scaling fix: coalesce session push notifications

lib/floof.ex

@@ -95,7 +95,11 @@ defmodule Floof do
           {backlog, sesskey}
 
         {:SessionPushed, sesskey} ->
-          :ok = send_summary(client, :requestpull, Floof.SessionManager.peek(sesskey))
+          sesskeys = coalesce_sesspushes([sesskey])
+          [sesskey | _] = sesskeys
+          dcdids = Enum.map(MapSet.new(sesskeys), &MapSet.new(Floof.SessionManager.peek(&1)))
+          dcdids = Enum.reduce(dcdids, &MapSet.union(&1, &2))
+          :ok = send_summary(client, :requestpull, dcdids)
           {backlog, sesskey}
 
         {:SessionDetached, old_sesskey} ->
@@ -198,6 +202,14 @@ defmodule Floof do
     :ok = Floof.PacketSpool.store_new_multi(backlog)
   end
 
+  defp coalesce_sesspushes(sesskeys) do
+    receive do
+      {:SessionPushed, sesskey} -> coalesce_sesspushes([sesskey | sesskeys])
+    after
+      10 -> sesskeys
+    end
+  end
+
   defp partition_hashes(xs) do
     xs
     |> Floof.DistributorSeen.have_we_multi()

lib/floof/session_manager.ex

@@ -105,7 +105,8 @@ defmodule Floof.SessionManager do
       &case :dets.lookup(&1.dets_file, key) do
         {:error, _} -> []
         items -> Enum.map(items, fn {_, x} -> x end)
-      end
+      end,
+      :infinity
     )
   end