diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3a3f6df..6f2e956 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,17 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 [Keep a CHANGELOG](http://keepachangelog.com).
 
 
+## Unreleased
+
+### Changed
+
+- several performance improvements
+
+
+[Compare v0.12.0...HEAD](https://github.com/rdf-elixir/rdf-ex/compare/v0.12.0...HEAD)
+
+
+
 ## 0.12.0 - 2022-04-11
 
 This version introduces a new graph builder DSL. See the [new guide](https://rdf-elixir.dev/rdf-ex/description-and-graph-dsl.html)
diff --git a/VERSION b/VERSION
index ac454c6..a5c379e 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.12.0
+0.12.1-pre
diff --git a/lib/rdf/data.ex b/lib/rdf/data.ex
index 811f330..c9f21ad 100644
--- a/lib/rdf/data.ex
+++ b/lib/rdf/data.ex
@@ -382,7 +382,8 @@ defimpl RDF.Data, for: RDF.Dataset do
   def objects(dataset), do: Dataset.objects(dataset)
   def resources(dataset), do: Dataset.resources(dataset)
 
-  def subject_count(dataset), do: dataset |> subjects |> Enum.count()
+  def subject_count(dataset), do: dataset |> subjects() |> MapSet.size()
+
   def statement_count(dataset), do: Dataset.statement_count(dataset)
   def values(dataset, opts \\ []), do: Dataset.values(dataset, opts)
   def map(dataset, fun), do: Dataset.map(dataset, fun)
diff --git a/lib/rdf/dataset.ex b/lib/rdf/dataset.ex
index db4ccf8..c820e71 100644
--- a/lib/rdf/dataset.ex
+++ b/lib/rdf/dataset.ex
@@ -528,7 +528,7 @@ defmodule RDF.Dataset do
   """
   @spec graph_count(t) :: non_neg_integer
   def graph_count(%__MODULE__{} = dataset) do
-    Enum.count(dataset.graphs)
+    map_size(dataset.graphs)
   end
 
   @doc """
diff --git a/lib/rdf/description.ex b/lib/rdf/description.ex
index bc5959e..a7fe708 100644
--- a/lib/rdf/description.ex
+++ b/lib/rdf/description.ex
@@ -488,7 +488,7 @@ defmodule RDF.Description do
     [{object, _}] = Enum.take(objects, 1)
 
     popped =
-      if Enum.count(objects) == 1,
+      if map_size(objects) == 1,
         do: elem(Map.pop(predications, predicate), 1),
         else: elem(pop_in(predications, [predicate, object]), 1)
 
@@ -633,7 +633,7 @@ defmodule RDF.Description do
   @spec statement_count(t) :: non_neg_integer
   def statement_count(%__MODULE__{} = description) do
     Enum.reduce(description.predications, 0, fn {_, objects}, count ->
-      count + Enum.count(objects)
+      count + map_size(objects)
     end)
   end
 
@@ -830,7 +830,7 @@ defmodule RDF.Description do
       | predications:
           Enum.reduce(description.predications, description.predications, fn
             {predicate, objects}, predications ->
-              original_object_count = Enum.count(predications)
+              original_object_count = map_size(predications)
 
               filtered_objects =
                 Enum.reject(objects, &match?({quoted_triple, _} when is_tuple(quoted_triple), &1))
diff --git a/lib/rdf/graph.ex b/lib/rdf/graph.ex
index a88792c..6922382 100644
--- a/lib/rdf/graph.ex
+++ b/lib/rdf/graph.ex
@@ -819,7 +819,7 @@ defmodule RDF.Graph do
   """
   @spec subject_count(t) :: non_neg_integer
   def subject_count(%__MODULE__{} = graph) do
-    Enum.count(graph.descriptions)
+    map_size(graph.descriptions)
   end
 
   @doc """