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Re: Some ideas/questions about yum



Hi again!

Florian Festi <ffesti redhat com> wrote on ‫جمعه ۲۸ اوت ۰۹، ۱۷:۱۳:۱۰‬:
On 08/28/2009 12:27 PM, Hedayat Vatnakhah wrote:
Now, some ideas:
3. AFAIK, currently yum's primary database file contains information about packages, and all of the files in directories such as /usr/bin and /usr/lib, so that it can resolve package and file level dependencies. Isn't it possible to move file level information outside primary db (e.g. to primary_file_deps.db) and translate internal dependencies from file level dependencies to package level dependencies when creating repositories? (So that provides and requires tables in primary db only contain package references rather than file references?).It might be even possible to do it for dependencies outside repository; for example when creating updates repository, you can introduce fedora repository to createrepo, so it can translate all of the file level dependencies of updates packages also.

Bad idea as you never know all repositories existing. Bad idea because you don't want to recreate all repos when one of them changes. Bad idea because changing the data of the packages in the repo likely to lead to other problems.
You don't need to know about all existing repositories, since you can still resolve file level dependencies. In such cases you'll be forced to download the other file I mentioned (primary_file_deps.db).
I don't see why you'll need to recreate all repos when one of them changes! Sorry :( And its impossible to state anything about the last item.


There have actually been efforts long ago to improve the set of files shipped with the primarydb to lower the need of downloading the filelist while still decrease the number of file shipped in the primarydb. AFAIK they got rejected by yum upstream at that time because the also needed cross repo closures (Although this was much less problematic as what you have suggested here).

4. Even if the above solution is possible and can reduce the size of primary db, it won't solve the main problem: for large repositories, you'll need to download large database files. You'll need to download extra database files on some use cases anyway. So, it can be said that currently yum doesn't scale well.
True.
What do you think about it: we can implement parts of yum at the server side (e.g. a web service), and do queries online. The client can submit queries to online repositories, aggregate the results (+using local repositories by itself) and do appropriate actions. It can also store received data to be used when offline or while they are valid. It'll be completely backward compatible with the current clients: those who use the old method can download repositories themselves, like what they do now.
It is possible to think about further details and design it completely, but I want to know about your opinions about the whole idea.
Web services have the problem that they don't mix well with our mirrors infrastructure of simple and stupid http/ftp/rsync servers largely provided by volunteers. It is also difficult to GPG sign external web services. Because of this the whole traffic of such web services would most likely need to run over Fedora infrastructure.
IMHO, even a single php/python script can provide such a XML RPC service (web service was just an example). Mirrors could get this file just like the other files when syncing. But well, it'll be http only. The GPG sign issue could be problematic, but would you really need to sign the traffic?!


When we think of a Fedora that has grown another order of magnitude (may be 2015) it will become hard to argue against a more centralized solution. Right now we are not at the point where the pain of the local repo db does out weight the complexity of a web service architecture IMHO.
No, I don't want to invite to a centralized solution.


But there is another way to drastically reduce the amount of data that has to be transferred: Delta meta data

The repo data bases could be split up into deltas in a similar way as done with the delta rpms aka presto. As a result the meta data of each package would be downloaded (more or less) exactly once. While this idea is arround for a while an implementation is still missing...
Yes, I know. In fact, at first I decided to start working on that. But you'll still need to download it once (while it's possible to put the Fedora repository's metadata into Fedora DVD!). I though that if the proposed solution works, it would be better than delta metadata files.
Even if the whole client/server idea is considered bad, there might be some other ways of organizing the repository metadata so that yum would still download the data it needs rather than all data. But currently I'm interested to here about this Idea...

Thanks,
Hedayat


Florian


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