Change set_reachable/1 to an upsert

changelog.d/reachability.change

@@ -0,0 +1 @@
+Reduce the reachability timestamp update to a single upsert query

lib/pleroma/instances/instance.ex

@@ -97,13 +97,9 @@ def reachable?(url_or_host) when is_binary(url_or_host) do
   def reachable?(url_or_host) when is_binary(url_or_host), do: true
 
   def set_reachable(url_or_host) when is_binary(url_or_host) do
-    with host <- host(url_or_host),
-         %Instance{} = existing_record <- Repo.get_by(Instance, %{host: host}) do
-      {:ok, _instance} =
-        existing_record
-        |> changeset(%{unreachable_since: nil})
-        |> Repo.update()
-    end
+    %Instance{host: host(url_or_host)}
+    |> changeset(%{unreachable_since: nil})
+    |> Repo.insert(on_conflict: {:replace, [:unreachable_since]}, conflict_target: :host)
   end
 
   def set_reachable(_), do: {:error, nil}

test/pleroma/instances/instance_test.exs

@@ -31,14 +31,6 @@ test "keeps nil `unreachable_since` of existing matching Instance record having
       assert {:ok, instance} = Instance.set_reachable(instance.host)
       refute instance.unreachable_since
     end
-
-    test "does NOT create an Instance record in case of no existing matching record" do
-      host = "domain.org"
-      assert nil == Instance.set_reachable(host)
-
-      assert [] = Repo.all(Ecto.Query.from(i in Instance))
-      assert Instance.reachable?(host)
-    end
   end
 
   describe "set_unreachable/1" do