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Re: yum-presto not on by default



On Wed, Sep 23, 2009 at 4:20 PM, James Antill <james fedoraproject org> wrote:
> On Wed, 2009-09-23 at 15:22 +0300, Jonathan Dieter wrote:
>> On Wed, 2009-09-23 at 10:49 +0200, drago01 wrote:
>> > On Wed, Sep 23, 2009 at 10:51 AM, Michal Schmidt <mschmidt redhat com> wrote:
>> > > Dne Wed, 23 Sep 2009 07:04:23 +0300 Jonathan Dieter napsal(a):
>> > >> https://bugzilla.redhat.com/show_bug.cgi?id=524720
>> > >> https://bugzilla.redhat.com/show_bug.cgi?id=524982
>> > >>
>> > >> ...
>> > >>
>> > >> The second one has to do with the fact that when rebuilding the rpms,
>> > >> we have to recompress the data, and xz compression is over 10x slower
>> > >> than gzip.
>> > >
>> > > Do I understand it right that yum-presto compresses the data and then
>> > > passes them to rpm which decompresses them back again?
>> > > Why? Is it because it's currently the only way to verify
>> > > checksums/signatures?
>> >
>> > We had a IRC discussion about this yesterday ... it is not yum-presto
>> > but delta rpm and it does not make sense at all.
>> > It should just create uncompressed rpms (assuming rpm can handle them
>> > which it should) ...according to Seth yum does not care whether the
>> > rpms are compressed or not.
>> >
>> > So yes the compression is a useless step here.
>>
>> As I think may have been mentioned elsewhere, the *only* problem is that
>> the rpm signatures must match and the signatures are over the
>> *compressed* rpm.
>
>  No, we have at least 3 problems I think:
>
> 1. Nobody wants to download uncompressed rpms, if they don't have
> presto.
>
> 2. gig signature is over the rpm data (and thus. is over compressed
> data).
>
> 3. createrepo sha256 data is over the entire rpm (and thus. is over
> compressed data).
>
> ...but to me this is all a _problem_in_xz_, not presto/deltarpms. If
> nobody can fix xz before F12 GA then IMNSO we should revert the
> compression to something that works ... the minor savings in xz
> compression isn't worth as much as delta's.

Does not matter which compression algorithm we use creating a
compressed rpm just to uncompressed it again shortly after that is a
waste of cycles/power/time.
As for the GPG signature ... can't the drpm itself be signed?
So we would only need to check that, rather than the rebuilt rpm if we
don't trust the files on the disk we already lost anyway (box is
compromised).


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