private void init(final long firstTimestamp, final T firstValue) {
    upperDoor = Double.MIN_VALUE;
    lowerDoor = Double.MAX_VALUE;

    lastReadTimestamp = firstTimestamp;
    lastReadValue = 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/sdt/SwingingDoorTrendingFilter.java