@Override
  public String toString() {
    return "AppendOnlyLogFactory{" +
           "pageSize=" + pageSize +
           (ensureDataVersion ? ", ensure data version: " + expectedDataVersion : "") +
           ", failInsteadOfRecovery=" + failInsteadOfRecovery +
           ", eagerlyCheckFileCompatibility=" + eagerlyCheckFileCompatibility +
           ", cleanFileIfIncompatible=" + cleanFileIfIncompatible +
           '}';
  }
@Override
  public String toString()