private long cellAfterFlushSize() {
    // make one cell
    byte[] row = Bytes.toBytes("A");
    byte[] val = Bytes.toBytes("A" + 0);
    KeyValue kv = new KeyValue(row, Bytes.toBytes("testfamily"), Bytes.toBytes("testqualifier"),
      EnvironmentEdgeManager.currentTime(), val);

    return toCellChunkMap
      ? ClassSize.align(ClassSize.CELL_CHUNK_MAP_ENTRY + kv.getSerializedSize())
      : ClassSize
        .align(ClassSize.CELL_ARRAY_MAP_ENTRY + KeyValue.FIXED_OVERHEAD + kv.getSerializedSize());
  }
Test big cell size after in memory compaction. (HBASE-26467)
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestCompactingToCellFlatMapMemStore.java