Bug#817803: please specify metadata-by-hash

[Colin Watson <cjwatson@debian.org>]

On Tue, Mar 22, 2016 at 11:33:13PM +0100, David Kalnischkies wrote:
> ==> https://wiki.debian.org/RepositoryFormat

Thanks for writing this.  A couple of comments:

> - https://wiki.debian.org/RepositoryFormat#Acquire-By-Hash

I think this should say that clients must fall back to the canonical
locations if by-hash fails, not that they may fall back.  Mirrors
(particularly partial ones) won't necessarily mirror the by-hash files.

> - https://wiki.debian.org/RepositoryFormat#indices_acquisition_via_hashsums_.28by-hash.29

The bit about "two or more previous versions of a file should be
available" is presumably based on apt-ftparchive's behaviour, but it
doesn't necessarily make a lot of sense for a production implementation.
The important thing is to allow enough time that the race between client
and server isn't a problem, including the situation where a mirror
happens to fetch out-of-sync files.  For that, the number of previous
versions is basically irrelevant; what you care about is making sure
that any given version sticks around in by-hash for a certain amount of
time after it ceases to be the current version.  There's no particular
point in keeping old versions just in order to satisfy a numeric
threshold.

Cheers,

-- 
Colin Watson                                       [cjwatson@debian.org]