debian.py check for virtual packages is slow

[jacobperron]

In debian.py checking for remaining virtual packages one-by-one in a loop at L189 is quite slow for large lists of packages. This is due to the apt-cache show command. In particular, I'm looking to cut down on build times in some of my pipelines.

I've noticed that calling apt-cache show on packages sequentially is a lot slower than passing all packages at once. Example execution times for 58 packages from the shell:

time cat test_pkgs | xargs -L1 apt-cache show

1m 12.915s

time apt-cache show $(cat test_pkgs)

0m 2.920s

I'm exploring possibilities for enhancement of the Python script.

As an aside, I noticed that packages are checked twice over. Does this have something to do with separating build and run depends?

[Nickolaim]

@jacobperron - is the issue still valid? Pull request #521 touches on this functionality, and I see in the code cmd = ['apt-cache', 'showpkg'] + list(packages) that is probably doing what was requested in the issue.

If it is not the case, please provide a repro, I will be happy to work on it.

[jacobperron]

@Nickolaim Does not appear to be an issue any more. Cheers!