@Override
  public Chunk getNewExternalChunk(ChunkCreator.ChunkType chunkType) {
    switch (chunkType) {
      case INDEX_CHUNK:
      case DATA_CHUNK:
        Chunk c = this.chunkCreator.getChunk(chunkType);
        chunks.add(c.getId());
        return c;
      case JUMBO_CHUNK: // a jumbo chunk doesn't have a fixed size
      default:
        return null;
    }
  }
Get the current chunk, or, if there is no current chunk, allocate a new one from the JVM.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreLABImpl.java