[CentOS] problems with yum_priorities on CentOS5/RHEL5

Hello,

Many of you will have read this page, with its (somewhat ambiguous) endorsement
of yum_priorities:

 http://wiki.centos.org/AdditionalResources/Repositories/RPMForge

As I gather has been stated before on the centos list [1], that quote stops
short of outlining what exactly is wrong with yum_priorities (YP) and why it's
the best solution.  In fact it goes on to say:

> as of yet, no real world problems have been reported with regard to the
> 'yum-priorities' plugin

Some (I hope, constructive) comments which might help users of yum/YP to avoid
surprises:

- The above statement should be altered, since it obviously isn't true
  (Judging both from comments in [1] and my own experience in [2])

- Perhaps it could explain how YP works and when it doesn't with an example?
  (I have one you are welcome to copy in [2].)

- Could the above page incorporate, or at least link to the useful information
  at the bottom of the page here:

  http://wiki.centos.org/PackageManagement/Yum/Priorities

- Could it also mention somewhere quite visible that yum_priorities is not
  available on RHEL5 so any solutions using YP it will just not work there?


I'd also like to know more about why YP cannot be made available on RHEL, but I
guess this is not the place to ask.

Plus I've noticed a couple of features of yum + YP which aggravate the
shortcomings - again this is probably not the place, but I'll mention them
anyway, as a heads-up to other users.

 1. yum check-updates and yum update do *not* warn you of an impending
    unresolved dependency caused by YP hiding the required package.

It seems the only way to find out is if you go ahead and try and perform the
update, which potentially leaves you with one or more broken packages.

This seems a serious flaw that should be fixed.

 2. Not only do higher priority packages totally eclipse lower priorities,
    whatever version, but yum_priorities also makes it seem like they aren't
    even present.

When a dependency is eclipsed, yum queries with --showduplicates will tell you
there *is* no package which satisfies the missing requirement, making it look
like the repository is broken.

You have to disable all plugins to get the correct answer:

 $ yum --showduplicates --noplugins list perl-Archive-Tar



Finally, I'd like to ask if there have been any developments, or new advice
anyone can offer on the topic, since November 2009?

Thanks,

Nick



1. http://thread.gmane.org/gmane.linux.centos.general/86563

2. An example of when yum_priorities bites included here:
 http://www.noodlefactory.co.uk/~nick/wu-lee/Notes/YumPrioritiesPitfalls

Comments welcomed.