diff --git a/telegram-bot-api/Client.cpp b/telegram-bot-api/Client.cpp
index 515d42b..025fce3 100644
--- a/telegram-bot-api/Client.cpp
+++ b/telegram-bot-api/Client.cpp
@@ -3760,7 +3760,7 @@ void Client::check_chat_access(int64 chat_id, AccessRights access_rights, const
       CHECK(group_info != nullptr);
       if (!group_info->is_active && need_write_access) {
         if (group_info->upgraded_to_supergroup_id != 0) {
-          std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> parameters;
+          td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> parameters;
           auto updagraded_to_chat_id = get_supergroup_chat_id(group_info->upgraded_to_supergroup_id);
           parameters.emplace("migrate_to_chat_id", std::make_unique<td::VirtuallyJsonableLong>(updagraded_to_chat_id));
           return fail_query(400, "Bad Request: group chat was upgraded to a supergroup chat", std::move(query),
@@ -4398,7 +4398,8 @@ void Client::on_update(object_ptr<td_api::Object> result) {
     }
     case td_api::updateUser::ID: {
       auto update = move_object_as<td_api::updateUser>(result);
-      add_user(users_, std::move(update->user_));
+      auto *user_info = add_user_info(update->user_->id_);
+      add_user(user_info, std::move(update->user_));
       break;
     }
     case td_api::updateUserFullInfo::ID: {
@@ -4410,7 +4411,8 @@ void Client::on_update(object_ptr<td_api::Object> result) {
     }
     case td_api::updateBasicGroup::ID: {
       auto update = move_object_as<td_api::updateBasicGroup>(result);
-      add_group(groups_, std::move(update->basic_group_));
+      auto *group_info = add_group_info(update->basic_group_->id_);
+      add_group(group_info, std::move(update->basic_group_));
       break;
     }
     case td_api::updateBasicGroupFullInfo::ID: {
@@ -4425,7 +4427,8 @@ void Client::on_update(object_ptr<td_api::Object> result) {
     }
     case td_api::updateSupergroup::ID: {
       auto update = move_object_as<td_api::updateSupergroup>(result);
-      add_supergroup(supergroups_, std::move(update->supergroup_));
+      auto *supergroup_info = add_supergroup_info(update->supergroup_->id_);
+      add_supergroup(supergroup_info, std::move(update->supergroup_));
       break;
     }
     case td_api::updateSupergroupFullInfo::ID: {
@@ -6392,7 +6395,7 @@ void Client::on_message_send_succeeded(object_ptr<td_api::message> &&message, in
 
   auto query_id =
       extract_yet_unsent_message_query_id(chat_id, old_message_id, &message_info->is_reply_to_message_deleted);
-  auto &query = pending_send_message_queries_[query_id];
+  auto &query = *pending_send_message_queries_[query_id];
   if (query.is_multisend) {
     query.messages.push_back(td::json_encode<td::string>(JsonMessage(message_info, true, "sent message", this)));
     query.awaited_message_count--;
@@ -6420,7 +6423,7 @@ void Client::on_message_send_failed(int64 chat_id, int64 old_message_id, int64 n
   auto error = make_object<td_api::error>(result.code(), result.message().str());
 
   auto query_id = extract_yet_unsent_message_query_id(chat_id, old_message_id, nullptr);
-  auto &query = pending_send_message_queries_[query_id];
+  auto &query = *pending_send_message_queries_[query_id];
   if (query.is_multisend) {
     if (query.error == nullptr) {
       query.error = std::move(error);
@@ -8253,8 +8256,10 @@ void Client::do_send_message(object_ptr<td_api::InputMessageContent> input_messa
 td::int64 Client::get_send_message_query_id(PromisedQueryPtr query, bool is_multisend) {
   auto query_id = current_send_message_query_id_++;
   auto &pending_query = pending_send_message_queries_[query_id];
-  pending_query.query = std::move(query);
-  pending_query.is_multisend = is_multisend;
+  CHECK(pending_query == nullptr);
+  pending_query = td::make_unique<PendingSendMessageQuery>();
+  pending_query->query = std::move(query);
+  pending_query->is_multisend = is_multisend;
   return query_id;
 }
 
@@ -8276,7 +8281,7 @@ void Client::on_sent_message(object_ptr<td_api::message> &&message, int64 query_
   auto emplace_result = yet_unsent_messages_.emplace(yet_unsent_message_id, yet_unsent_message);
   CHECK(emplace_result.second);
   yet_unsent_message_count_[chat_id]++;
-  pending_send_message_queries_[query_id].awaited_message_count++;
+  pending_send_message_queries_[query_id]->awaited_message_count++;
 }
 
 void Client::abort_long_poll(bool from_set_webhook) {
@@ -8442,8 +8447,7 @@ void Client::long_poll_wakeup(bool force_flag) {
   }
 }
 
-void Client::add_user(std::unordered_map<int64, UserInfo> &users, object_ptr<td_api::user> &&user) {
-  auto user_info = &users[user->id_];
+void Client::add_user(UserInfo *user_info, object_ptr<td_api::user> &&user) {
   user_info->first_name = std::move(user->first_name_);
   user_info->last_name = std::move(user->last_name_);
   user_info->username = std::move(user->username_);
@@ -8475,23 +8479,31 @@ void Client::add_user(std::unordered_map<int64, UserInfo> &users, object_ptr<td_
   }
 }
 
+Client::UserInfo *Client::add_user_info(int64 user_id) {
+  auto emplace_result = users_.emplace(user_id, nullptr);
+  auto &user_info = emplace_result.first->second;
+  if (emplace_result.second) {
+    user_info = td::make_unique<UserInfo>();
+  } else {
+    CHECK(user_info != nullptr);
+  }
+  return user_info.get();
+}
+
 const Client::UserInfo *Client::get_user_info(int64 user_id) const {
   auto it = users_.find(user_id);
-  return it == users_.end() ? nullptr : &it->second;
+  return it == users_.end() ? nullptr : it->second.get();
 }
 
 void Client::set_user_bio(int64 user_id, td::string &&bio) {
-  auto user_info = &users_[user_id];
-  user_info->bio = std::move(bio);
+  add_user_info(user_id)->bio = std::move(bio);
 }
 
 void Client::set_user_has_private_forwards(int64 user_id, bool has_private_forwards) {
-  auto user_info = &users_[user_id];
-  user_info->has_private_forwards = has_private_forwards;
+  add_user_info(user_id)->has_private_forwards = has_private_forwards;
 }
 
-void Client::add_group(std::unordered_map<int64, GroupInfo> &groups, object_ptr<td_api::basicGroup> &&group) {
-  auto group_info = &groups[group->id_];
+void Client::add_group(GroupInfo *group_info, object_ptr<td_api::basicGroup> &&group) {
   group_info->member_count = group->member_count_;
   group_info->left = group->status_->get_id() == td_api::chatMemberStatusLeft::ID;
   group_info->kicked = group->status_->get_id() == td_api::chatMemberStatusBanned::ID;
@@ -8502,24 +8514,31 @@ void Client::add_group(std::unordered_map<int64, GroupInfo> &groups, object_ptr<
   }
 }
 
+Client::GroupInfo *Client::add_group_info(int64 group_id) {
+  auto emplace_result = groups_.emplace(group_id, nullptr);
+  auto &group_info = emplace_result.first->second;
+  if (emplace_result.second) {
+    group_info = td::make_unique<GroupInfo>();
+  } else {
+    CHECK(group_info != nullptr);
+  }
+  return group_info.get();
+}
+
 const Client::GroupInfo *Client::get_group_info(int64 group_id) const {
   auto it = groups_.find(group_id);
-  return it == groups_.end() ? nullptr : &it->second;
+  return it == groups_.end() ? nullptr : it->second.get();
 }
 
 void Client::set_group_description(int64 group_id, td::string &&descripton) {
-  auto group_info = &groups_[group_id];
-  group_info->description = std::move(descripton);
+  add_group_info(group_id)->description = std::move(descripton);
 }
 
 void Client::set_group_invite_link(int64 group_id, td::string &&invite_link) {
-  auto group_info = &groups_[group_id];
-  group_info->invite_link = std::move(invite_link);
+  add_group_info(group_id)->invite_link = std::move(invite_link);
 }
 
-void Client::add_supergroup(std::unordered_map<int64, SupergroupInfo> &supergroups,
-                            object_ptr<td_api::supergroup> &&supergroup) {
-  auto supergroup_info = &supergroups[supergroup->id_];
+void Client::add_supergroup(SupergroupInfo *supergroup_info, object_ptr<td_api::supergroup> &&supergroup) {
   supergroup_info->username = std::move(supergroup->username_);
   supergroup_info->date = supergroup->date_;
   supergroup_info->status = std::move(supergroup->status_);
@@ -8528,48 +8547,59 @@ void Client::add_supergroup(std::unordered_map<int64, SupergroupInfo> &supergrou
 }
 
 void Client::set_supergroup_description(int64 supergroup_id, td::string &&descripton) {
-  auto supergroup_info = &supergroups_[supergroup_id];
-  supergroup_info->description = std::move(descripton);
+  add_supergroup_info(supergroup_id)->description = std::move(descripton);
 }
 
 void Client::set_supergroup_invite_link(int64 supergroup_id, td::string &&invite_link) {
-  auto supergroup_info = &supergroups_[supergroup_id];
-  supergroup_info->invite_link = std::move(invite_link);
+  add_supergroup_info(supergroup_id)->invite_link = std::move(invite_link);
 }
 
 void Client::set_supergroup_sticker_set_id(int64 supergroup_id, int64 sticker_set_id) {
-  auto supergroup_info = &supergroups_[supergroup_id];
-  supergroup_info->sticker_set_id = sticker_set_id;
+  add_supergroup_info(supergroup_id)->sticker_set_id = sticker_set_id;
 }
 
 void Client::set_supergroup_can_set_sticker_set(int64 supergroup_id, bool can_set_sticker_set) {
-  auto supergroup_info = &supergroups_[supergroup_id];
-  supergroup_info->can_set_sticker_set = can_set_sticker_set;
+  add_supergroup_info(supergroup_id)->can_set_sticker_set = can_set_sticker_set;
 }
 
 void Client::set_supergroup_slow_mode_delay(int64 supergroup_id, int32 slow_mode_delay) {
-  auto supergroup_info = &supergroups_[supergroup_id];
-  supergroup_info->slow_mode_delay = slow_mode_delay;
+  add_supergroup_info(supergroup_id)->slow_mode_delay = slow_mode_delay;
 }
 
 void Client::set_supergroup_linked_chat_id(int64 supergroup_id, int64 linked_chat_id) {
-  auto supergroup_info = &supergroups_[supergroup_id];
-  supergroup_info->linked_chat_id = linked_chat_id;
+  add_supergroup_info(supergroup_id)->linked_chat_id = linked_chat_id;
 }
 
 void Client::set_supergroup_location(int64 supergroup_id, object_ptr<td_api::chatLocation> location) {
-  auto supergroup_info = &supergroups_[supergroup_id];
-  supergroup_info->location = std::move(location);
+  add_supergroup_info(supergroup_id)->location = std::move(location);
+}
+
+Client::SupergroupInfo *Client::add_supergroup_info(int64 supergroup_id) {
+  auto emplace_result = supergroups_.emplace(supergroup_id, nullptr);
+  auto &supergroup_info = emplace_result.first->second;
+  if (emplace_result.second) {
+    supergroup_info = td::make_unique<SupergroupInfo>();
+  } else {
+    CHECK(supergroup_info != nullptr);
+  }
+  return supergroup_info.get();
 }
 
 const Client::SupergroupInfo *Client::get_supergroup_info(int64 supergroup_id) const {
   auto it = supergroups_.find(supergroup_id);
-  return it == supergroups_.end() ? nullptr : &it->second;
+  return it == supergroups_.end() ? nullptr : it->second.get();
 }
 
 Client::ChatInfo *Client::add_chat(int64 chat_id) {
   LOG(DEBUG) << "Update chat " << chat_id;
-  return &chats_[chat_id];
+  auto emplace_result = chats_.emplace(chat_id, nullptr);
+  auto &chat_info = emplace_result.first->second;
+  if (emplace_result.second) {
+    chat_info = td::make_unique<ChatInfo>();
+  } else {
+    CHECK(chat_info != nullptr);
+  }
+  return chat_info.get();
 }
 
 const Client::ChatInfo *Client::get_chat(int64 chat_id) const {
@@ -8577,7 +8607,7 @@ const Client::ChatInfo *Client::get_chat(int64 chat_id) const {
   if (it == chats_.end()) {
     return nullptr;
   }
-  return &it->second;
+  return it->second.get();
 }
 
 Client::ChatType Client::get_chat_type(int64 chat_id) const {
@@ -8879,10 +8909,7 @@ void Client::add_new_message(object_ptr<td_api::message> &&message, bool is_edit
   }
 
   auto chat_id = message->chat_id_;
-  if (chat_id == 0) {
-    LOG(ERROR) << "Receive invalid chat in " << to_string(message);
-    return;
-  }
+  CHECK(chat_id != 0);
   new_message_queues_[chat_id].queue_.emplace(std::move(message), is_edited);
   process_new_message_queue(chat_id);
 }
@@ -8916,10 +8943,7 @@ void Client::add_new_chosen_inline_result(int64 sender_user_id, object_ptr<td_ap
 void Client::add_new_callback_query(object_ptr<td_api::updateNewCallbackQuery> &&query) {
   CHECK(query != nullptr);
   auto user_id = query->sender_user_id_;
-  if (user_id == 0) {
-    LOG(ERROR) << "Receive invalid sender in " << to_string(query);
-    return;
-  }
+  CHECK(user_id != 0);
   new_callback_query_queues_[user_id].queue_.push(std::move(query));
   process_new_callback_query_queue(user_id, 0);
 }
@@ -9806,6 +9830,6 @@ constexpr Client::Slice Client::API_ID_INVALID_ERROR_DESCRIPTION;
 constexpr int Client::CLOSING_ERROR_CODE;
 constexpr Client::Slice Client::CLOSING_ERROR_DESCRIPTION;
 
-std::unordered_map<td::string, td::Status (Client::*)(PromisedQueryPtr &query)> Client::methods_;
+td::FlatHashMap<td::string, td::Status (Client::*)(PromisedQueryPtr &query)> Client::methods_;
 
 }  // namespace telegram_bot_api
diff --git a/telegram-bot-api/Client.h b/telegram-bot-api/Client.h
index caefd33..0e8c116 100644
--- a/telegram-bot-api/Client.h
+++ b/telegram-bot-api/Client.h
@@ -19,6 +19,8 @@
 
 #include "td/utils/common.h"
 #include "td/utils/Container.h"
+#include "td/utils/FlatHashMap.h"
+#include "td/utils/FlatHashSet.h"
 #include "td/utils/JsonBuilder.h"
 #include "td/utils/Slice.h"
 #include "td/utils/Status.h"
@@ -27,8 +29,6 @@
 #include <limits>
 #include <memory>
 #include <queue>
-#include <unordered_map>
-#include <unordered_set>
 
 namespace telegram_bot_api {
 
@@ -588,9 +588,10 @@ class Client final : public WebhookActor::Callback {
     bool is_inline_bot = false;
     bool has_private_forwards = false;
   };
-  static void add_user(std::unordered_map<int64, UserInfo> &users, object_ptr<td_api::user> &&user);
+  static void add_user(UserInfo *user_info, object_ptr<td_api::user> &&user);
   void set_user_bio(int64 user_id, td::string &&bio);
   void set_user_has_private_forwards(int64 user_id, bool has_private_forwards);
+  UserInfo *add_user_info(int64 user_id);
   const UserInfo *get_user_info(int64 user_id) const;
 
   struct GroupInfo {
@@ -602,9 +603,10 @@ class Client final : public WebhookActor::Callback {
     bool is_active = false;
     int64 upgraded_to_supergroup_id = 0;
   };
-  static void add_group(std::unordered_map<int64, GroupInfo> &groups, object_ptr<td_api::basicGroup> &&group);
+  static void add_group(GroupInfo *group_info, object_ptr<td_api::basicGroup> &&group);
   void set_group_description(int64 group_id, td::string &&descripton);
   void set_group_invite_link(int64 group_id, td::string &&invite_link);
+  GroupInfo *add_group_info(int64 group_id);
   const GroupInfo *get_group_info(int64 group_id) const;
 
   struct SupergroupInfo {
@@ -621,8 +623,7 @@ class Client final : public WebhookActor::Callback {
     bool can_set_sticker_set = false;
     bool has_location = false;
   };
-  static void add_supergroup(std::unordered_map<int64, SupergroupInfo> &supergroups,
-                             object_ptr<td_api::supergroup> &&supergroup);
+  static void add_supergroup(SupergroupInfo *supergroup_info, object_ptr<td_api::supergroup> &&supergroup);
   void set_supergroup_description(int64 supergroup_id, td::string &&descripton);
   void set_supergroup_invite_link(int64 supergroup_id, td::string &&invite_link);
   void set_supergroup_sticker_set_id(int64 supergroup_id, int64 sticker_set_id);
@@ -630,6 +631,7 @@ class Client final : public WebhookActor::Callback {
   void set_supergroup_slow_mode_delay(int64 supergroup_id, int32 slow_mode_delay);
   void set_supergroup_linked_chat_id(int64 supergroup_id, int64 linked_chat_id);
   void set_supergroup_location(int64 supergroup_id, object_ptr<td_api::chatLocation> location);
+  SupergroupInfo *add_supergroup_info(int64 supergroup_id);
   const SupergroupInfo *get_supergroup_info(int64 supergroup_id) const;
 
   struct ChatInfo {
@@ -861,30 +863,30 @@ class Client final : public WebhookActor::Callback {
   int64 channel_bot_user_id_ = 0;
   int64 service_notifications_user_id_ = 0;
 
-  static std::unordered_map<td::string, Status (Client::*)(PromisedQueryPtr &query)> methods_;
+  static td::FlatHashMap<td::string, Status (Client::*)(PromisedQueryPtr &query)> methods_;
 
-  std::unordered_map<FullMessageId, std::unique_ptr<MessageInfo>, FullMessageIdHash> messages_;  // message cache
-  std::unordered_map<int64, UserInfo> users_;                                                    // user info cache
-  std::unordered_map<int64, GroupInfo> groups_;                                                  // group info cache
-  std::unordered_map<int64, SupergroupInfo> supergroups_;  // supergroup info cache
-  std::unordered_map<int64, ChatInfo> chats_;              // chat info cache
+  td::FlatHashMap<FullMessageId, std::unique_ptr<MessageInfo>, FullMessageIdHash> messages_;  // message cache
+  td::FlatHashMap<int64, td::unique_ptr<UserInfo>> users_;                                    // user info cache
+  td::FlatHashMap<int64, td::unique_ptr<GroupInfo>> groups_;                                  // group info cache
+  td::FlatHashMap<int64, td::unique_ptr<SupergroupInfo>> supergroups_;                        // supergroup info cache
+  td::FlatHashMap<int64, td::unique_ptr<ChatInfo>> chats_;                                    // chat info cache
 
-  std::unordered_map<FullMessageId, std::unordered_set<int64>, FullMessageIdHash>
+  td::FlatHashMap<FullMessageId, td::FlatHashSet<int64>, FullMessageIdHash>
       reply_message_ids_;  // message -> replies to it
-  std::unordered_map<FullMessageId, std::unordered_set<int64>, FullMessageIdHash>
+  td::FlatHashMap<FullMessageId, td::FlatHashSet<int64>, FullMessageIdHash>
       yet_unsent_reply_message_ids_;  // message -> replies to it
 
-  std::unordered_map<int32, td::vector<PromisedQueryPtr>> file_download_listeners_;
-  std::unordered_set<int32> download_started_file_ids_;
+  td::FlatHashMap<int32, td::vector<PromisedQueryPtr>> file_download_listeners_;
+  td::FlatHashSet<int32> download_started_file_ids_;
 
   struct YetUnsentMessage {
     int64 reply_to_message_id = 0;
     bool is_reply_to_message_deleted = false;
     int64 send_message_query_id = 0;
   };
-  std::unordered_map<FullMessageId, YetUnsentMessage, FullMessageIdHash> yet_unsent_messages_;
+  td::FlatHashMap<FullMessageId, YetUnsentMessage, FullMessageIdHash> yet_unsent_messages_;
 
-  std::unordered_map<int64, int32> yet_unsent_message_count_;
+  td::FlatHashMap<int64, int32> yet_unsent_message_count_;  // chat_id -> count
 
   struct PendingSendMessageQuery {
     PromisedQueryPtr query;
@@ -893,7 +895,7 @@ class Client final : public WebhookActor::Callback {
     td::vector<td::string> messages;
     object_ptr<td_api::error> error;
   };
-  std::unordered_map<int64, PendingSendMessageQuery>
+  td::FlatHashMap<int64, td::unique_ptr<PendingSendMessageQuery>>
       pending_send_message_queries_;  // query_id -> PendingSendMessageQuery
   int64 current_send_message_query_id_ = 1;
 
@@ -909,28 +911,28 @@ class Client final : public WebhookActor::Callback {
     std::queue<NewMessage> queue_;
     bool has_active_request_ = false;
   };
-  std::unordered_map<int64, NewMessageQueue> new_message_queues_;  // chat_id -> queue
+  td::FlatHashMap<int64, NewMessageQueue> new_message_queues_;  // chat_id -> queue
 
   struct NewCallbackQueryQueue {
     std::queue<object_ptr<td_api::updateNewCallbackQuery>> queue_;
     bool has_active_request_ = false;
   };
-  std::unordered_map<int64, NewCallbackQueryQueue> new_callback_query_queues_;  // sender_user_id -> queue
+  td::FlatHashMap<int64, NewCallbackQueryQueue> new_callback_query_queues_;  // sender_user_id -> queue
 
-  std::unordered_map<int64, td::string> sticker_set_names_;
+  td::FlatHashMap<int64, td::string> sticker_set_names_;
 
   int64 cur_temp_bot_user_id_ = 1;
-  std::unordered_map<td::string, int64> bot_user_ids_;
-  std::unordered_set<td::string> unresolved_bot_usernames_;
-  std::unordered_map<int64, int64> temp_to_real_bot_user_id_;
-  std::unordered_map<td::string, td::vector<int64>> awaiting_bot_resolve_queries_;
+  td::FlatHashMap<td::string, int64> bot_user_ids_;
+  td::FlatHashSet<td::string> unresolved_bot_usernames_;
+  td::FlatHashMap<int64, int64> temp_to_real_bot_user_id_;
+  td::FlatHashMap<td::string, td::vector<int64>> awaiting_bot_resolve_queries_;
 
   struct PendingBotResolveQuery {
     std::size_t pending_resolve_count = 0;
     PromisedQueryPtr query;
     td::Promise<PromisedQueryPtr> on_success;
   };
-  std::unordered_map<int64, PendingBotResolveQuery> pending_bot_resolve_queries_;
+  td::FlatHashMap<int64, PendingBotResolveQuery> pending_bot_resolve_queries_;
   int64 current_bot_resolve_query_id_ = 1;
 
   td::string dir_;
diff --git a/telegram-bot-api/ClientManager.cpp b/telegram-bot-api/ClientManager.cpp
index f0f023d..0630f21 100644
--- a/telegram-bot-api/ClientManager.cpp
+++ b/telegram-bot-api/ClientManager.cpp
@@ -71,9 +71,13 @@ void ClientManager::send(PromisedQueryPtr query) {
     return fail_query(401, "Unauthorized: invalid token specified", std::move(query));
   }
   auto r_user_id = td::to_integer_safe<td::int64>(query->token().substr(0, token.find(':')));
-  if (r_user_id.is_error() || r_user_id.ok() < 0 || !token_range_(r_user_id.ok())) {
+  if (r_user_id.is_error() || !token_range_(r_user_id.ok())) {
     return fail_query(421, "Misdirected Request: unallowed token specified", std::move(query));
   }
+  auto user_id = r_user_id.ok();
+  if (user_id <= 0 || user_id >= (static_cast<td::int64>(1) << 54)) {
+    return fail_query(401, "Unauthorized: invalid token specified", std::move(query));
+  }
 
   if (query->is_test_dc()) {
     token += "/test";
@@ -113,7 +117,7 @@ void ClientManager::send(PromisedQueryPtr query) {
       }
       flood_control.add_event(static_cast<td::int32>(now));
     }
-    auto tqueue_id = get_tqueue_id(r_user_id.ok(), query->is_test_dc());
+    auto tqueue_id = get_tqueue_id(user_id, query->is_test_dc());
     if (active_client_count_.find(tqueue_id) != active_client_count_.end()) {
       // return query->set_retry_after_error(1);
     }
@@ -392,6 +396,7 @@ void ClientManager::raw_event(const td::Event::Raw &event) {
   auto id = get_link_token();
   auto *info = clients_.get(id);
   CHECK(info != nullptr);
+  CHECK(info->tqueue_id_ != 0);
   auto &value = active_client_count_[info->tqueue_id_];
   if (event.ptr != nullptr) {
     value++;
diff --git a/telegram-bot-api/ClientManager.h b/telegram-bot-api/ClientManager.h
index 5720d98..1dcc093 100644
--- a/telegram-bot-api/ClientManager.h
+++ b/telegram-bot-api/ClientManager.h
@@ -16,11 +16,11 @@
 #include "td/utils/buffer.h"
 #include "td/utils/common.h"
 #include "td/utils/Container.h"
+#include "td/utils/FlatHashMap.h"
 #include "td/utils/FloodControlFast.h"
 #include "td/utils/Slice.h"
 
 #include <memory>
-#include <unordered_map>
 #include <utility>
 
 namespace telegram_bot_api {
@@ -61,9 +61,9 @@ class ClientManager final : public td::Actor {
   std::shared_ptr<const ClientParameters> parameters_;
   TokenRange token_range_;
 
-  std::unordered_map<td::string, td::uint64> token_to_id_;
-  std::unordered_map<td::string, td::FloodControlFast> flood_controls_;
-  std::unordered_map<td::int64, td::uint64> active_client_count_;
+  td::FlatHashMap<td::string, td::uint64> token_to_id_;
+  td::FlatHashMap<td::string, td::FloodControlFast> flood_controls_;
+  td::FlatHashMap<td::int64, td::uint64> active_client_count_;
 
   bool close_flag_ = false;
   td::vector<td::Promise<td::Unit>> close_promises_;
diff --git a/telegram-bot-api/Query.cpp b/telegram-bot-api/Query.cpp
index 41c66dd..d8fb3b9 100644
--- a/telegram-bot-api/Query.cpp
+++ b/telegram-bot-api/Query.cpp
@@ -21,7 +21,7 @@
 
 namespace telegram_bot_api {
 
-std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> empty_parameters;
+td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> empty_parameters;
 
 Query::Query(td::vector<td::BufferSlice> &&container, td::Slice token, bool is_test_dc, td::MutableSlice method,
              td::vector<std::pair<td::MutableSlice, td::MutableSlice>> &&args,
@@ -96,7 +96,7 @@ void Query::set_error(int http_status_code, td::BufferSlice result) {
 void Query::set_retry_after_error(int retry_after) {
   retry_after_ = retry_after;
 
-  std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> parameters;
+  td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> parameters;
   parameters.emplace("retry_after", std::make_unique<td::VirtuallyJsonableLong>(retry_after));
   set_error(429, td::json_encode<td::BufferSlice>(
                      JsonQueryError(429, PSLICE() << "Too Many Requests: retry after " << retry_after, parameters)));
diff --git a/telegram-bot-api/Query.h b/telegram-bot-api/Query.h
index f5d15f8..ed40911 100644
--- a/telegram-bot-api/Query.h
+++ b/telegram-bot-api/Query.h
@@ -15,6 +15,7 @@
 
 #include "td/utils/buffer.h"
 #include "td/utils/common.h"
+#include "td/utils/FlatHashMap.h"
 #include "td/utils/JsonBuilder.h"
 #include "td/utils/List.h"
 #include "td/utils/port/IPAddress.h"
@@ -23,7 +24,6 @@
 
 #include <algorithm>
 #include <memory>
-#include <unordered_map>
 #include <utility>
 
 namespace telegram_bot_api {
@@ -164,11 +164,11 @@ td::StringBuilder &operator<<(td::StringBuilder &sb, const Query &query);
 
 // fix for outdated C++14 libraries
 // https://stackoverflow.com/questions/26947704/implicit-conversion-failure-from-initializer-list
-extern std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> empty_parameters;
+extern td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> empty_parameters;
 
 class JsonParameters final : public td::Jsonable {
  public:
-  explicit JsonParameters(const std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters)
+  explicit JsonParameters(const td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters)
       : parameters_(parameters) {
   }
   void store(td::JsonValueScope *scope) const {
@@ -180,7 +180,7 @@ class JsonParameters final : public td::Jsonable {
   }
 
  private:
-  const std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters_;
+  const td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters_;
 };
 
 template <class T>
@@ -206,7 +206,7 @@ class JsonQueryError final : public td::Jsonable {
  public:
   JsonQueryError(
       int error_code, td::Slice description,
-      const std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters = empty_parameters)
+      const td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters = empty_parameters)
       : error_code_(error_code), description_(description), parameters_(parameters) {
   }
   void store(td::JsonValueScope *scope) const {
@@ -222,7 +222,7 @@ class JsonQueryError final : public td::Jsonable {
  private:
   int error_code_;
   td::Slice description_;
-  const std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters_;
+  const td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters_;
 };
 
 class PromiseDeleter {
@@ -261,7 +261,7 @@ void answer_query(const Jsonable &result, PromisedQueryPtr query, td::Slice desc
 
 inline void fail_query(
     int http_status_code, td::Slice description, PromisedQueryPtr query,
-    const std::unordered_map<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters = empty_parameters) {
+    const td::FlatHashMap<td::string, std::unique_ptr<td::VirtuallyJsonable>> &parameters = empty_parameters) {
   query->set_error(http_status_code,
                    td::json_encode<td::BufferSlice>(JsonQueryError(http_status_code, description, parameters)));
   query.reset();  // send query into promise explicitly
diff --git a/telegram-bot-api/WebhookActor.cpp b/telegram-bot-api/WebhookActor.cpp
index bfab715..14df122 100644
--- a/telegram-bot-api/WebhookActor.cpp
+++ b/telegram-bot-api/WebhookActor.cpp
@@ -379,11 +379,14 @@ void WebhookActor::load_updates() {
 
   for (auto &update : updates) {
     VLOG(webhook) << "Load update " << update.id;
-    if (update_map_.find(update.id) != update_map_.end()) {
-      LOG(ERROR) << "Receive duplicated event " << update.id << " from tqueue";
+    CHECK(update.id.is_valid());
+    auto &dest_ptr = update_map_[update.id];
+    if (dest_ptr != nullptr) {
+      LOG(ERROR) << "Receive duplicated event " << update.id << " from TQueue";
       continue;
     }
-    auto &dest = update_map_[update.id];
+    dest_ptr = td::make_unique<Update>();
+    auto &dest = *dest_ptr;
     dest.id_ = update.id;
     dest.json_ = update.data.str();
     dest.delay_ = 1;
@@ -437,7 +440,7 @@ void WebhookActor::load_updates() {
 void WebhookActor::drop_event(td::TQueue::EventId event_id) {
   auto it = update_map_.find(event_id);
   CHECK(it != update_map_.end());
-  auto queue_id = it->second.queue_id_;
+  auto queue_id = it->second->queue_id_;
   update_map_.erase(it);
 
   auto queue_updates_it = queue_updates_.find(queue_id);
@@ -448,8 +451,10 @@ void WebhookActor::drop_event(td::TQueue::EventId event_id) {
   if (queue_updates_it->second.event_ids.empty()) {
     queue_updates_.erase(queue_updates_it);
   } else {
-    auto &update = update_map_[queue_updates_it->second.event_ids.front()];
-    queues_.emplace(update.wakeup_at_, update.queue_id_);
+    auto update_id = queue_updates_it->second.event_ids.front();
+    CHECK(update_id.is_valid());
+    auto &update = update_map_[update_id];
+    queues_.emplace(update->wakeup_at_, update->queue_id_);
   }
 
   parameters_->shared_data_->tqueue_->forget(tqueue_id_, event_id);
@@ -462,7 +467,7 @@ void WebhookActor::on_update_ok(td::TQueue::EventId event_id) {
   auto it = update_map_.find(event_id);
   CHECK(it != update_map_.end());
 
-  VLOG(webhook) << "Receive ok for update " << event_id << " in " << (last_success_time_ - it->second.last_send_time_)
+  VLOG(webhook) << "Receive ok for update " << event_id << " in " << (last_success_time_ - it->second->last_send_time_)
                 << " seconds";
 
   drop_event(event_id);
@@ -474,21 +479,22 @@ void WebhookActor::on_update_error(td::TQueue::EventId event_id, td::Slice error
 
   auto it = update_map_.find(event_id);
   CHECK(it != update_map_.end());
+  CHECK(it->second != nullptr);
+  auto &update = *it->second;
 
   const int MAX_RETRY_AFTER = 3600;
   retry_after = td::clamp(retry_after, 0, MAX_RETRY_AFTER);
-  int next_delay = it->second.delay_;
+  int next_delay = update.delay_;
   int next_effective_delay = retry_after;
-  if (retry_after == 0 && it->second.fail_count_ > 0) {
+  if (retry_after == 0 && update.fail_count_ > 0) {
     next_delay = td::min(WEBHOOK_MAX_RESEND_TIMEOUT, next_delay * 2);
     next_effective_delay = next_delay;
   }
-  if (parameters_->shared_data_->get_unix_time(now) + next_effective_delay > it->second.expires_at_) {
+  if (parameters_->shared_data_->get_unix_time(now) + next_effective_delay > update.expires_at_) {
     LOG(WARNING) << "Drop update " << event_id << ": " << error;
     drop_event(event_id);
     return;
   }
-  auto &update = it->second;
   update.delay_ = next_delay;
   update.wakeup_at_ = now + next_effective_delay;
   update.fail_count_++;
@@ -514,10 +520,15 @@ td::Status WebhookActor::send_update() {
   }
 
   auto queue_id = it->id;
+  CHECK(queue_id != 0);
   queues_.erase(it);
   auto event_id = queue_updates_[queue_id].event_ids.front();
+  CHECK(event_id.is_valid());
 
-  auto &update = update_map_[event_id];
+  auto update_map_it = update_map_.find(event_id);
+  CHECK(update_map_it != update_map_.end());
+  CHECK(update_map_it->second != nullptr);
+  auto &update = *update_map_it->second;
   update.last_send_time_ = now;
 
   auto body = td::json_encode<td::BufferSlice>(JsonUpdate(update.id_.value(), update.json_));
diff --git a/telegram-bot-api/WebhookActor.h b/telegram-bot-api/WebhookActor.h
index 6067d73..71d702e 100644
--- a/telegram-bot-api/WebhookActor.h
+++ b/telegram-bot-api/WebhookActor.h
@@ -20,6 +20,7 @@
 #include "td/utils/BufferedFd.h"
 #include "td/utils/common.h"
 #include "td/utils/Container.h"
+#include "td/utils/FlatHashMap.h"
 #include "td/utils/FloodControlFast.h"
 #include "td/utils/HttpUrl.h"
 #include "td/utils/JsonBuilder.h"
@@ -35,7 +36,6 @@
 #include <memory>
 #include <set>
 #include <tuple>
-#include <unordered_map>
 
 namespace telegram_bot_api {
 
@@ -127,8 +127,8 @@ class WebhookActor final : public td::HttpOutboundConnection::Callback {
       return std::hash<td::int32>()(event_id.value());
     }
   };
-  std::unordered_map<td::TQueue::EventId, Update, EventIdHash> update_map_;
-  std::unordered_map<td::int64, QueueUpdates> queue_updates_;
+  td::FlatHashMap<td::TQueue::EventId, td::unique_ptr<Update>, EventIdHash> update_map_;
+  td::FlatHashMap<td::int64, QueueUpdates> queue_updates_;
   std::set<Queue> queues_;
   td::int64 unique_queue_id_ = static_cast<td::int64>(1) << 60;