Bug#944964: dh-make-perl: Module accesses internal dpkg database

[gregor herrmann]

On Tue, 19 Nov 2019 01:15:52 +0100, Guillem Jover wrote:

> Hi!

Hola!
And thanks for looking into this question.
 
> > I've now come up with a first patch (pushed to git) which seems to
> > work and which is not terribly slow.
> > t/DpkgLists.t still passes and takes ~9 seconds; with the original
> > _cat_lists() it was more like 2.5 seconds but well.
> Hmm ouch, I didn't expect it to be that slow. 

Please note that t/DpkgLists.t runs 7 tests, so _cat_lists() is
called 7 times; the speed loss per run is not so bad.

> I've poked a bit, and
> attached are some changes I've got locally that should shave a couple
> of seconds. Will keep looking for further improvements. 

Cool, thanks.

> But I guess
> in the end dpkg-query is just doing more work, as it first needs to
> parse the status db, build all the internal data structures, and then
> build the output according to the format specified.

Right, dpkg-query has to do more than the old implementation which
just read the *.list files.
 
> Maybe I need to look into making «dpkg-query --listfiles» require no
> packages to dump the entire thing like in this case. But I'm not sure
> how common this need is? But much of the involved work above would
> still be done all the same, we'd just skip part of the formatting.

I agree that it's probably not worth the effort, as this use case is
a bit niche, and the speedup would probably be not that enormous.
 

Cheers,
gregor

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