Delete a room's messages in a job, one transaction each

Room#destroy destroyed every message inside the room's own
transaction, which holds SQLite's write lock until the last one: on a
room with many messages, every other write in the app waited and
failed. The request now takes the room away from its members and
leaves the rest to Room::DestroyJob, which destroys the messages one
at a time, each in its own short transaction, and then the room.

An open room is closed in the request, so that someone who joins the
account before the job ends isn't given it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bj8KnxpTf9sj2Ysa8aLAVa

test/controllers/rooms/directs_controller_test.rb

@@ -25,8 +25,10 @@ class Rooms::DirectsControllerTest < ActionDispatch::IntegrationTest
     sign_in :kevin
 
     assert_difference -> { Room.count }, -1 do
-      delete rooms_direct_url(rooms(:david_and_kevin))
-      assert_redirected_to root_url
+      perform_enqueued_jobs do
+        delete rooms_direct_url(rooms(:david_and_kevin))
+        assert_redirected_to root_url
+      end
     end
   end
 

test/controllers/rooms_controller_test.rb

@@ -83,11 +83,23 @@ class RoomsControllerTest < ActionDispatch::IntegrationTest
   test "destroy" do
     assert_turbo_stream_broadcasts :rooms, count: 1 do
       assert_difference -> { Room.count }, -1 do
-        delete room_url(rooms(:designers))
+        perform_enqueued_jobs { delete room_url(rooms(:designers)) }
       end
     end
   end
 
+  test "destroy takes the room away from its members at once and leaves its messages to a job" do
+    room = rooms(:designers)
+
+    assert_enqueued_with(job: Room::DestroyJob, args: [ room ]) do
+      assert_no_difference -> { Message.count } do
+        delete room_url(room)
+        assert_redirected_to root_url
+      end
+    end
+    assert_empty room.memberships.reload
+  end
+
   test "destroy only allowed for creators or those who can administer" do
     sign_in :jz
 
@@ -99,7 +111,7 @@ class RoomsControllerTest < ActionDispatch::IntegrationTest
     rooms(:designers).update! creator: users(:jz)
 
     assert_difference -> { Room.count }, -1 do
-      delete room_url(rooms(:designers))
+      perform_enqueued_jobs { delete room_url(rooms(:designers)) }
     end
   end
 

test/models/room_test.rb

@@ -30,8 +30,54 @@ class RoomTest < ActiveSupport::TestCase
     assert Rooms::Closed.new.closed?
   end
 
+  test "an open room destroyed later lets no one in who joins the account before the job runs" do
+    room = rooms(:pets)
+
+    room.destroy_later
+    newcomer = User.create!(name: "Newcomer", email_address: "newcomer@example.com", password: "secret123456")
+
+    assert_not newcomer.memberships.exists?(room_id: room.id)
+    perform_enqueued_jobs only: Room::DestroyJob
+    assert_not Room.exists?(room.id)
+  end
+
+  test "destroying one message at a time leaves nothing of the room behind" do
+    room = rooms(:designers)
+    searchable = room.messages.create!(body: "Kept in the search index", creator: users(:david))
+    searchable.attachment.attach io: StringIO.new("hello"), filename: "hello.txt", content_type: "text/plain"
+    message_ids = room.messages.ids
+    assert Boost.where(message_id: message_ids).exists?
+    assert_equal 1, search_index_rows(searchable)
+
+    room.destroy_one_message_at_a_time
+
+    assert_not Room.exists?(room.id)
+    assert_empty Message.where(id: message_ids)
+    assert_empty Boost.where(message_id: message_ids)
+    assert_empty ActionText::RichText.where(record_type: "Message", record_id: message_ids)
+    assert_empty ActiveStorage::Attachment.where(record_type: "Message", record_id: message_ids)
+    assert_enqueued_jobs 1, only: ActiveStorage::PurgeJob
+    assert_equal 0, search_index_rows(searchable)
+  end
+
+  test "each message is destroyed in its own transaction, so other writes get through in between" do
+    room = rooms(:designers)
+    messages = room.messages.count
+    transactions = 0
+    count_transactions = ->(*, payload) { transactions += 1 if payload[:sql].start_with?("RELEASE SAVEPOINT") }
+
+    ActiveSupport::Notifications.subscribed(count_transactions, "sql.active_record") { room.destroy_one_message_at_a_time }
+
+    assert_equal messages + 1, transactions
+  end
+
   test "default involvement for new users" do
     room = Rooms::Closed.create_for({ name: "Hello!", creator: users(:david) }, users: [ users(:kevin), users(:david) ])
     assert room.memberships.all? { |m| m.involved_in_mentions? }
   end
+
+  private
+    def search_index_rows(message)
+      Message.connection.select_value("select count(*) from message_search_index where rowid = #{message.id}")
+    end
 end