thandy repository mirrorability

[coderman]

On Wed, Aug 4, 2010 at 9:03 AM, Peter Palfrader <peter at palfrader.org> wrote:
> ...
> I've been wondering about mirrorability for when we start using thandy
> for real.  That is, what happens when a user accesses a mirror that is
> in the process of updating its files.
> ...
> So, from a quick look at thandy and without knowing much about it, it
> appears as if thandy will suffer from much of the same problems.  The
> timestamp.txt file looks like one that's particular problematic.  Is
> this correct or is there some clever scheme that avoids the desync
> problems while a mirror update is in progress?

yes, this will have a similar issue. caveat being that at least one
repository has all the files needed, so the client will retry / resume
until success. (not always using a mirror like Debian)

this introduces other issues as one pet peeve of mine during the "use
Thandy as network installer" experiment was that an on-demand network
install would delay a while on failed attempts, while you really want
it to try again quick or bail out.


> Should we worry about this and try to see if we can come up with some
> clever schemes that mitigate or avoid the issue?

i am inclined to say ignore this unless it becomes a problem for these reasons:

- most Thandy clients will be doing background updates, and won't care
if they have to cycle to the next mirror because the current file is
incomplete or missing.

- the HTTP 1.1 resume capability in Thandy means even a partial file
can be useful, so avoiding these is not necessary and may actually be
counter-productive.

note that my understanding of Thandy is rusty, and out of date.
hopefully Nick or others will correct my misstatements :)