Yum plugin for prioritize providers [was Re: Fwd: MariaDB replacing MySQL]

[Honza Horak]

I'd like to discuss the topic about virtual provides in a general 
context (not related to MySQL->MariaDB replacement) to find out what 
actually is a consensus in Fedora about an issue when "two packages 
provide the same (not only) virtual symbol" -- particularly what package 
maintainers could/should depend on.

On 03/15/2013 04:22 PM, James Antill wrote:
> On Wed, 2013-03-13 at 18:08 +0100, Honza Horak wrote:
>
>> >I've spent some time deep in yum and it seems to be better than I
>> >thought now. First, the magic about choosing one provider from more
>> >alternatives is not so dark any more (it was worse few years before) --
>> >it's actually documented at [1] now.
>   It's documented what the current version of yum does, and it's
> documented mostly for information purposes ... if you want to install
> "XYZ" and that is provided by "FOO" and "BAR" then installing either is
> correct (even if it's not what you want).
>

That's probably how it should work eventually, but I believe we should 
also be *sure* what will be installed in case nobody requires either FOO 
nor BAR explicitly -- something like distribution-wide default.

Currently, we can follow the steps how scores of providers are count 
[1]. However, since you wrote "it's documented mostly for information 
purposes", the question is -- can we depend on it?


Let me elaborate that a bit more. If we can depend on it, it means it is 
defined somehow -- so it would make sense also to re-define that 
behavior by user if there's a reason for that (i.e. let users to choose 
one of the provider).

The idea I've in my mind is to achieve this by a yum plugin (which would 
use compare_providers hook), which would basically adjust scores for 
possible providers according to a config file.

In case of MySQL/mariadb (just for demonstration) the config file would 
contain say:
     MySQL	+10000
     mariadb	-10000
which would tell yum to prioritize MySQL.

I'm sure that there are several other use cases for such utility. It 
would bring a bit more complexity on the one hand, but would decrease 
ambiguity in specific cases on the other hand.

Any ideas about such tool/plugin?

Cheers,
Honza

[1] http://yum.baseurl.org/wiki/CompareProviders