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Default Groups, Default Packages, CD Sets and DVD Size
- From: Jeroen van Meeuwen <kanarip kanarip com>
- To: Development discussions related to Fedora <fedora-devel-list redhat com>
- Subject: Default Groups, Default Packages, CD Sets and DVD Size
- Date: Mon, 11 Aug 2008 17:40:26 +0200
there's a number of issues which you may or may not agree with, and are
very real concerns. I'll first try to explain what the issue is;
The CD sets in Fedora 10 Alpha, but also Fedora 8 and 9 Re-Spins,
require all discs in order to be installed. I say installed, but what I
really mean is next, next, next, finish. Eg., this includes the "Office
and Productivity" shortcut to the office, games and sound-and-video
comps groups of packages.
This problem may need a little more detailed description of 1) CD sets
are composed, and 2) how the installation procedures selects
groups/packages to install -in a default install.
FWIW, when I use the term "default install" in this email, it defines
"next, next, finish" without checking or unchecking any package or group
Also, FWIW, I'm not putting in all the details in composing- and
installing-logic, so that only the bare flow of logic related to the
problem set forth remains (or at least I'm attempting to do so).
== The compose ==
Compose tools get input via a kickstart package manifest, which
basically describes what groups and packages should be available during
the installation. It selects all the relevant groups and packages,
resolves the dependencies (inclusive or exclusive -see PS.), puts these
in a tree and may or may not create a DVD from that tree. In the case of
CD sets however, the packages need to be split over multiple discs and
here's how that works (the process is called package ordering for those
of you who didn't know that already):
From a list of groups, the compose tools first select @core and @base
since these are most commonly (e.g. "always") installed. It resolves
dependencies for the packages selected (e.g. the mandatory and default
packages in the groups @core and @base). The transaction is ordered and
the order in which yum will want to install the packages is spit out.
Then, another set of groups is selected, depsolved, ordered is if it
were for a real transaction, and spit out in the correct order.
This continues until all groups the compose tool knows about are
selected and spit out, and the package ordering process will then spit
out "the remainder of packages".
Note that the next generation of compose tools is going to change this
package ordering process to match the behavior of the installation
procedure, but I'll continue with more about that later.
== The installation procedure ==
By the time the installation procedure has gained the necessary input
wrt. which packages to install, it has also selected a number of default
groups (as well as "Office and Productivity" when performing a default
installation). For this purpose, it uses the "default" (True/False)
attribute in the available -possibly aggregated from multiple
repositories, but not in this case- comps.xml. Given no additional input
during the default installation, these are the groups selected to be
installed (from today's x86_64 rawhide):
Resulting in a required RPM payload (on the media) of 2.88 GB, using
exclusive dependency resolving.
2.88 GB in RPMs spans 5 CDs. This means, that a default installation of
Fedora Rawhide today, when using CDs, would require 5 discs minimum.
== However ==
However, the default installation requires all 7 CDs, because of how the
compose tools resolve dependencies (inclusive) during the compose of the
media, and pull in more then is minimally required to complete the
actual transaction of a default installation. The compose tools do so
for good reason:
- one cannot know what package is the user-preferred package for any
given required capability (eg. for fictive capability 'web-client',
there's firefox, iceweasel, elinks, wget, curl, emacs, emacs, emacs,
foo, bar and baz)
- one cannot predict on what installed system one is performing an
upgrade, and to be able to close the transaction certain considerations
must be met justifying the need for inclusive dependency resolving when
composing the media (set) or installation tree.
- it makes the released media apply to N+X use-cases where the package
set or transaction payload during the installation is controlled in a
more granular fashion then the selection dialogs allow (by means of a
kickstart package manifest maybe?), which I guess applies more to
businesses or advanced users using Fedora then it does to Joe Average users.
Basically what I'm saying is that the 2.88 GB is spread over more then
the minimal amount of discs it would fit on, since the complete package
payload when using inclusive dependency resolving grows to 3.66 GB, or 7
discs. So, the compose process spits out 7 discs, each of which contain
a part of the 2.88 GB sized RPM payload needed for a default installation.
== Next Generation of Package Ordering ==
So, what package ordering is going to do -instead of having a static
list of groups to add to a transaction, resolve, spit out the packages-
is use the "default" parameter to groups in comps.xml as well (and then
instead of exclusive dependency resolving like it does now, move to
inclusive dependency resolving as well). This makes the "which packages
and groups are in a default installation" a little less hard to maintain
and the package ordering will almost automagically match up with
comps.xml (of which the installation procedure also uses the default
parameter to groups!)
== DVD and Sizes ==
This leads me to another concern which may or may not be an immediate
issue but requires attention from those in the decision making chain as
well as generally interested people; the size of the DVD ISO is getting
to it's maximum allowed size (just under 4GB for those who use FAT
systems as their downloaded data partition), providing just a default
(eg. not including anything in addition to the default).
== Advise needed ==
There's several ways this can be solved, but I'm not sure what is the
most advisable (some are not feasible I'm sure, I'm just brainstorming
1) reduce the number of mandatory and default packages per group in
2) reduce the number of groups in comps.xml that have "default" set to True
3) Revisit how comps is formatted; Example: Keep the "default" for
compose decisions, but add an "install" attribute for installation
decision making. Install set to True may require default set to True as
well for the group to even be included on the media.
4) Split the packages that are mandatory or default in comps groups,
into smaller packages providing what the group needs and another set of
smaller packages belonging to the group as to reduce the number of
dependencies needing to be met when the compose or installation
procedure selects a group. See also PS2.
5) Or, compared to 4, revisit the Requires in mandatory and default
packages and the Provides in the packages that provide the required
capabilities so that it abstracts from the requires/provides matching
with too many other packages (related to the inclusive dependency
resolving which will then make for a thinner RPM payload on the composed
6) Have the compose tools as well as the installation procedures not
depend on the default attribute to groups anymore, at all.
Thank you very much for reading this message so far, and please don't
hesitate to ask any questions if I wasn't clear enough in how this works
(though I also hope I didn't overdo it for those who already knew) or
make a remark or two when you think I'm wrong about something ;-)
Ideas and insight on the topic very much appreciated,
Jeroen van Meeuwen
PS. Inclusive dependency resolving is grabbing _all_ packages that
provide a required capability. Exclusive dependency resolving is
grabbing the one best fit (this is YUM dependency resolving). I'm taking
a few shortcuts here but I hope that's OK.
PS2. Selecting all 18 default groups in rawhide results in 79 mandatory
packages, 302 default packages, and (after depsolving) 1386 packages in
total, being a 3.66 GB payload
 the find-default-groups.py run against a rawhide yum configuration
[jmeeuwen ghandalf scripts]$ ./find-default-groups.py -c
3.66 GB (3934874324 archive_size)
79 mandatory packages, 302 default packages, 1386 packages in total
The actual script can be found at
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