Ensure new connections in pool are updated

Author: Schultzer

lib/adapters/postgres.ex

@@ -14,7 +14,11 @@ defmodule SQL.Adapters.Postgres do
   @ssl <<8::32, 80877103::32>>
 
   def start(state) do
-    {:ok, spawn_link(fn -> init(state) end)}
+    pid = spawn_link(fn -> init(state) end)
+    case :persistent_term.get(state.name, nil) do
+      nil -> {:ok, pid}
+      pool -> {:persistent_term.put(state.name, :erlang.setelement(state.scheduler_id, pool, pid)), pid}
+    end
   end
 
   defp to_iodata({:in, m, [{:not, _, left}, {:binding, _, [idx]}]}, format, case, acc) do

lib/application.ex

@@ -14,7 +14,7 @@ defmodule SQL.Application do
     for {name, opts} <- pools do
       pid = Process.whereis(name)
       children = Supervisor.which_children(pid)
-      pids = Enum.map(children, fn {_id, pid, _type, _mod} -> pid end)
+      pids = Enum.reverse(Enum.map(children, fn {_id, pid, _type, _mod} -> pid end))
       :persistent_term.put(name, List.to_tuple(pids))
       :persistent_term.put({name, :oids}, Mix.Tasks.Sql.Get.oids({name, Map.new(opts)}))
       # :persistent_term.put({name, :types}, {Mix.Tasks.Sql.Get.get(key), Mix.Tasks.Sql.Get.columns(key), Mix.Tasks.Sql.Get.enums(key), Mix.Tasks.Sql.Get.oids(key), Mix.Tasks.Sql.Get.functions(key)})

lib/pool.ex

@@ -19,7 +19,7 @@ defmodule SQL.Pool do
       for n <- 1..:erlang.system_info(:schedulers_online) do
         %{
           id: {:conn, n},
-          start: {state.adapter, :start, [struct(state, scheduler_id: n+1, label: :"#{state.name}_#{n}")]},
+          start: {state.adapter, :start, [struct(state, scheduler_id: n, label: :"#{state.name}_#{n}")]},
           restart: :permanent,
           shutdown: 5000,
           type: :worker,

test/integration/postgres_test.exs

@@ -162,4 +162,11 @@ defmodule SQL.Integration.PostgresTest do
     Task.Supervisor.async_nolink(SQL.TaskSupervisor, fun)
     assert_receive ^state
   end
+
+  test "connection pool is self healing" do
+    conn = elem(:persistent_term.get(:default), 0)
+    Process.exit(conn, :shutdown)
+    Process.sleep(50)
+    refute elem(:persistent_term.get(:default), 0) == conn
+  end
 end