Add a stats agent for storing data from expensive queries.

lib/pleroma/stats.ex

@@ -0,0 +1,38 @@
+defmodule Pleroma.Stats do
+  use Agent
+  import Ecto.Query
+  alias Pleroma.{User, Repo, Activity}
+
+  def start_link do
+    agent = Agent.start_link(fn -> %{} end, name: __MODULE__)
+    schedule_update()
+    agent
+  end
+
+  def get do
+    Agent.get(__MODULE__, fn stats -> stats end)
+  end
+
+  def schedule_update do
+    update_stats()
+    spawn(fn ->
+      Process.sleep(1000 * 60 * 60 * 1) # 1 hour
+      schedule_update()
+    end)
+  end
+
+  def update_stats do
+    peers = from(u in Pleroma.User,
+      select: fragment("?->'host'", u.info),
+      where: u.local != ^true)
+    |> Repo.all() |> Enum.uniq()
+    domain_count = Enum.count(peers)
+    status_query = from p in Activity,
+      where: p.local == ^true,
+      where: fragment("?->'object'->>'type' = ?", p.data, ^"Note")
+    status_count = Repo.aggregate(status_query, :count, :id)
+    Agent.update(__MODULE__, fn _ ->
+      %{peers: peers, domain_count: domain_count, status_count: status_count}
+    end)
+  end
+end