Zsync for Packages files

James Westby jw+debian at jameswestby.net
Fri Jul 17 22:56:09 BST 2009

Mackenzie Morgan wrote:
> On Friday 17 July 2009 1:13:06 pm Max Bowsher wrote:
>> Lars Wirzenius wrote:
>>> I have not compared zsync with pdiffs. Ubuntu does not use pdiffs
>>> because it generates Packages files every hour, and it seems that ruins
>>> the usability of pdiffs.
>> That's interesting - I would have thought that it would simply lead to
>> many small pdiff files being created, but the system overall still
>> working fine. How is the usability damaged?
> (Guessing) Unless you update every hour, the pdiff won't work for you because 
> it's against a newer version than what you've got, maybe?

pdiffs still work in this case, as you keep several around, and then you
can apply each in turn to get from where you are to the current one.

I believe the issue was that applying many pdiffs (either the
implementation or the idea) ended up being slower than just grabbing
the new file when the chain grew to more than a few entries long.
Debian disabled them by default for this reason. Ubuntu creating one
every hour meant that it reached this limit a lot faster than
Debian, and so if Debian didn't want them then Ubuntu certainly didn't.



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