@Override
  protected long indexEntrySize() {
    return ((long) ClassSize.CELL_CHUNK_MAP_ENTRY - KeyValue.FIXED_OVERHEAD);
  }
------------------------------------------------------------------------ C-tor to be used when
new CellChunkImmutableSegment is built as a result of flattening of CSLMImmutableSegment The
given iterator returns the Cells that "survived" the compaction.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/CellChunkImmutableSegment.java