diff --git a/CMakeLists.txt b/CMakeLists.txt
index 844ead632..0a31a5cff 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,6 +24,7 @@ option(HAVE_ICU       "BUild with ICU library" OFF)
 option(HAVE_TCMALLOC  "Build with tcmalloc library" ON)
 option(HAVE_LZ4       "Build with lz4 library" ON)
 option(HAVE_OPENMP    "Build with OpenMP" ON)
+option(HAVE_ANKERL    "Build with ankerl::unordered_dense::* library" OFF)
 option(BUILD_TESTS    "Build test suite" OFF)
 option(HAVE_WORD_ALIGNMENT "Build some structures as packed with 4-byte alignment" OFF)
 option(USE_UNITY_BUILD "Enable Unity Build" OFF)
diff --git a/cmake/config.h.in b/cmake/config.h.in
index b90d8b5d6..7390be97d 100644
--- a/cmake/config.h.in
+++ b/cmake/config.h.in
@@ -8,6 +8,7 @@
 #cmakedefine HAVE_ICU 1
 #cmakedefine HAVE_OVERPASS_XML 1
 #cmakedefine HAVE_WORD_ALIGNMENT 1
+#cmakedefine HAVE_ANKERL 0
 #cmakedefine OSMIUM_WITH_LZ4 1
 #cmakedefine HAVE_LIBOSMIUM ${HAVE_LIBOSMIUM}
 #cmakedefine PACKAGE_VERSION "${PACKAGE_VERSION}"
diff --git a/src/overpass_api/core/datatypes.h b/src/overpass_api/core/datatypes.h
index dc480b769..6b187bf79 100644
--- a/src/overpass_api/core/datatypes.h
+++ b/src/overpass_api/core/datatypes.h
@@ -1289,19 +1289,19 @@ struct Tags_By_Id_Cache
 {
 public:
   template <typename T>
-  std::unordered_map< typename T::Id_Type, kv_pairs> & get() = delete;
+  osm3s::unordered_map< typename T::Id_Type, kv_pairs> & get() = delete;
 
 private:
-  std::unordered_map< Node_Skeleton::Id_Type, kv_pairs > t_by_id_node;
-  std::unordered_map< Way_Skeleton::Id_Type, kv_pairs > t_by_id_way;
-  std::unordered_map< Relation_Skeleton::Id_Type, kv_pairs > t_by_id_relation;
-  std::unordered_map< Area_Skeleton::Id_Type, kv_pairs > t_by_id_area;
+  osm3s::unordered_map< Node_Skeleton::Id_Type, kv_pairs > t_by_id_node;
+  osm3s::unordered_map< Way_Skeleton::Id_Type, kv_pairs > t_by_id_way;
+  osm3s::unordered_map< Relation_Skeleton::Id_Type, kv_pairs > t_by_id_relation;
+  osm3s::unordered_map< Area_Skeleton::Id_Type, kv_pairs > t_by_id_area;
 };
 
-template<> inline std::unordered_map< Node_Skeleton::Id_Type, kv_pairs > &     Tags_By_Id_Cache::get< Node_Skeleton >()     { return t_by_id_node; }
-template<> inline std::unordered_map< Way_Skeleton::Id_Type, kv_pairs > &      Tags_By_Id_Cache::get< Way_Skeleton >()      { return t_by_id_way; }
-template<> inline std::unordered_map< Relation_Skeleton::Id_Type, kv_pairs > & Tags_By_Id_Cache::get< Relation_Skeleton >() { return t_by_id_relation; }
-template<> inline std::unordered_map< Area_Skeleton::Id_Type, kv_pairs > &     Tags_By_Id_Cache::get< Area_Skeleton >()     { return t_by_id_area; }
+template<> inline osm3s::unordered_map< Node_Skeleton::Id_Type, kv_pairs > &     Tags_By_Id_Cache::get< Node_Skeleton >()     { return t_by_id_node; }
+template<> inline osm3s::unordered_map< Way_Skeleton::Id_Type, kv_pairs > &      Tags_By_Id_Cache::get< Way_Skeleton >()      { return t_by_id_way; }
+template<> inline osm3s::unordered_map< Relation_Skeleton::Id_Type, kv_pairs > & Tags_By_Id_Cache::get< Relation_Skeleton >() { return t_by_id_relation; }
+template<> inline osm3s::unordered_map< Area_Skeleton::Id_Type, kv_pairs > &     Tags_By_Id_Cache::get< Area_Skeleton >()     { return t_by_id_area; }
 
 using user_id_name_t = std::vector< std::pair< uint32, std::string > >;
 
diff --git a/src/overpass_api/data/collect_items.h b/src/overpass_api/data/collect_items.h
index 84b28894e..7f1908891 100644
--- a/src/overpass_api/data/collect_items.h
+++ b/src/overpass_api/data/collect_items.h
@@ -748,9 +748,14 @@ std::vector< Index > get_indexes_
   Random_File< typename Skeleton::Id_Type, Index > current(rman.get_transaction()->random_index
       (current_skeleton_file_properties< Skeleton >()));
   for (auto it = ids.begin(); it != ids.end(); ++it)
-    result.push_back(current.get(it->val()));
+  {
+    auto v = current.get(it->val());
+    if (result.empty() || !(result.back() == v))
+      result.push_back(v);
+  }
 
-  std::sort(result.begin(), result.end());
+  if (!std::is_sorted(result.begin(), result.end()))
+    std::sort(result.begin(), result.end());
   result.erase(std::unique(result.begin(), result.end()), result.end());
 
   if (rman.get_desired_timestamp() != NOW || get_attic_idxs)
@@ -774,7 +779,8 @@ std::vector< Index > get_indexes_
     for (const auto & it : idx_list_db.as_discrete(idx_list_ids))
       result.push_back(it.object());
 
-    std::sort(result.begin(), result.end());
+    if (!std::is_sorted(result.begin(), result.end()))
+      std::sort(result.begin(), result.end());
     result.erase(std::unique(result.begin(), result.end()), result.end());
   }
 
diff --git a/src/overpass_api/data/collect_members.h b/src/overpass_api/data/collect_members.h
index 0b37b594f..68dc1df60 100644
--- a/src/overpass_api/data/collect_members.h
+++ b/src/overpass_api/data/collect_members.h
@@ -365,7 +365,7 @@ void filter_attic_elements
     // Confirm elements that are backed by meta data
     // Update element's expiration timestamp if a meta exists that is older than the current
     // expiration date and younger than timestamp
-    std::unordered_map< Index, std::unordered_map< typename Skeleton::Id_Type, std::pair< timestamp_t, timestamp_t > > >
+    osm3s::unordered_map< Index, osm3s::unordered_map< typename Skeleton::Id_Type, std::pair< timestamp_t, timestamp_t > > >
         timestamp_by_id_by_idx;
     for (typename std::map< Index, std::vector< Skeleton > >::const_iterator it = current.begin();
          it != current.end(); ++it)
@@ -390,7 +390,7 @@ void filter_attic_elements
           (attic_meta_file_properties< Skeleton >()));
 
     {
-      std::unordered_map< typename Skeleton::Id_Type, std::pair< timestamp_t, timestamp_t > > * entry = nullptr;
+      osm3s::unordered_map< typename Skeleton::Id_Type, std::pair< timestamp_t, timestamp_t > > * entry = nullptr;
 
       for (auto it = attic_meta_db.discrete_begin(idx_set.begin(), idx_set.end()); it != attic_meta_db.discrete_end(); ++it)
       {
@@ -418,7 +418,7 @@ void filter_attic_elements
           (current_meta_file_properties< Skeleton >()));
 
     {
-      std::unordered_map< typename Skeleton::Id_Type, std::pair< timestamp_t, timestamp_t > > * entry = nullptr;
+      osm3s::unordered_map< typename Skeleton::Id_Type, std::pair< timestamp_t, timestamp_t > > * entry = nullptr;
 
       for (auto it = meta_db.discrete_begin(idx_set.begin(), idx_set.end()); it != meta_db.discrete_end(); ++it)
       {
diff --git a/src/overpass_api/data/filter_ids_by_tags.h b/src/overpass_api/data/filter_ids_by_tags.h
index 2629342a0..8133a76b6 100644
--- a/src/overpass_api/data/filter_ids_by_tags.h
+++ b/src/overpass_api/data/filter_ids_by_tags.h
@@ -241,7 +241,7 @@ struct Tag_Entry_Listener_Value_Regex : public Tag_Entry_Listener< Id_Type >
   std::string value_;
   std::vector< Regular_Expression* > conditions_;
   const std::vector< Id_Type >* old_ids_;
-  std::map< Id_Type, std::pair< timestamp_t, timestamp_t > > timestamps;
+  osm3s::unordered_map< Id_Type, std::pair< timestamp_t, timestamp_t > > timestamps;
 };
 
 
@@ -295,8 +295,7 @@ struct Tag_Entry_Listener_Key_Regex : public Tag_Entry_Listener< Id_Type >
 
   void commit_ids()
   {
-    for (typename std::map< Id_Type, std::pair< timestamp_t, timestamp_t > >::const_iterator it = timestamps.begin();
-	it != timestamps.end(); ++it)
+    for (auto it = timestamps.begin(); it != timestamps.end(); ++it)
     {
       if (0 < it->second.first && it->second.first <= it->second.second)
         new_ids_.push_back(it->first);
@@ -310,7 +309,7 @@ struct Tag_Entry_Listener_Key_Regex : public Tag_Entry_Listener< Id_Type >
   Regular_Expression* value_;
   const std::vector< Id_Type >* old_ids_;
   std::vector< Id_Type > new_ids_;
-  std::map< Id_Type, std::pair< timestamp_t, timestamp_t > > timestamps;
+  osm3s::unordered_map< Id_Type, std::pair< timestamp_t, timestamp_t > > timestamps;
 };
 
 
diff --git a/src/overpass_api/data/set_comparison.cc b/src/overpass_api/data/set_comparison.cc
index 8bc25db34..03eb95dc1 100644
--- a/src/overpass_api/data/set_comparison.cc
+++ b/src/overpass_api/data/set_comparison.cc
@@ -368,12 +368,12 @@ std::vector< typename Skeleton::Id_Type > find_still_existing_skeletons
 
 
 template< typename Index, typename Skeleton >
-std::map< typename Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< typename Skeleton::Id_Type > >
+osm3s::unordered_map< typename Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< typename Skeleton::Id_Type > >
     find_meta_elements
     (Resource_Manager& rman, timestamp_t timestamp, const std::vector< Index >& idx_set,
      const std::vector< typename Skeleton::Id_Type >& searched_ids)
 {
-  std::map< typename Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< typename Skeleton::Id_Type > > result;
+  osm3s::unordered_map< typename Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< typename Skeleton::Id_Type > > result;
 
   Block_Backend< Index, OSM_Element_Metadata_Skeleton< typename Skeleton::Id_Type >,
         typename std::vector< Index >::const_iterator >
@@ -475,14 +475,14 @@ void Set_Comparison::clear_nodes(Resource_Manager& rman, bool add_deletion_infor
     std::vector< Node_Skeleton::Id_Type > found_ids
         = find_still_existing_skeletons< Uint32_Index, Node_Skeleton >(
             rman, rman.get_desired_timestamp(), req, searched_ids);
-    std::map< Node_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Node::Id_Type > > found_meta
+    osm3s::unordered_map< Node_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Node::Id_Type > > found_meta
         = find_meta_elements< Uint32_Index, Node_Skeleton >(rman, rman.get_diff_to_timestamp(), req, searched_ids);
 
     for (std::vector< Node_With_Context >::const_iterator it = nodes.begin(); it != nodes.end(); ++it)
     {
       if (it->idx.val() != 0xffu)
       {
-	std::map< Node_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Node::Id_Type > >::const_iterator
+        osm3s::unordered_map< Node_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Node::Id_Type > >::const_iterator
 	    meta_it = found_meta.find(it->elem.id);
 	result.different_nodes.push_back(std::make_pair(*it,
 	    Node_With_Context(monobound_binary_search(found_ids, it->elem.id) ? 0xfdu : 0xffu,
@@ -511,10 +511,10 @@ void Set_Comparison::clear_nodes(Resource_Manager& rman, bool add_deletion_infor
     {
       if (it->first.idx.val() == 0xffu)
       {
-        it->first.idx = std::binary_search(found_ids.begin(), found_ids.end(), it->second.elem.id) ? 0xfdu : 0xffu;
+        it->first.idx = monobound_binary_search(found_ids, it->second.elem.id) ? 0xfdu : 0xffu;
         it->first.elem = Node_Skeleton(it->second.elem.id);
 
-	std::map< Node_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Node::Id_Type > >::const_iterator
+        osm3s::unordered_map< Node_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Node::Id_Type > >::const_iterator
 	    meta_it = found_meta.find(it->second.elem.id);
         if (meta_it != found_meta.end())
           it->first.meta = meta_it->second;
@@ -604,14 +604,14 @@ void Set_Comparison::clear_ways(Resource_Manager& rman, bool add_deletion_inform
     std::vector< Way_Skeleton::Id_Type > found_ids
         = find_still_existing_skeletons< Uint31_Index, Way_Skeleton >(
             rman, rman.get_desired_timestamp(), req, searched_ids);
-    std::map< Way_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Way::Id_Type > > found_meta
+    osm3s::unordered_map< Way_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Way::Id_Type > > found_meta
         = find_meta_elements< Uint31_Index, Way_Skeleton >(rman, rman.get_diff_to_timestamp(), req, searched_ids);
 
     for (std::vector< Way_With_Context >::const_iterator it = ways.begin(); it != ways.end(); ++it)
     {
       if (it->idx.val() != 0xffu)
       {
-	std::map< Way_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Way::Id_Type > >::const_iterator
+        osm3s::unordered_map< Way_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Way::Id_Type > >::const_iterator
 	    meta_it = found_meta.find(it->elem.id);
 	result.different_ways.push_back(std::make_pair(*it,
 	    Way_With_Context(monobound_binary_search(found_ids, it->elem.id) ? 0xfdu : 0xffu,
@@ -644,7 +644,7 @@ void Set_Comparison::clear_ways(Resource_Manager& rman, bool add_deletion_inform
         it->first.idx = monobound_binary_search(found_ids, it->second.elem.id) ? 0xfdu : 0xffu;
         it->first.elem = Way_Skeleton(it->second.elem.id);
 
-	std::map< Way_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Way::Id_Type > >::const_iterator
+        osm3s::unordered_map< Way_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Way::Id_Type > >::const_iterator
 	    meta_it = found_meta.find(it->second.elem.id);
         if (meta_it != found_meta.end())
           it->first.meta = meta_it->second;
@@ -735,7 +735,8 @@ void Set_Comparison::clear_relations(Resource_Manager& rman, bool add_deletion_i
     std::vector< Relation_Skeleton::Id_Type > found_ids
         = find_still_existing_skeletons< Uint31_Index, Relation_Skeleton >(
             rman, rman.get_diff_to_timestamp(), req, searched_ids);
-    std::map< Relation_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Relation::Id_Type > > found_meta
+
+    osm3s::unordered_map< Relation_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Relation::Id_Type > > found_meta
         = find_meta_elements< Uint31_Index, Relation_Skeleton >(
             rman, rman.get_diff_to_timestamp(), req, searched_ids);
 
@@ -743,7 +744,7 @@ void Set_Comparison::clear_relations(Resource_Manager& rman, bool add_deletion_i
     {
       if (it->idx.val() != 0xffu)
       {
-	std::map< Relation_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Relation::Id_Type > >::const_iterator
+        osm3s::unordered_map< Relation_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Relation::Id_Type > >::const_iterator
 	    meta_it = found_meta.find(it->elem.id);
 	result.different_relations.push_back(std::make_pair(*it,
 	    Relation_With_Context(monobound_binary_search(found_ids, it->elem.id) ? 0xfdu : 0xffu,
@@ -776,7 +777,7 @@ void Set_Comparison::clear_relations(Resource_Manager& rman, bool add_deletion_i
         it->first.idx = monobound_binary_search(found_ids, it->second.elem.id) ? 0xfdu : 0xffu;
         it->first.elem = Relation_Skeleton(it->second.elem.id);
 
-	std::map< Relation_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Relation::Id_Type > >::const_iterator
+        osm3s::unordered_map< Relation_Skeleton::Id_Type, OSM_Element_Metadata_Skeleton< Relation::Id_Type > >::const_iterator
 	    meta_it = found_meta.find(it->second.elem.id);
         if (meta_it != found_meta.end())
           it->first.meta = meta_it->second;
diff --git a/src/overpass_api/data/tag_store.h b/src/overpass_api/data/tag_store.h
index d5dd81eff..70c036e73 100644
--- a/src/overpass_api/data/tag_store.h
+++ b/src/overpass_api/data/tag_store.h
@@ -56,7 +56,7 @@ class Tag_Store
   const std::vector< std::pair< std::string, std::string > >* get(const Index& index, const Object& elem);
 
 private:
-  std::unordered_map< typename Object::Id_Type, std::vector< std::pair< std::string, std::string > > > tags_by_id;
+  osm3s::unordered_map< typename Object::Id_Type, std::vector< std::pair< std::string, std::string > > > tags_by_id;
   Resource_Manager* rman = nullptr;
   Transaction* transaction = nullptr;
   bool use_index = false;
@@ -99,7 +99,7 @@ class Tag_Store< Uint31_Index, Derived_Structure >
 
 template< class Id_Type >
 void collect_attic_tags
-  (std::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
+  (osm3s::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
    const Block_Backend< Tag_Index_Local, Id_Type >& current_items_db,
    typename Block_Backend< Tag_Index_Local, Id_Type >::Range_Iterator& current_tag_it,
    const Block_Backend< Tag_Index_Local, Attic< Id_Type > >& attic_items_db,
@@ -206,7 +206,7 @@ void collect_attic_tags
 
 template< class Id_Type >
 void collect_attic_tags
-  (std::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
+  (osm3s::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
    const Block_Backend< Tag_Index_Local, Id_Type >& current_items_db,
    typename Block_Backend< Tag_Index_Local, Id_Type >::Range_Iterator& current_tag_it,
    const Block_Backend< Tag_Index_Local, Attic< Id_Type > >& attic_items_db,
@@ -263,7 +263,7 @@ void collect_tags
 
 template< class Id_Type >
 void collect_tags_single
-  (std::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
+  (osm3s::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
    const Block_Backend< Tag_Index_Local, Id_Type >& items_db,
    typename Block_Backend< Tag_Index_Local, Id_Type >::Range_Iterator& tag_it,
    const Id_Type id, uint32 coarse_index)
@@ -305,7 +305,7 @@ void collect_tags_single
 
 template< class Id_Type >
 void collect_tags
-  (std::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
+  (osm3s::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
    const Block_Backend< Tag_Index_Local, Id_Type >& items_db,
    typename Block_Backend< Tag_Index_Local, Id_Type >::Range_Iterator& tag_it,
    const std::vector< Id_Type >& ids, uint32 coarse_index)
@@ -350,7 +350,7 @@ void collect_tags
 
 template< class Id_Type >
 void collect_tags_framed
-  (std::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
+  (osm3s::unordered_map< Id_Type, std::vector< std::pair< std::string, std::string > > >& tags_by_id,
    const Block_Backend< Tag_Index_Local, Id_Type >& items_db,
    typename Block_Backend< Tag_Index_Local, Id_Type >::Range_Iterator& tag_it,
    std::map< uint32, std::vector< Id_Type > >& ids_by_coarse,
diff --git a/src/template_db/types.h b/src/template_db/types.h
index 74ceba01f..7516cc1b4 100644
--- a/src/template_db/types.h
+++ b/src/template_db/types.h
@@ -19,6 +19,11 @@
 #ifndef DE__OSM3S___TEMPLATE_DB__TYPES_H
 #define DE__OSM3S___TEMPLATE_DB__TYPES_H
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#undef VERSION
+#endif
+
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -34,14 +39,29 @@
 #include <sstream>
 #include <string>
 #include <type_traits>
+#include <unordered_map>
 #include <vector>
 
+#include "unordered_dense.h"
+
 #ifdef NATIVE_LARGE_FILES
 #define ftruncate64 ftruncate
 #define lseek64 lseek
 #define open64 open
 #endif
 
+namespace osm3s {
+  template< class Key, class T >
+#ifndef HAVE_ANKERL
+  using unordered_map = std::unordered_map< Key, T>;
+#else
+  using unordered_map = ankerl::unordered_dense::map< Key, T>;
+#endif
+
+  template< class Key, class T >
+  using map = std::map< Key, T>;
+}
+
 typedef unsigned int uint;
 
 typedef char int8;