@Override
  protected void updateMetaInfo(ExtendedCell cellToAdd, boolean succ, boolean mslabUsed,
    MemStoreSizing memstoreSizing, boolean sizeAddedPreOperation) {
    throw new IllegalStateException("Not supported by CompositeImmutableScanner");
  }
Returns a set of all cells in the segment
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/CompositeImmutableSegment.java