[RFE] Cache build results

[voxik]

Since Fedora rel-engs are stubborn and delete the build logs so soon that it makes Koschei almost unusable, I think it is about a time to keep the copies of the files on Koschei side.

[mizdebsk]

Should be doable.

Some thoughts:

• It should be enough to keep logs for one or two builds per package - latest build, and latest successful build (which is possibly and hopefully the same build).
• I checked on random sample (17% of all packages) and gzip-compressed logs for average package take about 289 kiB. Times 8263 packages gives about 2.3 GiB storage required for logs for one builds per package. It's not that much.
• Keeping logs on Koschei would make it easier to implement some sort of automated log analysis.
• We could provide downloadable tarballs of latest logs for all packages (eg. one tarball for latest builds and another one for latest successfull builds).
• Logs or log tarballs don't need to be backed up.

[voxik]

It should be enough to keep logs for one or two builds per package - latest build, and latest successful build (which is possibly and hopefully the same build).

I don't agree with this. For example, I opened this RFE today after I was looking on possible instability of test suite of rubygem-activerecord. In this case, it is useful to have not only the logs of the latest successful, but also the builds of previous failures. Actually the failures might differ, since as far as I know, there was more reasons for them. In this case, it might be also useful to check the statuses of builds in between, mainly to see root.logs what exactly was installed during the build.

But it might be useful to be able to define the policy ... for example be quite aggressive by default, but let the maintainer relax the rules ...

[mizdebsk]

Automated log analysis may be wanted by some users. (CC @ignatenkobrain)

[mizdebsk]

Maybe build logs could be stored in ResultsDB?