@Override
  public Chunk getNewExternalChunk(int size) {
    int allocSize = size + ChunkCreator.SIZEOF_CHUNK_HEADER;
    if (allocSize <= ChunkCreator.getInstance().getChunkSize()) {
      return getNewExternalChunk(ChunkCreator.ChunkType.DATA_CHUNK);
    } else {
      Chunk c = this.chunkCreator.getJumboChunk(size);
      chunks.add(c.getId());
      return c;
    }
  }
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