@Override
  public ExtendedCell copyCellInto(ExtendedCell cell) {
    // See head of copyBBECellInto for how it differs from copyCellInto
    return (cell instanceof ByteBufferExtendedCell)
      ? copyBBECellInto((ByteBufferExtendedCell) cell, maxAlloc)
      : copyCellInto(cell, maxAlloc);
  }
Its initial value is 1, so it is one bigger than the current count of open scanners which
reading data from this MemStoreLAB.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreLABImpl.java