@Override
  public void close() {
    // active should never be null
    active.close();
    // for snapshot, either it is empty, where we do not reference any real segment which contains a
    // memstore lab, or it is during snapshot, where we will clear it when calling clearSnapshot, so
    // we do not need to close it here
  }
@return The total heap size of cells in this memstore. We will not consider cells in the
        snapshot
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/AbstractMemStore.java