/// <summary>
/// <para>
/// Keep the current remote scanner alive on the Tablet server for an
/// additional time-to-live. This is useful if the interval in between
/// <see cref="MoveNextAsync"/> calls is big enough that the remote
/// scanner might be garbage collected. The scanner time-to-live can
/// be configured on the tablet server via the --scanner_ttl_ms
/// configuration flag and has a default of 60 seconds.
/// </para>
/// <para>
/// This does not invalidate any previously fetched results.
/// </para>
/// <para>
/// Note that an exception thrown by this method should not be taken as
/// indication that the scan has failed. Subsequent calls to
/// <see cref="MoveNextAsync"/> might still be successful, particularly
/// if the scanner is configured to be fault tolerant.
/// </para>
/// </summary>
/// <param name="cancellationToken">The cancellation token.</param>
public Task KeepAliveAsync(CancellationToken cancellationToken = default)
{
if (_closed)
{
return(Task.FromException(
new Exception("Scanner has already been closed")));
}
if (Tablet is null)
{
// Getting a null tablet here without being in a closed state
// means we were in between tablets. If there is no scanner to
// keep alive, we still return success.
return(Task.CompletedTask);
}
var rpc = GetKeepAliveRequest();
return(_client.SendRpcAsync(rpc, cancellationToken));
}