[Standards-JIG] pubsub: cache-last-item

Bob Wyman bob at wyman.us
Sat Feb 18 23:00:42 UTC 2006

Peter Saint-Andre wrote:
> Right now the text in version 1.8pre7 has "SHOULD cache" but 
> for the generic JEP-0060 cases this probably needs to be MAY
	I would strongly support changing this to a "MAY" in the base
JEP-0060 specification.
	Having said that let me point out that PubSub.com actually caches
the last 128 messages for each of the well over a million JEP-0060
subscriptions that we service. Those who pull RSS or Atom files from our
site are really just getting dumps of their JEP-0060 message caches... 

> (with the proviso that non-generic profiles of pubsub, such as
> PEP, can define other requirements regarding this feature).
	We should always permit application specific profiles to impose more
stringent requirements on client and server developers. Converting a "MAY"
to a "SHOULD" or "MUST" is precisely what profiles are all about. However, I
would strongly encourage developers to be very careful about making such a
requirement. Is it *really* necessary to make things work or is it merely a
convenience? For instance, JEP-0060 provides a very complete mechanism with
which one can reach into a cache and pull out old messages. One should only
make it a requirement to automatically deliver the last cached message in
those situations where it is certain that this is, in fact, always the right
thing to do and that it is sufficient. For instance, if it is often
necessary to pull more than one message from the cache, then requiring this
"one message" cache simply confuses matters. (i.e. you get one message
delivered automatically but the others you will need to pull out on your own
while being careful not to pull the same message twice...)

	bob wyman

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