training loop.
    *   **Performance regression on `ParameterServerStrategy`.** This could be
        significant if you have many PS servers. We are aware of this issue and
        working on fixes, for now we suggest using the legacy optimizers when
        using `ParameterServerStrategy`.
    *   **Timeout or performance loss.** We don't anticipate this to happen, but
        if you see such issues, please use the legacy optimizer, and file