default long decMemStoreSize(long dataSizeDelta, long heapSizeDelta, long offHeapSizeDelta,
    int cellsCountDelta) {
    return incMemStoreSize(-dataSizeDelta, -heapSizeDelta, -offHeapSizeDelta, -cellsCountDelta);
  }
Returns The new dataSize ONLY as a convenience
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreSizing.java