requires all optimizer variables to be created at the first
        `apply_gradients()` or `minimize()` call. If your workflow calls
        optimizer to update different parts of model in multiple stages,
        please call `optimizer.build(model.trainable_variables)` before the
        training loop.
    *   **Performance regression on `ParameterServerStrategy`.** This could be

                                    type: string
                                  caCrl:
                                    description: 'OPTIONAL: The path to the file containing
                                      the certificate revocation list (CRL) to use
                                      in verifying a presented server certificate.'
                                    type: string

                                    type: string
                                  caCrl:
                                    description: 'OPTIONAL: The path to the file containing
                                      the certificate revocation list (CRL) to use
                                      in verifying a presented server certificate.'
                                    type: string