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Re: Specifying How Yum Downloads Updates



On Wed, 2009-04-15 at 09:38 -0500, Chris Adams wrote:
> Once upon a time, Bob Gustafson <bobgus rcn com> said:
> > Yes, I'm concerned about the ADDITIONAL packages removed by yum  
> > because it does not maintain a reference count.
> > 
> > It happened to me - 152 packages were removed. Many were critical to  
> > the operation of my system.
> > A reference counting package manager would not have done that.
> 
> What is this "reference counting" you keep mentioning?  How would it
> have helped?
> 
> You asked yum to do something, it displayed a list of all the actions it
> was going to take as a result, and you said yes.  What else could it
> have done?
> 
> When you tell yum to remove a package that other packages depend on, it
> can either remove all the dependencies, or not remove anything.
> Anything else leaves broken packages in the system.  How would some
> "reference counting" change that?

Suppose you have a package PkgA which requires libAB, libBB, libC

On installation of PkgA, it finds that libAB and libBB are already
installed, having been installed with a previous package PkgB. It does
install libC.

If you now remove PkgA, it finds that it depends on libAB, libBB, libC,
which it displays in a list for the user to decide whether it is ok to
also delete.

If the user says Yes, all of the packages PkgA, libAB, libBB, libC are
deleted, leaving the previously installed package PkgB with missing
libAB, libBB dependencies.

A reference counting scheme would detect that libAB and libBB are also
used by another package and would not delete those two packages. Or
offer to delete them.


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