private LZ4Compressor getCompressor() {
        return level < 7 ? factory.fastCompressor() : factory.highCompressor();
    }
Compresses some data

@param requestedCompression the desired compression type, which will be used if the data is deemed suitable.
                            Not all the existing types are actually supported.
@param data the data to compress. This array is only read by this method.
@param uncompressedSize uncompressedSize the size in bytes of the data array. If this is not present, it is
                        assumed that the size is the same as the data array size, i.e that it is completely
                        filled with uncompressed data.
@return the compression result
@throws IllegalArgumentException if the compression type is not supported
vespajlib/src/main/java/com/yahoo/compress/Compressor.java