[clug] Anyone using 'snappy', Google's fast compression?
bob at cs.anu.edu.au
Thu May 12 03:13:58 MDT 2011
On 12/05/11 16:33, David Austin wrote:
> On Thu, May 12, 2011 at 4:26 PM, Mike Carden<mike.carden at gmail.com> wrote:
>>> led me to this GOOG project:
>> Well I hadn't heard of it and it looks interesting.
>> Slightly tangentially, I was reading today about the stream
>> compression employed by LTO 5 tape libraries. It grabs a data block,
>> caches it then has a stab at compressing it. Then it compares the
>> compressed block to the original and writes out the smaller of the two
>> to tape - avoiding the trap of making the data bigger if it was
>> already compressed or is incompressible.
>> This is probably old hat to anyone who has worked with the guts of
>> compression implementations before, but I was struck by its simplicity
>> and usefulness.
> Note that the tape still has to store an extra bit per block to record
> if the compressed or original block is stored. Thus, it can require
> small increases in size.
> There exists no lossless compression algorithm that can reduce
> the size of all inputs (if it did exist, run it on the output again and
If my memory serves (and it demonstrably doesn't so much any more),
according to Paul (paulus) Mackerras, one of the inventors of rsync,
the US Patent Office did issue a patent at one point for an invention
that compresses _any_ N-bit sequence into an N-1 bit sequence. Don't
remember the full story, but I think someone pointed out that this was
effectively impossible and the patent was nullified. Anyone know the
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