@Override
  public String toString() {
    return String.format("TimeSeriesKey {key: %s timestamp: %s seqNum: %s}", key, timestamp, seqNum);
  }
The store key used in the {@link TimeSeriesStore} to uniquely identify a row.
samza-core/src/main/java/org/apache/samza/operators/impl/store/TimeSeriesKey.java