Background

I have an ETS table where several processes can write concurrently. This table is very very requested, so having a GenServer as a gatekeeper serializing writes is not an option (it can’t hold the load).

Problem

The solution to this, given the GenServer limitations, would be to have each write be atomic. Now, I am aware of update_counter, but there is one problem. My ETS table doesn’t save counters, it saves lists of urls:

  def save_failed_request(url) do
    urls = :ets.lookup(__MODULE__, :failed_urls)

    case urls do
      []  ->
        :ets.insert(__MODULE__, {:failed_urls, [url]})

      [failed_urls: list] ->
        new_list = [url] ++ list
        :ets.insert(__MODULE__, {:failed_urls, new_list})
    end

    {:ok, :saved}
  end

This is the code I currently have to save an URL. Since multiple processes can be calling this function concurrently, multiple processes can be writing in the ETS table under the same key, which is not good.

Question

Is there any ETS function that allows me to make atomic updates on values stored in the table?
Or do I have to use counters ? (because the only atomic operation that exists for updates is update_counter?