Use persistent_term for faster adapter config lookups (#4521)

lib/ecto/repo/registry.ex

@@ -18,9 +18,8 @@ defmodule Ecto.Repo.Registry do
   end
 
   def lookup(repo) when is_atom(repo) do
-    GenServer.whereis(repo)
-    |> Kernel.||(raise "could not lookup Ecto repo #{inspect repo} because it was not started or it does not exist")
-    |> lookup()
+    :persistent_term.get(repo, nil) ||
+      raise "could not lookup Ecto repo #{inspect(repo)} because it was not started or it does not exist"
   end
 
   def lookup(pid) when is_pid(pid) do
@@ -38,13 +37,15 @@ defmodule Ecto.Repo.Registry do
   @impl true
   def handle_call({:associate, pid, name, value}, _from, table) do
     ref = Process.monitor(pid)
+    name && :persistent_term.put(name, value)
     true = :ets.insert(table, {pid, ref, name, value})
     {:reply, :ok, table}
   end
 
   @impl true
   def handle_info({:DOWN, ref, _type, pid, _reason}, table) do
-    [{^pid, ^ref, _, _}] = :ets.lookup(table, pid)
+    [{^pid, ^ref, name, _}] = :ets.lookup(table, pid)
+    name && :persistent_term.erase(name)
     :ets.delete(table, pid)
     {:noreply, table}
   end

lib/ecto/repo/supervisor.ex

@@ -187,9 +187,6 @@ defmodule Ecto.Repo.Supervisor do
 
   @doc false
   def init({name, repo, otp_app, adapter, opts}) do
-    # Normalize name to atom, ignore via/global names
-    name = if is_atom(name), do: name, else: nil
-
     case init_config(:supervisor, repo, otp_app, opts) do
       {:ok, opts} ->
         :telemetry.execute(
@@ -199,6 +196,9 @@ defmodule Ecto.Repo.Supervisor do
         )
 
         {:ok, child, meta} = adapter.init([repo: repo] ++ opts)
+
+        # Normalize name to atom, ignore via/global names
+        name = if is_atom(name), do: name, else: nil
         cache = Ecto.Query.Planner.new_query_cache(name)
         meta = Map.merge(meta, %{repo: repo, cache: cache})
         child_spec = wrap_child_spec(child, [name, adapter, meta])
@@ -221,10 +221,6 @@ defmodule Ecto.Repo.Supervisor do
     end
   end
 
-  defp wrap_child_spec({id, start, restart, shutdown, type, mods}, args) do
-    {id, {__MODULE__, :start_child, [start | args]}, restart, shutdown, type, mods}
-  end
-
   defp wrap_child_spec(%{start: start} = spec, args) do
     %{spec | start: {__MODULE__, :start_child, [start | args]}}
   end