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

Matthias Krüger matthias.krueger at famsik.de
Wed Mar 5 18:25:21 EST 2014

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 


-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 
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

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