[wix-users] Delta created by pyro much larger than actual differences

[Ben Catterall]

I've recently added the -delta flag when building patches with pyro which
has resulted in smaller patches, but not as small as I was expecting. My
script is as follows:

candle patch.wxs
light patch.wixobj
melt ..\old\project.msi -out old.wixpdb -pdb old\project.wixpdb -x old_bin
melt ..\new\project.msi -out new.wixpdb -pdb new\project.wixpdb -x new_bin
torch -p -xi old.wixpdb new.wixpdb -out diff.wixmst

pyro -delta patch.wixmsp -out patch.msp -t proj1 diff.wixmst

It appears to be one file in particular that's causing problems: The
original and new versions of the file are both around the 100MB mark. Using
our old bdiff-based patcher generates a diff of 15KB, but pyro -delta uses
18MB!! Examining the file with winmerge confirms that there are not 18MB
worth of changes to include.

Is there a way I can improve (reduce) the size of pyro's diff? Is this a
bug in WiX?


Ben