Re: [gentoo-dev] New distfile mirror layout

[Michał Górny]

On Sat, 2019-10-19 at 19:24 -0400, Joshua Kinard wrote:
> On 10/18/2019 09:41, Michał Górny wrote:
> > Hi, everybody.
> >
> > It is my pleasure to announce that yesterday (EU) evening we've switched
> > to a new distfile mirror layout.  Users will be switching to the new
> > layout either as they upgrade Portage to 2.3.77 or -- if they upgraded
> > already -- as their caches expire (24hrs).
> >
> > The new layout is mostly a bow towards mirror admins, for some of whom
> > having a 60000+ files in a single directory have been a problem.
> > However, I suppose some of you also found e.g. the directory index
> > hardly usable due to its size.
> >
> > Throughout a transitional period (whose exact length hasn't been decided
> > yet), both layouts will be available.  Afterwards, the old layout will
> > be removed from mirrors.  This has a few implications:
> >
> > 1. Users who don't upgrade their package managers in time will lose
> > the ability of fetching from Gentoo mirrors.  This shouldn't be that
> > much of a problem given that the core software needed to upgrade Portage
> > should all have reliable upstream SRC_URIs.
> >
> > 2. mirror://gentoo/file URIs will stop working.  While technically you
> > could use mirror://gentoo/XX/file, I'd rather recommend finally
> > discarding its usage and moving distfiles to devspace.
> >
> > 3. Directly fetching files from distfiles.gentoo.org will become
> > a little harder.  To fetch a distfile named 'foo-1.tar.gz', you'd have
> > to use something like:
> >
> > $ printf '%s' foo-1.tar.gz | b2sum | cut -c1-2
> > 1b
> > $ wget http://distfiles.gentoo.org/distfiles/1b/foo-1.tar.gz
> > ...
> >
> >
> > Alternatively, you can:
> >
> > $ wget http://distfiles.gentoo.org/distfiles/INDEX
> >
> > and grep for the right path there.  This INDEX is also a more
> > lightweight alternative to HTML indexes generated by the servers.
> >
> >
> > If you're interested in more background details and some plots, see [1].
> >
> > [1] https://dev.gentoo.org/~mgorny/articles/improving-distfile-mirror-structure.html
> >
>
> So the answer I didn't really see directly stated here is, where do new
> distfiles need to go //now//?  E.g., if on woodpecker, I currently cp a
> distfile to /space/distfiles-local.  What is the new directory I need to
> use?  And if mirror://gentoo/${FOO} is going away, for the new distfiles
> target, what would be the applicable prefix to use?
>
> Directly using devspace seems like a bad idea, IMHO.  Once long ago, we all
> got chastised for doing exactly that.  Too much possibility of fragmentation
> as devs retire or package maintainership changes hands.

Today you get chastised for using /space/distfiles-local and not
following policy changes.  The devmanual states that it's deprecated
since at least 2011, and talks of using d.g.o [1].

> I looked at the whitepaper'ish-like writeup, and I kinda don't like using a
> hash-based naming scheme on the new distfiles layout.  I really kind prefer
> breaking the directories up based on the first letter of the distfiles in
> question, factoring case-sensitivity in (so you'd have 52 top-level
> directories for A-Z and a-z, plus 10 more for 0-9).  Under each of those
> directories, additional subdirectories for the next few letters (say,
> letters 2-3).  Yes, this leads to some orphan cases where a distfile might
> live on its own, but from a direct navigation standpoint, it's easy to find
> for someone browsing the distfiles server and easy to predict where a
> distfile is at.
>
> No math, statistical analysis, or deep-rooted knowledge of filesystems
> behind that paragraph.  Just a plain old unfiltered opinion.  Sometimes, I
> need to go get a distfile off the Gentoo mirrors, and being able to quickly
> find it in the mirror root is great.  Having to do hash calculations to work
> out the file path will be *really* annoying.

Your solution still doesn't solve the problem of having 8k-24k files
in a single directory, even if you use 7 letters of prefix.  So it just
creates a lot of tiny directory noise for no practical gain.

[1] https://devmanual.gentoo.org/general-concepts/mirrors/index.html#suitable-download-hosts

-- 
Best regards,
Michał Górny