Path: utzoo!utgpu!water!watmath!clyde!rutgers!husc6!ut-sally!ut-emx!auscso!bigtex!james
From: james@bigtex.uu.net (James Van Artsdalen)
Newsgroups: news.software.b
Subject: Re: Two News feeds
Summary: Delayed ihave/sendme has uses
Message-ID: <827@bigtex.uu.net>
Date: 15 Feb 88 01:27:03 GMT
References: <484@wa3wbu.UUCP>
Organization: F.B.N. Software, Austin TX
Lines: 61
Posted: Sun Feb 14 19:27:03 1988


I have been experimenting with "delayed" ihave/sendme messages recently to use
with backup news feeds.  The impetus for this was a nearly month-long
disruption in the news feed for bigtex due to downtime at an upstream site.

bigtex has a number of PC Pursuit links used for mail around the country.
Because of connection difficulties they aren't generally useful for carrying
news.  However, it is possible to do so, and desirable if there is a major
feed disruption.  The goal is to have the backup PC Pursuit feed kick in
without human intervention.

The regular ihave/sendme isn't quite what is desired, because it gets the
ihave message to the remote system too quickly.  The "regular" path to the
remote system may be a half dozen hops or more, and the direct PC Pursuit
call will often beat the regular route (for messages generated nearby).  The
result is that the remote system gets the ihave before getting the article,
and generates the sendme even though the article is likely to arrive soon
via the regular route.  For example, if I post a message on bigtex in the
evening, it is probable that the ihave would reach remote-sys before the article
itself did via the normal path.

What I have done is slightly modify the sendbatch script in the following
manner:

	if test -n "$DOIHAVE" -a -s /usr/spool/batch/$rmt.ihave
	then
		mv /usr/spool/batch/$rmt.ihave /usr/spool/batch/$rmt.$$
		(
		echo /usr/lib/news/inews -t \"cmsg ihave $DOIHAVE\" \
			-n to.$rmt.ctl '<<END_IHAVES'
		cat /usr/spool/batch/$rmt.$$
		echo END_IHAVES
		) | at now + 3 days 2>/dev/null
		rm -f /usr/spool/batch/$rmt.$$
	else

This queues up an "at" job to run three days hence.  Unfortunately this doesn't
work as-is on BSD systems: I don't know what the BSD equivalent of
"at now + 3 days" is. I stuff the article-ids into the batch job for lack of a
better place to put them.  The result is that the article I posted on bigtex
now has at least three days to get to remote-sys before the ihave gets there:
remote-sys is very unlikely to see the ihave first unless something is wrong
with the news paths, in which case the article *should* be sent via
bigtex!remote-sys.  Assuming that bigtex expires news no quicker than seven
days, the news should still be available if remote-sys sends a sendme.  Of
course, the prospect of a 10K/day mail link zooming to 2meg/day+ when this kicks
in must not be forgotten by anyone allocating dialtone...

If bigtex and remote-sys exchange ihaves in this manner, ihaves are normally
sent but almost never acknowledged with sendmes, because the news arrived
at each system within three days via conventional means.  But if remote-sys's
feed breaks for some reason, the articles that were lost will be automatically
sent by bigtex for the duration of the outage.  Once the feed to remote-sys is
fixed,  remote-sys stops issuing sendmes, and both systems automatically
revert back to normal feed paths.

I had not had a chance to thoroughly test this yet, but hope to soon.  I would
be interested in hearing from anyone doing this now.
-- 
James R. Van Artsdalen    ...!uunet!utastro!bigtex!james     "Live Free or Die"
Home: 512-346-2444 Work: 328-0282; 110 Wild Basin Rd. Ste #230, Austin TX 78746