[mythtv-users] Mooting architecture for a DataDirect replacement

[Peter Schachte]

Rod Smith wrote:

>>> I used net news back in the day.  My memories are of out-of-order
>>> messages, replies to messages that never-ever came through, and other
>>> general annoyances.
> 
> For the application under discussion, out-of-order postings don't matter;

If there are multiple updates to the schedule in separate postings, I don't
think this is true.  If there's an update that says that station X is airing
program Y at time Z, and another update sent an hour later that says no, it'll
be at time Q instead, then you don't want to handle them in the wrong order.

I believe the OP suggested we consider requirements for this system.  As much
as I like usenet for discussion forums, I think the requirements for our
purposes here are rather different.  One key requirement for us is that
distribution be reliable; ie, at all times, every subscriber should have the
correct schedule for their lineup as at the time of their last update.  Another
is that if something goes wrong and somehow myth doesn't have the correct
schedule, it should be able to tell, and be able to correct it.  It's hard for
me to see how to satisfy that with NNTP.  If postings get lost or come in out
of order, the schedule winds up wrong.  The problem could be detected if each
posting contain a checksum for the whole lineup after the change in the posting
is applied (not just for that posting).  But if the checksum fails, what can
you do?  If you drop the whole schedule and reread all the postings from the
same host, you'll just get back the same wrong schedule.  You need an authority
to go to to get the correct data.

Someone else suggested bittorrent for this, and it actually has some properties
that make it quite appropriate.  Namely that there is a central authority
anyone can go to to find out what updates have been published (as torrents),
but the data itself can be efficiently downloaded from peers.  And each update
would have a cryptographic hash, so any corruption would be detected.  It's
also friendly to binary data, so the udpates could all be compressed to
decrease bandwidth requirements.

-- 
Peter Schachte              I worry that 10 or 15 years from now, [my child]
schachte at cs.mu.OZ.AU        will come to me and say 'Daddy, where were you
www.cs.mu.oz.au/~schachte/  when they took freedom of the press away from
Phone: +61 3 8344 1338      the Internet?' -- Mike Godwin