Posted by jhurley
on May 10, 2007 at 9:21 PM PDT
Notes from an informative session on Ajax Comet and JBI...
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
If you're not familiar with Ajax Push (Comet), there's a very good article,
Comet?, that you might want to check out.
Here are some of my notes from the session:
* 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
- 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