vector<float> get_rates(const std::array<std::string, N>& labels_value) {
     double sum;
     uint64_t count;
     return Base::try_emplace(labels_value, quantiles_)
-        ->value.get_rates(sum, count);
+        .first->value.get_rates(sum, count);
   }
 
   std::vector<float> get_rates(const std::array<std::string, N>& labels_value,
                                uint64_t& count) {
     double sum;
     return Base::try_emplace(labels_value, quantiles_)
-        ->value.get_rates(sum, count);
+        .first->value.get_rates(sum, count);
   }
 
   std::vector<float> get_rates(const std::array<std::string, N>& labels_value,
                                double& sum) {
     uint64_t count;
     return Base::try_emplace(labels_value, quantiles_)
-        ->value.get_rates(sum, count);
+        .first->value.get_rates(sum, count);
   }
 
   std::vector<float> get_rates(const std::array<std::string, N>& labels_value,
                                double& sum, uint64_t& count) {
-    return Base::try_emplace(labels_value, quantiles_)->value.stat(sum, count);
+    return Base::try_emplace(labels_value, quantiles_)
+        .first->value.stat(sum, count);
   }
 
   virtual void serialize(std::string& str) override {
diff --git a/include/ylt/util/map_sharded.hpp b/include/ylt/util/map_sharded.hpp
index 2add54559..c1c255a3b 100644
--- a/include/ylt/util/map_sharded.hpp
+++ b/include/ylt/util/map_sharded.hpp
@@ -28,20 +28,13 @@ class map_lock_t {
     return it->second;
   }
 
-  template <typename... Args>
-  std::pair<value_type&, bool> try_emplace(const key_type& key,
-                                           Args&&... args) {
+  template <typename Op, typename... Args>
+  std::pair<std::shared_ptr<typename mapped_type::element_type>, bool>
+  try_emplace_with_op(const key_type& key, Op&& op, Args&&... args) {
     std::lock_guard lock(*mtx_);
     auto result = visit_map().try_emplace(key, std::forward<Args>(args)...);
-    return {*result.first, result.second};
-  }
-
-  template <typename... Args>
-  std::pair<value_type&, bool> try_emplace(key_type&& key, Args&&... args) {
-    std::lock_guard lock(*mtx_);
-    auto result =
-        visit_map().try_emplace(std::move(key), std::forward<Args>(args)...);
-    return {*result.first, result.second};
+    op(result);
+    return {result.first->second, result.second};
   }
 
   size_t erase(const key_type& key) {
@@ -118,39 +111,49 @@ template <typename Map, typename Hash>
 class map_sharded_t {
  public:
   using key_type = typename Map::key_type;
-  using value_type = typename Map::mapped_type;
+  using value_type = typename Map::value_type;
+  using mapped_type = typename Map::mapped_type;
   map_sharded_t(size_t shard_num) : shards_(shard_num) {}
 
-  template <typename... Args>
-  auto try_emplace(key_type&& key, Args&&... args) {
-    auto result = get_sharded(Hash{}(key))
-                      .try_emplace(std::move(key), std::forward<Args>(args)...);
-    if (result.second) {
-      size_.fetch_add(1, std::memory_order_relaxed);
+  template <typename KeyType, typename... Args>
+  std::pair<std::shared_ptr<typename mapped_type::element_type>, bool>
+  try_emplace(KeyType&& key, Args&&... args) {
+    return try_emplace_with_op(
+        std::forward<KeyType>(key),
+        [](auto&&) {
+        },
+        std::forward<Args>(args)...);
+  }
+
+  template <typename Op, typename... Args>
+  std::pair<std::shared_ptr<typename mapped_type::element_type>, bool>
+  try_emplace_with_op(const key_type& key, Op&& func, Args&&... args) {
+    auto ret = get_sharded(Hash{}(key))
+                   .try_emplace_with_op(key, std::forward<Op>(func),
+                                        std::forward<Args>(args)...);
+    if (ret.second) {
+      size_.fetch_add(1);
     }
-    return result;
+    return ret;
   }
 
-  template <typename... Args>
-  auto try_emplace(const key_type& key, Args&&... args) {
-    auto result =
-        get_sharded(Hash{}(key)).try_emplace(key, std::forward<Args>(args)...);
-    if (result.second) {
-      size_.fetch_add(1, std::memory_order_relaxed);
+  size_t size() const {  // this value is approx
+    int64_t val = size_.load();
+    if (val < 0) [[unlikely]] {  // may happen when insert & deleted frequently
+      val = 0;
     }
-    return result;
+    return val;
   }
 
-  size_t size() const { return size_.load(std::memory_order_relaxed); }
-
-  auto find(const key_type& key) const {
+  std::shared_ptr<typename mapped_type::element_type> find(
+      const key_type& key) const {
     return get_sharded(Hash{}(key)).find(key);
   }
 
   size_t erase(const key_type& key) {
     auto result = get_sharded(Hash{}(key)).erase(key);
     if (result) {
-      size_.fetch_sub(result, std::memory_order_relaxed);
+      size_.fetch_sub(result);
     }
     return result;
   }
@@ -161,7 +164,7 @@ class map_sharded_t {
     for (auto& map : shards_) {
       auto result = map.erase_if(std::forward<Func>(op));
       total += result;
-      size_.fetch_sub(result, std::memory_order_relaxed);
+      size_.fetch_sub(result);
     }
     return total;
   }
@@ -173,7 +176,7 @@ class map_sharded_t {
       auto result = map.erase_if(std::forward<Func>(op));
       if (result) {
         total += result;
-        size_.fetch_sub(result, std::memory_order_relaxed);
+        size_.fetch_sub(result);
         break;
       }
     }
@@ -191,7 +194,7 @@ class map_sharded_t {
   template <typename T>
   std::vector<T> copy(auto&& op) const {
     std::vector<T> ret;
-    ret.reserve(size_.load(std::memory_order_relaxed));
+    ret.reserve(size());
     for (auto& map : shards_) {
       map.for_each([&ret, &op](auto& e) {
         if (op(e.second)) {
@@ -217,6 +220,6 @@ class map_sharded_t {
   }
 
   std::vector<internal::map_lock_t<Map>> shards_;
-  std::atomic<std::size_t> size_;
+  std::atomic<int64_t> size_;
 };
 }  // namespace ylt::util
\ No newline at end of file
diff --git a/src/metric/benchmark/bench.hpp b/src/metric/benchmark/bench.hpp
index ce9e42777..b464df58d 100644
--- a/src/metric/benchmark/bench.hpp
+++ b/src/metric/benchmark/bench.hpp
@@ -1,3 +1,4 @@
+#include <exception>
 #include <random>
 
 #include "ylt/metric.hpp"
@@ -38,7 +39,7 @@ void bench_mixed_impl(IMPL& impl, WRITE_OP&& op, size_t thd_num,
     vec.push_back(std::thread([&, i] {
       bench_clock_t clock_loop;
       auto dur = clock.duration<std::chrono::microseconds>();
-      while (!stop || dur < duration * 2) {
+      while (!stop && dur < duration + 1s) {
         op();
         auto new_dur = clock.duration<std::chrono::microseconds>();
         lantency_summary.observe((new_dur - dur).count() / 1000.0f);
@@ -105,7 +106,8 @@ inline void bench_static_counter_mixed(size_t thd_num,
 
 inline void bench_dynamic_summary_mixed(size_t thd_num,
                                         std::chrono::seconds duration,
-                                        std::chrono::seconds age = 1s) {
+                                        std::chrono::seconds age = 1s,
+                                        int max_cnt = 1000000) {
   ylt::metric::dynamic_summary summary("dynamic summary mixed test", "",
                                        {0.5, 0.9, 0.95, 0.99, 0.995},
                                        {"a", "b"}, age);
@@ -113,14 +115,34 @@ inline void bench_dynamic_summary_mixed(size_t thd_num,
       summary,
       [&]() mutable {
         summary.observe({"123e4567-e89b-12d3-a456-426614174000",
-                         std::to_string(get_random(1000000))},
+                         std::to_string(get_random(max_cnt))},
                         get_random(100));
       },
       thd_num, duration);
 }
 
+inline void bench_dynamic_counter_mixed_with_delete(
+    size_t thd_num, std::chrono::seconds duration,
+    std::chrono::seconds age = 1s, int max_cnt = 1000000) {
+  ylt::metric::dynamic_counter_2d counter("dynamic summary mixed test", "",
+                                          {"a", "b"});
+  bench_mixed_impl(
+      counter,
+      [&, i = 0]() mutable {
+        ++i;
+        std::array<std::string, 2> label = {
+            "123e4567-e89b-12d3-a456-426614174000",
+            std::to_string(get_random(max_cnt))};
+        counter.inc(label, 1);
+        counter.remove_label_value({{"a", label[0]}, {"b", label[1]}});
+      },
+      thd_num, duration);
+}
+
 inline void bench_dynamic_counter_mixed(size_t thd_num,
-                                        std::chrono::seconds duration) {
+                                        std::chrono::seconds duration,
+                                        std::chrono::seconds age = 1s,
+                                        int max_cnt = 1000000) {
   ylt::metric::dynamic_counter_2d counter("dynamic summary mixed test", "",
                                           {"a", "b"});
   bench_mixed_impl(
@@ -128,7 +150,7 @@ inline void bench_dynamic_counter_mixed(size_t thd_num,
       [&, i = 0]() mutable {
         ++i;
         counter.inc({"123e4567-e89b-12d3-a456-426614174000",
-                     std::to_string(get_random(1000000))},
+                     std::to_string(get_random(max_cnt))},
                     1);
       },
       thd_num, duration);
diff --git a/src/metric/tests/parallel_test.cpp b/src/metric/tests/parallel_test.cpp
index 8f0f2e3b1..80b35ea04 100644
--- a/src/metric/tests/parallel_test.cpp
+++ b/src/metric/tests/parallel_test.cpp
@@ -8,6 +8,9 @@
 TEST_CASE("test high parallel perform test") {
   bench_static_summary_mixed(std::thread::hardware_concurrency() * 4, 3s);
   bench_dynamic_summary_mixed(std::thread::hardware_concurrency() * 4, 3s);
+  // TODO: add bench_dynamic_summary_mixed_with_delete
   bench_static_counter_mixed(std::thread::hardware_concurrency() * 4, 3s);
   bench_dynamic_counter_mixed(std::thread::hardware_concurrency() * 4, 3s);
+  bench_dynamic_counter_mixed_with_delete(
+      std::thread::hardware_concurrency() * 4, 3s, 1s, 2);
 }
\ No newline at end of file