I attended the session TS-8434: Ajax Push (a.k.a. Comet) with Java Business Integration (JBI) this afternoon. Here's a report...

The room was very packed and there was a long line of people (including me) waiting in the 'standby line' to get in. Overall the talk was pretty good. I thought the speaker did a good job laying things out and explaining them. The "Demo" he did was *very* difficult to see on the screen, and a bit hard to follow. I was drawn to the session by the abstract ("This session shows how to push your critical business information out to Ajax clients and the browser--with lower latency and without compromising scalability or system performance.").

If you're not familiar with Ajax Push (Comet), there's a very good article, Why Ajax Comet?, that you might want to check out.

Here are some of my notes from the session:

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* What is Ajax Push Good For?

• Use it to create highly responsive, event-driven applications in a browser
• Pros: compared to (standard) Ajax -- lower latency (not dependent on polling frequency)
• Example apps: Gmail and Google Talk, KnowNow, JotLive, etc

* How does "Push" to a Browser work? (pushing data to a browser)

• Deliver data over a previously opened connection... always "keep a connection open" (back channel)

* Architectural Challenges

• Using blocking, synchronous techn will result in a blocked thread for each open connection that is "waiting"
• will consume memory
• lowers scalability and can effect perf
• to get the JVM to scale up to 10K threads+ needs specific tuning and is not an efficient way to do this

* Technology Solutions - use NIO non-blocking sockets to avoid blocking a thread per connection, use technologies that support asynchronous request processing.

* How does JBI fit into the picture?

• the JBI 1.0 (JSR 208) framework provides the basis for building loosely coupled composite apps by combining services
• JBI is inherently async, which complements the async nature of Ajax Push

* Potential drawbacks and pitfalls

• beware of flooding clients with too many events (don't go overboard pushing out events too rapidly)
• firewalls may terminate connections after a certain amount of time
• solution: re-establish connection after tear-down or at certain intervals
• Re: security -- very similar to standard Ajax apps

* Summary

• pushing data to the web client can form a crucial tool in the dev arsenal when latency is impt
• "long poll" is straight forward and portable
• "streaming" today is more complex and has portability implications
• JBI complements the async nature of Ajax push