[pacman-dev] [PATCH] pkgdelta: use highest compression ratio when creating deltas with xdelta3

Allan McRae allan at archlinux.org
Wed Mar 5 19:35:43 EST 2014

On 06/03/14 10:14, Matthias Krüger wrote:
> On 03/06/2014 12:33 AM, Allan McRae wrote:
>> On 06/03/14 09:25, Matthias Krüger wrote:
>>> Looking how pkgdelta works, I found this line
>>>      xdelta3  -q -f -s "$oldfile" "$newfile" "$deltafile" || ret=$?
>>> which seemed to be responsible for the actual delta generation, however
>>>      man xdelta3
>>> revealed that there were different compression levels (0-9) (not sure
>>> which one is default).
>>> To make it short, we could have had smaller deltas since pkgdelta was
>>> introduced!
>>> Examples:
>>> -9          16660K
>>> blender-12:2.69.c7ac0e-1_to_13:2.69.13290d-1-x86_64.delta
>>>   default  17832K
>>> blender-12:2.69.c7ac0e-1_to_13:2.69.13290d-1-x86_64.delta
>>> -9         504K    xbmc-12.3-10_to_12.3-11-x86_64.delta
>>> default  572K   xbmc-12.3-10_to_12.3-11-x86_64.delta
>> How is memory usage changed?   Mainly when regenerating the package from
>> deltas?
> Surprisingly, for blender both runs took ~96MB and 1:50m (+- a second).

I'm assuming that is because that most of the time/memory is used
applying the diff rather than decompressing it given it is quite small.

I know memory usage and speed were issues when it was considered adding
-9 to package compression.  My concern is this also applies to deltas.
However, given the reconstruction of a delta is reasonably
computationally intensive, I'm not sure this restriction applies here.

Anyone else care to comment?


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