diff --git a/lib/phoenix/pubsub/pg2.ex b/lib/phoenix/pubsub/pg2.ex
index 83907490..801fefd6 100644
--- a/lib/phoenix/pubsub/pg2.ex
+++ b/lib/phoenix/pubsub/pg2.ex
@@ -62,20 +62,16 @@ defmodule Phoenix.PubSub.PG2 do
     name = Keyword.fetch!(opts, :name)
     pool_size = Keyword.get(opts, :pool_size, 1)
     adapter_name = Keyword.fetch!(opts, :adapter_name)
-    Supervisor.start_link(__MODULE__, {name, adapter_name, pool_size}, name: :"#{adapter_name}_supervisor")
+    Supervisor.start_link(__MODULE__, {name, adapter_name, pool_size}, name: adapter_name)
   end
 
   @impl true
   def init({name, adapter_name, pool_size}) do
-    [_ | groups] =
+    groups =
       for number <- 1..pool_size do
         :"#{adapter_name}_#{number}"
       end
 
-    # Use `adapter_name` for the first in the pool for backwards compatability
-    # with v2.0 when the pool_size is 1.
-    groups = [adapter_name | groups]
-
     :persistent_term.put(adapter_name, List.to_tuple(groups))
 
     children =
diff --git a/lib/phoenix/tracker.ex b/lib/phoenix/tracker.ex
index 269da817..d276115b 100644
--- a/lib/phoenix/tracker.ex
+++ b/lib/phoenix/tracker.ex
@@ -210,6 +210,13 @@ defmodule Phoenix.Tracker do
     |> Phoenix.Tracker.Shard.list(topic)
   end
 
+  @spec dirty_list(atom, topic) :: [presence]
+  def dirty_list(tracker_name, topic) do
+    tracker_name
+    |> Shard.name_for_topic(topic, pool_size(tracker_name))
+    |> Phoenix.Tracker.Shard.dirty_list(topic)
+  end
+
   @doc """
   Gets presences tracked under a given topic and key pair.
 
@@ -231,6 +238,35 @@ defmodule Phoenix.Tracker do
     |> Phoenix.Tracker.Shard.get_by_key(topic, key)
   end
 
+  @spec dirty_get_by_key(atom, topic, term) :: [presence]
+  def dirty_get_by_key(tracker_name, topic, key) do
+    tracker_name
+    |> Shard.name_for_topic(topic, pool_size(tracker_name))
+    |> Phoenix.Tracker.Shard.dirty_get_by_key(topic, key)
+  end
+
+  @spec dirty_get_by_key(atom, term) :: [{topic, pid, meta :: map()}]
+  def dirty_get_by_key(tracker_name, key) do
+    0..(pool_size(tracker_name) - 1)
+    |> Enum.flat_map(fn n ->
+      shard_name = Shard.name_for_number(tracker_name, n)
+
+      Phoenix.Tracker.Shard.dirty_get_by_key(shard_name, key)
+    end)
+  end
+
+  @spec dirty_get_by_key_with_limit(atom, term, integer()) :: [{topic, pid, meta :: map()}]
+  def dirty_get_by_key_with_limit(tracker_name, key, limit) do
+    upper_bound_limit_per_shard = ceil(limit / pool_size(tracker_name))
+    0..(pool_size(tracker_name) - 1)
+    |> Enum.flat_map(fn n ->
+      shard_name = Shard.name_for_number(tracker_name, n)
+
+      Phoenix.Tracker.Shard.dirty_get_by_key_with_limit(shard_name, key, upper_bound_limit_per_shard)
+    end)
+    |> Enum.take(limit)
+  end
+
   @doc """
   Gracefully shuts down by broadcasting permdown to all replicas.
 
@@ -245,6 +281,17 @@ defmodule Phoenix.Tracker do
     Supervisor.stop(tracker_name)
   end
 
+  @doc false
+  @spec size(atom) :: non_neg_integer
+  def size(tracker_name) do
+    0..(pool_size(tracker_name) - 1)
+    |> Enum.reduce(0, fn n, acc ->
+      shard_name = Shard.name_for_number(tracker_name, n)
+
+      Phoenix.Tracker.Shard.size(shard_name) + acc
+    end)
+  end
+
   @doc """
   Starts a tracker pool.
 
diff --git a/lib/phoenix/tracker/shard.ex b/lib/phoenix/tracker/shard.ex
index 6fd792b6..4c77b9d4 100644
--- a/lib/phoenix/tracker/shard.ex
+++ b/lib/phoenix/tracker/shard.ex
@@ -86,11 +86,31 @@ defmodule Phoenix.Tracker.Shard do
     |> State.get_by_key(topic, key)
   end
 
+  @spec dirty_get_by_key(atom, topic, term) :: [presence]
+  def dirty_get_by_key(shard_name, topic, key) do
+    State.tracked_key(shard_name, topic, key, [])
+  end
+
+  @spec dirty_get_by_key(atom, term) :: [presence]
+  def dirty_get_by_key(shard_name, key) do
+    State.tracked_key(shard_name, key, [])
+  end
+
+  @spec dirty_get_by_key_with_limit(atom, term, integer()) :: [presence]
+  def dirty_get_by_key_with_limit(shard_name, key, limit) do
+    State.tracked_key_with_limit(shard_name, key, [], limit)
+  end
+
   @spec graceful_permdown(pid) :: :ok
   def graceful_permdown(server_pid) do
     GenServer.call(server_pid, :graceful_permdown)
   end
 
+  @spec size(atom) :: non_neg_integer
+  def size(shard_name) do
+    State.size(shard_name)
+  end
+
   ## Server
 
   def start_link(tracker, tracker_opts, pool_opts) do
diff --git a/lib/phoenix/tracker/state.ex b/lib/phoenix/tracker/state.ex
index 1d5949cc..75526f86 100644
--- a/lib/phoenix/tracker/state.ex
+++ b/lib/phoenix/tracker/state.ex
@@ -57,11 +57,16 @@ defmodule Phoenix.Tracker.State do
       replica: replica,
       context: %{replica => 0},
       mode: :normal,
-      values: :ets.new(shard_name, [:named_table, :protected, :ordered_set]),
+      values: :ets.new(shard_name, [:named_table, :protected, :ordered_set, write_concurrency: :true]),
       pids: :ets.new(:pids, [:duplicate_bag]),
       replicas: %{replica => :up}})
   end
 
+  @spec size(atom) :: non_neg_integer
+  def size(table) do
+    :ets.info(table, :size)
+  end
+
   @doc """
   Returns the causal context for the set.
   """
@@ -161,6 +166,37 @@ defmodule Phoenix.Tracker.State do
         [{{:"$1", :"$2"}}]}])
   end
 
+  def tracked_key(table, key, down_replicas) do
+    :ets.select(
+      table,
+      [
+        {
+          {{:"$1", :"$2", key}, :"$3", {:"$4", :_}},
+          not_in(:"$4", down_replicas),
+          [{{:"$1", :"$2", :"$3"}}]
+        }
+      ]
+    )
+  end
+
+  def tracked_key_with_limit(table, key, down_replicas, limit) do
+    :ets.select(
+      table,
+      [
+        {
+          {{:"$1", :"$2", key}, :"$3", {:"$4", :_}},
+          not_in(:"$4", down_replicas),
+          [{{:"$1", :"$2", :"$3"}}]
+        }
+      ],
+      limit
+    )
+    |> case do
+      {lst, _} -> lst
+      _ -> []
+    end
+  end
+
   defp not_in(_pos, []), do: []
   defp not_in(pos, replicas), do: [not: ors(pos, replicas)]
   defp ors(pos, [rep]), do: {:"=:=", pos, {rep}}
diff --git a/test/phoenix/tracker/pool_test.exs b/test/phoenix/tracker/pool_test.exs
index e7bd1071..74715ae2 100644
--- a/test/phoenix/tracker/pool_test.exs
+++ b/test/phoenix/tracker/pool_test.exs
@@ -35,9 +35,51 @@ defmodule Phoenix.Tracker.PoolTest do
     end
 
     @tag pool_size: pool_size
-    test "pool #{pool_size}: Untrack/4 results in all ids being untracked",
-      %{server: server} do
+    test "pool #{pool_size}: dirty_get_by_key/2 returns presences from all shards", %{server: server} do
+      topics = for i <- 1..100, do: "topic_#{i}"
+
+      refs =
+        for topic <- topics do
+          {:ok, ref} = Tracker.track(server, self(), topic, "me", %{name: "me"})
+          ref
+        end
+
+      for topic <- topics do
+        {:ok, _} = Tracker.track(server, self(), topic, "other", %{name: "me"})
+      end
+
+      by_key = Tracker.dirty_get_by_key(server, "me")
+      assert length(by_key) == 100
+
+      topics_and_refs =
+        for {topic, pid, %{name: "me", phx_ref: ref}} <- by_key do
+          assert pid == self()
+          {topic, ref}
+        end
+
+      assert Enum.sort(topics_and_refs) == Enum.sort(List.zip([topics, refs]))
+    end
+
+    @tag pool_size: pool_size
+    test "pool #{pool_size}: dirty_get_by_key_with_limit/2 returns at most limit num results", %{server: server} do
+      limit = Enum.random([1, 2, 5, 1000])
+      topics = for i <- 1..2000, do: "topic_#{i}"
+
+      for topic <- topics do
+        {:ok, _} = Tracker.track(server, self(), topic, "me", %{name: "me"})
+      end
+
+      for topic <- topics do
+        {:ok, _} = Tracker.track(server, self(), topic, "other", %{name: "me"})
+      end
 
+      res = Tracker.dirty_get_by_key_with_limit(server, "me", limit)
+      assert length(res) <= limit
+    end
+
+    @tag pool_size: pool_size
+    test "pool #{pool_size}: Untrack/4 results in all ids being untracked",
+         %{server: server} do
       topics = for i <- 1..100, do: "topic_#{i}"
       for t <- topics do
         {:ok, _ref} = Tracker.track(server, self(), t, "me", %{a: "b"})
@@ -143,5 +185,16 @@ defmodule Phoenix.Tracker.PoolTest do
 
       for t <- topics, do: assert Tracker.list(server, t) == []
     end
+
+    @tag pool_size: pool_size
+    test "pool #{pool_size}: count/1 returns number of entries across all shards",
+    %{server: server} do
+      topics = for i <- 1..100, do: "topic_#{i}"
+      for t <- topics do
+        {:ok, _ref} = Tracker.track(server, self(), t, "me", %{a: "b"})
+      end
+
+      assert Tracker.size(server) == 100
+    end
   end
 end
diff --git a/test/phoenix/tracker/shard_replication_test.exs b/test/phoenix/tracker/shard_replication_test.exs
index 0a6fed5e..ae505356 100644
--- a/test/phoenix/tracker/shard_replication_test.exs
+++ b/test/phoenix/tracker/shard_replication_test.exs
@@ -244,6 +244,8 @@ defmodule Phoenix.Tracker.ShardReplicationTest do
     assert %{@node1 => %Replica{status: :up}} = replicas(shard)
     assert [{"local1", _}, {"node1", _}] = list(shard, topic)
     assert [{"local1", _}, {"node1", _}] = dirty_list(shard, topic)
+    assert [_] = Shard.dirty_get_by_key(shard, topic, "local1")
+    assert [_] = Shard.dirty_get_by_key(shard, topic, "node1")
 
     # nodedown
     Process.unlink(node_pid)
@@ -252,9 +254,13 @@ defmodule Phoenix.Tracker.ShardReplicationTest do
     assert %{@node1 => %Replica{status: :down}} = replicas(shard)
     assert [{"local1", _}] = list(shard, topic)
     assert [{"local1", _}, {"node1", _}] = dirty_list(shard, topic)
+    assert [_] = Shard.dirty_get_by_key(shard, topic, "local1")
+    assert [_] = Shard.dirty_get_by_key(shard, topic, "node1")
 
     :timer.sleep(@permdown + 2*@heartbeat)
     assert [{"local1", _}] = dirty_list(shard, topic)
+    assert [_] = Shard.dirty_get_by_key(shard, topic, "local1")
+    assert [] = Shard.dirty_get_by_key(shard, topic, "node1")
   end
 
 
diff --git a/test/phoenix/tracker/shard_test.exs b/test/phoenix/tracker/shard_test.exs
index f6338af2..169126a3 100644
--- a/test/phoenix/tracker/shard_test.exs
+++ b/test/phoenix/tracker/shard_test.exs
@@ -13,4 +13,45 @@ defmodule Phoenix.Tracker.ShardTest do
     assert Phoenix.Tracker.Shard.init([nil, nil, opts]) ==
       {:error, "permdown_period must be at least larger than the down_period"}
   end
+
+  defmodule TestTracker do
+    use Phoenix.Tracker
+    def init(state), do: {:ok, state}
+    def handle_diff(_diff, state), do: {:ok, state}
+  end
+
+  describe "size/1" do
+    test "returns 0 when there are no entries in the shard" do
+      tracker = TestTracker
+      name = :"#{inspect(make_ref())}"
+      shard_name = Phoenix.Tracker.Shard.name_for_number(name, 1)
+      given_pubsub(name)
+      opts = [pubsub_server: name, name: name, shard_number: 1]
+      {:ok, _pid} = Phoenix.Tracker.Shard.start_link(tracker, %{}, opts)
+
+      assert Phoenix.Tracker.Shard.size(shard_name) == 0
+    end
+
+    test "returns number of tracked entries in the shard" do
+      tracker = TestTracker
+      name = :"#{inspect(make_ref())}"
+      shard_name = Phoenix.Tracker.Shard.name_for_number(name, 1)
+      given_pubsub(name)
+      opts = [pubsub_server: name, name: name, shard_number: 1]
+      {:ok, pid} = Phoenix.Tracker.Shard.start_link(tracker, %{}, opts)
+
+      for i <- 1..100 do
+        Phoenix.Tracker.Shard.track(pid, self(), "topic", "user#{i}", %{})
+      end
+
+      assert Phoenix.Tracker.Shard.size(shard_name) == 100
+    end
+
+    defp given_pubsub(name) do
+      size = 1
+      {adapter, adapter_opts} = Application.get_env(:phoenix_pubsub, :test_adapter)
+      adapter_opts = [adapter: adapter, name: name, pool_size: size] ++ adapter_opts
+      start_supervised!({Phoenix.PubSub, adapter_opts})
+    end
+  end
 end
diff --git a/test/phoenix/tracker/state_test.exs b/test/phoenix/tracker/state_test.exs
index 081bbff4..9f7f4eb2 100644
--- a/test/phoenix/tracker/state_test.exs
+++ b/test/phoenix/tracker/state_test.exs
@@ -409,4 +409,36 @@ defmodule Phoenix.Tracker.StateTest do
       end)
     end)
   end
+
+  describe "size/1" do
+    test "returns 0 for empty state" do
+      shard_name = :shard
+      State.new(:s1, shard_name)
+      assert State.size(shard_name) == 0
+    end
+
+    test "returns size of the values tables" do
+      shard_name = :shard
+      state = State.new(:s1, shard_name)
+
+      Enum.reduce(1..100, state, fn i, acc ->
+        State.join(acc, self(), "lobby", "user#{i}", %{})
+      end)
+
+      assert State.size(shard_name) == 100
+    end
+
+    test "leaves are accounted for in the returned size" do
+      shard_name = :shard
+      state = State.new(:s1, shard_name)
+
+      state = Enum.reduce(1..100, state, fn i, acc ->
+        State.join(acc, self(), "topic#{i}", "user#{i}", %{})
+      end)
+
+      State.leave(state, self(), "topic1", "user1")
+
+      assert State.size(shard_name) == 99
+    end
+  end
 end