@Override
  protected ByteBuffer internalDecodeKeyValues(DataInputStream source, int allocateHeaderLength,
    int skipLastBytes, HFileBlockDefaultDecodingContext decodingCtx) throws IOException {
    int decompressedSize = source.readInt();
    ByteBuffer buffer = ByteBuffer.allocate(decompressedSize + allocateHeaderLength);
    buffer.position(allocateHeaderLength);
    ByteBufferUtils.copyFromStreamToBuffer(buffer, source, decompressedSize);

    return buffer;
  }
Just copy data, do not do any kind of compression. Use for comparison and benchmarking.
hbase-common/src/main/java/org/apache/hadoop/hbase/io/encoding/CopyKeyDataBlockEncoder.java