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Re: Propose Release Goals (delayed ;) - xz compression



David Goodenough <david.goodenough@btconnect.com> writes:

> The only problem is that on small machines (things like the BeagleBone)
> xz compression requires enough memory that you have to enable swap to
> use dpkg.  Now on a machine with a sensible disk this is not a problem,
> but on a machine where the "disk" is an SD-card it is a disaster.

From the xz manpage:
#                     Preset   DictSize   CompCPU   CompMem   DecMem
#                       -0     256 KiB       0        3 MiB    1 MiB
#                       -1       1 MiB       1        9 MiB    2 MiB
#                       -2       2 MiB       2       17 MiB    3 MiB
#                       -3       4 MiB       3       32 MiB    5 MiB
#                       -4       4 MiB       4       48 MiB    5 MiB
#                       -5       8 MiB       5       94 MiB    9 MiB
#                       -6       8 MiB       6       94 MiB    9 MiB
#                       -7      16 MiB       6      186 MiB   17 MiB
#                       -8      32 MiB       6      370 MiB   33 MiB
#                       -9      64 MiB       6      674 MiB   65 MiB

At the default preset (-6), the required RAM for decompressing is about
9MB. The BeagleBone seems to have 256MB of memory (that's what
Wikipedia says), so 9MB shouldn't be an issue.

And if 9MB is too much for some random board, xz -0 still compresses
better than gzip -9 (or so it should) with only 1MB of DecMem.
-- 
Marius Gavrilescu

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