code: public void setLargestKey(int chunkIdx, byte[] largestKeyInChunk) {
          maxKeyPerChunk[chunkIdx] = largestKeyInChunk;
          filledUpTo = Math.max(filledUpTo, chunkIdx);
          indexBuffer.position(chunkIdx * keySize);
          indexBuffer.put(largestKeyInChunk);
      }
docs: Sets a new largest key in the chunk with the given index.
  
  @param chunkIdx
  @param largestKeyInChunk