[CentOS] Re: Why is yum not liked by some? -- CVS analogy (and why you're not getting it)

Les Mikesell lesmikesell at gmail.com
Fri Sep 9 19:58:35 UTC 2005

On Fri, 2005-09-09 at 14:22, Mike McCarty wrote:
> > 
> >>Les, what you seem to want is to put a tag on the files so one
> >>can create a snapshot version. A simple date will not do what you
> >>want. I know that you think it will. But I did configuration management
> >>for years, and you just do not have any concept of how difficult
> >>the problem is. You need to think of yum as being a transport agent,
> >>because that's really all it is. Yes, it knows about some dependencies,
> >>but it can't know about everything there is to know.
> > 
> > 
> > Please explain what would go wrong if yum simply ignored the
> > presence of files newer than a specified date.
> Please explain to me how the date of a file describes its contents.
> Until you can tell me how, merely by looking at the date of a file,
> one can know what its contents are, then you haven't shown how
> by using dates one can get yum to do consistent downloads.

What I want is for yum to see the same set of .hdr files that
it did in the prior run on a different machine even though some
more have been added.  I don't care about the contents of those
new ones - I want to pretend they weren't added.

> But, IIRC, you said yourself you wanted *consistency*. And that
> cannot be done simply.

I'm willing to trust the Centos repository maintainers not to
remove existing RPM revs or make arbitrary changes to the
same-named files within the window I need.

> > 
> > The only new thing I'm asking is for it to pretend some new files
> > weren't there.
> The easiest way to do that is not to have those files exist. And
> using a date is not a reliable way to guarantee content.

Yes, I'd prefer a tag, but time seems to move reliably in a single

> > Then I'm missing why yum would make different decisions than it
> > did when the files actually weren't there.
> Perhaps you are using the word "consistent" in a way I don't understand.
> Do you mean "repeatable" or do you mean "consistent"?

I don't understand the difference.  I want yum to make the same
decisions regardless of the possible presence of some new files
in the repository.

> Either way, a file timestamp does not guarantee content.

If the timestamps are correct I don't see how it can fail.

> How can yum know what files you want to ignore, unless it has
> version tags associated, and a named version for the entire
> build?

I want to tell it which ones to ignore by telling it the time
of a prior update that I would like it to repeat on a different
machine.  If it simply discarded the hdr files newer than that
it would be looking at exactly the same input as that prior
run had and should thus make the same decisions.  Note that
a subsequent update does not re-get all the old hdr files, it
just pulls any newly available ones.  I want it to pretend those
weren't there.

  Les Mikesell
    lesmikesell at gmail.com

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