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

[Matthias Krüger]

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


The attached patch adds the "-9" option to the line above.

Side note: it might be even more advantageous to use bsdiff instead of 
xdelta3
comparing the /usr/bin/blender binaries of the above versions 
(12:2.69.c7ac0e-1 and 13:2.69.13290d-1) :

xdelta3     10.4M
xdelta3 -9   9.9M
bsdiff          4.7M

,however bsdiff is only for direct diff creation, bsdiff foo1.pkg.tar.xz 
foo2.pkg.tar.xz will create a diff between the archives and not their 
contents, so that'd require further coding which I am unable to do 
(maybe someone else volunteers :) ).

Kind regards, Matthias

-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0001-pkgdelta-use-highest-compression-level-9-when-xdelta.patch
Type: text/x-patch
Size: 1015 bytes
Desc: not available
URL: <http://mailman.archlinux.org/pipermail/pacman-dev/attachments/20140306/fba99e35/attachment.bin>