[arch-general] About Arch pkg compress format

Dimitrios Apostolou jimis at gmx.net
Wed May 21 16:24:30 EDT 2008



On Wed, 2008-05-21 at 19:39 +0200, Jan de Groot wrote:
> What's the memory usage when unzipping an LZMA file? Is it much higher
> than the needs of gzip? We already have problems supporting low-memory
> systems with our installer, adding a compression algorithm that eats
> more memory will cause even more problems for these systems.

Yes it eats more memory in comparison to gzip, at least when high
compression is chosen. But still the memory it uses is not much. From
the official site of the LZMA utils: 

http://tukaani.org/lzma/benchmarks

RAM usage on decompression
	gzip		bzip2		lzmash		lzmash -e
1	<1 MB		1 MB		 1 MB		 -
2	<1 MB		2 MB		 2 MB		 -
3	<1 MB		2 MB		 1 MB		 1 MB
4	<1 MB		2 MB		 2 MB		 2 MB
5	<1 MB		3 MB		 3 MB		 3 MB
6	<1 MB		3 MB		 5 MB		 5 MB
7	<1 MB		3 MB		 9 MB		 9 MB
8	<1 MB		4 MB		17 MB		17 MB
9	<1 MB		4 MB		33 MB		33 MB

The memory usage of lzma stays competitive with bzip2 when files have
been compressed with "lzmash -6" or with a smaller option. The files
compressed with the default "lzmash -7" can still be decompressed, even
on machines with only 16 MB of RAM, but sometimes you don't have even
that much memory available. If you compress with "lzmash -8" or "lzmash
-9", you should think if the users need to be able to decompress your
files also on "ancient" computers.


I fully understand the license problem and personally I am pretty happy
with the gzip algorithm, I am just pointing facts so that a technically
correct conclusion is reached. 


Dimitris






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