[Mageia-discuss] Suggestions for the ISO

andre999 andr55 at laposte.net
Sat Nov 6 19:58:11 CET 2010

Olivier Thauvin a écrit :
> * andre999 (andr55 at laposte.net) wrote:
>>> * andre999 (andr55 at laposte.net) wrote:
>>>> Donald Stewart a écrit :
>>> The problem of delta rpm is the work need to generated alls delta and
>>> the space need on mirrors to host everything.
>>> We must provide delta for each version to the next one:
>>> - main foo-1
>>> - upd  foo-2 D: 1->2
>>>          foo-3 D: 2->3 and 1->3 ?
>>>          foo-4 D: 3->4 and 1->4, 2->4 ?
>> I would make all delta updates relative to the distro release, i.e.
>> - main = foo-1
>> - upd_full = foo-2, foo-3, foo-4, etc
>> - upd_delta = foo-1>2, foo-1>3, foo-1>4, etc
>> without foo 2>3, 2>4, 3>4
>> (so half as many, with 3 updates.)
>> Note that the idea is to retain full update packages, the delta updates
>> being a file-by-file diff of contained files (probably in their own
>> repository).
> That mean people udapting frequently their distribution will not profit
> of delta rpm, then downloading the full rpm as soon they made one
> update.
> Delta rpm will become not so usefull then, except for new install.
Don't think so.  I follow closely changes in Mozilla Seamonkey, for 
example, and changes are very small with each update.  I would say much 
less than 1% of the files, by the space taken.
I think that this is typical.
However, for much smaller programs, it could be that after cumulative 
updates, the delta update is the same size as a full update - but never 
bigger (except maybe a few bytes).
>>> etc...
>>> What if delta 1->4 is bigger than the package itself ? and for 2->4 ?
>> Highly improbable, as I conceive it.
>> If foo-1.rpm contains files fooa foob fooc food, and only foob changes
>> to foob',
>> then full foo-2.rpm contains files fooa foob' fooc food
>> and delta foo-2d.rpm contains only file foob', with the info that this
>> replaces foob.
>> And of course with this model, there is no 2->4.
> Changes between 1->4 will probably be bigger than 2->4 as there is more
> changes between them.
Evidently.  The deltas will tend to become bigger with each update.  But 
remaining generally much smaller than a full update.
>>> Delta rpm is hard to manage (any volunteer to write the tools to manage
>>> this ?) and as bonus, I am not sure it is still compatible with our
>>> current rpm...
>> To create a delta rpm, one only needs the new full version (or the
>> proposed contents), and a script which automatically includes the new
>> files with the references to those replaced.
>> I'm not trying to say it is simple to write - especially since I
>> understand that the current tools are written in Perl - which has a
>> syntax which I barely understand.
>> But I'd be interested in contributing to my ability.
> Nothing deny you to start to work on this and then submit you code. It's
> what I did for the mirrors tools :)
Good idea :)
The arrival of Mageia is motivating me to contribute more, something 
I've always put off doing with Mandriva (except to Bugzilla and forums).
Maybe I can find a language a bit more friendly (to me) than Perl ?
> We'll see when BS and SVN will be ready to merge it if it works.
>>> Just think we don't have an infinite space on mirror. Even the sound
>>> good, please try to estimated the cost it can be per release.
>> I agree it would take more space on mirrors, but as full updates take
>> much less space than the release,
>> delta updates would take considerably less space the full updates.
>> Also, the lower bandwidth to download for users would also benefit the
>> mirrors.
> You know, most of our rpms are less than 10MB, but du -sh is clear, the
> distribution is around 35GB per arch.
> Nothing is really big on mirrors, but the results is.
But if we can reduce 10MB updates to 1MB, that would be a big benefit 
for downloading updates.  Especially for low bandwidth users.
And I think that the % update will likely be much more than that.
Don't forget that commercial updates (often erroneously referred to as 
patches) are often delta (by file) updates, as being proposed.

- André

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