[mythtv-users] Idea for Listings Data

Rod Smith mythtv at rodsbooks.com
Mon Jun 25 23:56:43 UTC 2007


On Monday 25 June 2007 19:02, Matt Mossholder wrote:
>
> On first glance I was inclined to agree with the detractors of using
> DNS to host the data. However, a little research shows this may not be
> as obvious as we all thought. Here's  a quote [1] from zeroconf.org
> about DNS TXT records (the type we would use for a DNS based listings
> service):
>
> "General format rules for DNS TXT records

I'd forgotten about TXT records. Still....

> Given this, it seems like
> DNS TXT records may actually be an even better solution than NNTP...
> consider the following:
>
>         * DNS is pretty much a requirement for all ISPs, while NNTP
> isn't as
> well supported anymore (e.g. ISPs blocking access).

I'm not sure this is really an issue, for two reasons:

1) There was *ONE* post that claimed an ISP (Comcast, IIRC) was actively
   blocking NNTP access. I did a Google search and couldn't turn up
   anything, and the original poster of that claim hasn't posted more
   details. Thus, I'm inclined to skepticism on this claim. If confirmation
   and more details emerge, though, I'm quite willing to listen.

2) It seems to me that using the FULL DNS hierarchy for distributing
   guide data might be considered abusive, assuming it would work at
   all. To the best of my knowledge, services that use DNS for other
   purposes, such as spam "blackhole lists," do so by setting up a
   dedicated DNS server to handle the job. If you were to do it this
   way it might make more sense, but then there'd be little or no
   advantage compared to doing it via HTTP.

>         * DNS records get cached by practically every ISP in the world,
> NNTP is
> fading away, if only because people have some many different
> alternatives (My take, at least. Tell me if I am wrong).

NNTP is less prominent than it once was, but it's still very active. It's my 
impression (I could be wrong) that most ISPs still offer Usenet access as 
part of their basic packages, even if few people know what it is. Some have 
dropped it or charge extra for it, and that's a minus; and if that trend 
continues, it'll become a big minus. In the worst-case scenario (Usenet 
collapses into dust), we'd then need to set up our own NNTP server and 
convert the data distribution into a centralized affair. It would then work 
much like having a centralized HTTP server to do the job.

>         * DNS zone serial numbers and TTL could be used to handle record
> updates. TTL could be used to minimize the need to re-request data on a
> per-record basis, and the actual record TTL could be set based on the
> historical rate of change for the given channel (e.g. changes to channel
> X always occur more than 24 hours before broadcast, while channel Y is
> changing the schedule up to the current hour). If we were really spiffy,
> we could set the TTL of each returned request from the primary DNS
> server, so that they expire within, say, 2 hours of the air time for the
> show.

Unfortunately, it's been my experience that many DNS servers ignore TTL 
values, so I'm not sure this would really buy anything -- at least, not 
reliably.

-- 
Rod Smith
http://www.rodsbooks.com


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