Re: Scalable publish/subcribe with JavaSpaces ?

Hi,

Before attempting to answer any of these questions - have you considered
the registerForAvailability method on JavaSpace05 in your thinking so far?

http://www.jini.org/files/specs/porter/api/net/jini/space/JavaSpace05.html

Best wishes,

Dan.

Christian wrote:
> Hi,
> I was just asking myself how the notify operation that was added to the
> JavaSpaces API (compared to the original set of operations available in
> the Linda tuple space) positions it to the publish/subscribe paradigm.
> One might think at the first sight that by introducing the notify
> operation into the space API a new communication paradigm is created
> that is more complex and more powerful than simple publish/subscribe.
>
> However, the persistent nature of the shared data space has also a flip
> side.
> The common task that is typical for all publish/subscribe services,
> namely simply the notification of all interested subscribers about an
> event, is very difficult to implemented in a scalable fashion.
> Saving all notifications that occur in the space is usually not possible
> because most application scenarios involve so many notifications that
> the space will run out of memory.
> The normal eviction functionality of tuple spaces cannot be used either
> to remove notifications. If the “time to live” property of a tuple is to
> short it might not get delivered to all interested subscribers, if it is
> too long the space could again run out of memory.
>
> In order to handle huge amounts of notifications in a short time, each
> space would have to know the exact number of active subscribers for a
> notification in order to decide whether a notification can be removed
> safely.
> This number however can change dynamically during the lifetime of a
> notification. Another approach would be to automatically delete a
> “notification tuple” after it has been matched to all templates that
> were active at the time the matching process began.
> This behaviour would need a special treatment of “notification tuples”.
> The support for these “one-shot” tuples is as far as I understand not
> really part of the idea behind shared data spaces (namely using a share
> space to persist data)
>   and would require a special space implementation.
>
> I know that there are publish/subscribe implementations that are based
> on tuple spaces. For example GigaSpaces offers a JMS API.
> I was wondering whether this is only possible by creating a new space
> implementation or whether it can be done with the current JavaSpace API.
>  Note, that I'm talking about huge amounts of notifications that are
> published in a short time frame.
> I think publish/subscribe with small or moderate notifcations rates
> should be realizable with the current JavaSpace implementation.
>
> I really would like to hear your opinions and thoughts about this topic.
>
> Best regards
> Christian
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