[aur-dev] Making the AUR package list more useful

[Lukas Fleischer]

On Sat, 30 Apr 2016 at 18:16:54, Dave Reisner wrote:
> Hrmm, I don't know that this is an equal comparison. Here's my
> perception of the current world:
> 
> pacman relies on distribution of the *entire* DB to mirrors around the
> world. Due to the tiered mirror system, you can basically only rely on
> eventual consistency of tier N>0 with tier 0, but the DBs at any given
> point in time should be consistent with themselves (i.e. assuming
> they're well-behaved, they won't advertise packages which they don't
> have). In addition to the sync tarballs, pacman relies on a local
> database which it mutates as packages are installed, upgraded, and
> removed.
> 

Yeah, as I mentioned further below, providing the full database might be
a long-term goal.

Are the mirrors part of the basic concept behind pacman? I always had
the impression they primarily exist to improve download performance. One
could also distribute the database among servers all over the world and
allow clients to perform remote procedure calls on each of them. We
could introduce those mirrors to the AUR as well, independent of whether
the database is transferred to the clients or not.

> pacman has reduced functionality when it has no reachable mirror -- it's
> still capable of removing packages, modifying the local DB (to adjust
> install reasons), and install packages which are present in a file
> cache.
> 

I am not sure I follow. How are orthogonal features relevant to the
discussion of whether the sync DB should be copied to the clients or
accessed via requests to a server? It really shouldn't matter which
additional operations on other objects are supported (and even if it
does, there are clients like yaourt which provide a similar interface).
The only thing I can think of in this context is that due to copying the
database, one can perform queries on the sync database while being
offline (i.e. if you want to find out the name of a package you cannot
remember using -Ss). The AUR would benefit from that as well.

> In contrast, the AUR currently only offers an API to support adhoc
> queries. There are no mirrors, and the RPC interface offers strong
> consistency with the contents of the AUR. I think we can agree that in
> the current form, packages.gz and pkgbases.gz files aren't very useful
> as they tend to lag too far behind reality.
> 

Of course. Which is why I started this thread (even though, actually, I
do not think it is *too* bad to lag an hour or two behind; it should not
matter in 99.9% of the use cases).

> AUR clients currently have a hard dependency on the network. If they
> cannot reach the AUR, they cannot do anything useful.
> 

Yeah, again, the same would apply to pacman if we split the sync
operations into a separate utility as we do in the case of the AUR.
Conversely, there is yaourt providing the pacman interface and there are
other AUR helpers that cannot download a source package but still
build/install a downloaded package when you are offline.

I might be missing something...

> Your proposal to make the pkgname/pkgbase tarballs more closely
> consistent doesn't change the network dependency. All it seems to do is
> offload the ability to perform more precise searching to the client,
> *if* they choose to implement it. I'm suggesting that the server should
> do this, such that we have a single implementation which *everyone* can
> take advantage of. Not just clients of the RPC interface, but the web UI
> as well.
> 

Having the web UI make extensive use of the RPC interface is a good
argument against moving towards my suggestions indeed. However, that
would mean we fundamentally change the principles aurweb is currently
built upon. Everything should work without any annoyances with JS
disabled and using only a text-mode browser. Maybe that is too
old-fashioned thinking; maybe even among Arch users, only few users need
support for that and everyone else might benefit from a more "modern"
interface...

> Agreed. Regular expressions aren't necessarily what we want to end up
> with. As an alternative, prefix and suffix matching would be
> substantially cheaper, less prone to abuse/dos, and would probably
> fulfill the needs of most people.
> 

True. But then again, there are some use cases for regular expressions
that are not covered by matching prefixes and suffixes and we might,
again, have people requesting support for them (we had people explicitly
requesting regular expression support a couple of times). If we decide
to reject those requests and tell people "Hey, you cannot do that on the
AUR.", this simply means that they will revive their web scrapers and
build their own package name databases based on the web pages, as they
did before we introduced packages.gz. I even did that myself to build
the database for aurdupes (which is another good example that requires
the full set of names to be available locally) before packages.gz was
there. This is Arch after all, and our users become creative when they
are not given the interface they want.

> If you wanted to offer the ability to return just the size of the
> resultset for some advanced search method, you could add another
> parameter to the current search interface which would elide the
> 'results' list in the reponse JSON. You already have a 'resultcount'
> field with the size.
> 

That is what I meant. We need to change the interface for every feature
request that pops up.

> > * Directly publish all the information required to answer all possible
> >   requests. Let the clients do whatever they want. Currently, we only
> >   provide package names but in the future, this could be extended to a
> >   more complete database like the one pacman uses.
> 
> This has the same problems as the current gz files -- you can only
> offer eventual consistency. It also only scales well if you can
> distribute the load in the same way that pacman does with a tiered
> mirror system. This comes with a non-zero maintenance cost.
> 

True. If it turns out that one server is not sufficient, mirrors need to
be added. However, since we already have all the infrastructure, I
expect the extra maintenance cost to be rather small. I also think that
adding something like zsync support can reduce traffic by orders of
magnitude. This is also something pacman/libalpm itself could benefit
from.

Regards,
Lukas