private void init(final long firstTimestamp, final T firstValue) {
    lastStoredTimestamp = firstTimestamp;
    lastStoredValue = firstValue;
  }
The last stored time and value we compare current point against lastReadTimestamp and
lastReadValue
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/pipe/processor/downsampling/changing/ChangingValueFilter.java