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From Gianny Damour <>
Subject Re: Effectiveness of WADI's Design and Implementation Comforted
Date Thu, 18 Oct 2007 22:17:59 GMT
On 17/10/2007, at 11:53 PM, Jeff Genender wrote:

> Gianny Damour wrote:
>> Excerpt of the conclusion:
>> "
>> The effectiveness of the design and implementation of WADI's  
>> distributed
>> session lookup engine and replication engine is further comforted  
>> by the
>> observed average response times and scalability characteristics.
>> For the considered scenarios, WADI performs better than Terracotta,
>> which is not really surprising as...
> If I may comment here...Without fine-grained clustering  
> capabilities, I
> have a hard time believing that WADI can outperform Terracotta.
> Especially with large objects...WADI would push over the entire object
> each time, where Terracotta would only ship the changed members.   
> If you
> are going to publish the numbers you did, you probably should explain
> what is getting pushed across.


I believe you simply skimmed through what I have been writing:  
firstly, I did provide a description of the state stored in session.  
Secondly, your comment about large objects and the inadequacy of  
WADI's design to handle them is clearly and explicitly discussed in  
the  second paragraph of the conclusion. As redundancy of information  
is not much of a problem for theoretical clustering discussions, I am  
reiterating: WADI does provide a fine grained replication mechanism,  
which is able to track field updates or method executions and replay  
them against replicas. If you are interested by this kind of stuff,  
then please feel free to have a look to this WIKI page - http://

At this stage, the delta replication stuff is under performing and  
resource intensive: to give you an idea, its average response time is  
6.10ms for the third test scenario (average response time for default  
replication mechanism is 4.77ms for WADI and 6.36ms for Terracotta).  
Once again, as a preliminary comment to Ari's response, this is a  
scenario with HTTP session stickiness on. After this week-end, the  
performance for fine-grained replication should improve  
significantly. I intend to: get ride of native reflection; index  
constructor, field and methods description for really fast packaging  
on wire and resolution when reading back from a byte stream; and re- 
use reflective invokers (CGLIB FastMethod/Constructor and ASM  
customed field updaters).

FWIW, I do not see support of large objects as crucial as you for Web  
solutions. Even if I spent a couple of months working on wadi-aop to  
provide this feature, it was more with the ultimate goal to leverage  
it for efficient distributed caching than HTTP session replication. I  
truly believe that large scale Web solutions requiring HA have to be  
designed with this constraint in mind; with this constraint in mind,  
keeping session size small sounds reasonable.

>> "
>> If people are interested by clustering development, then please  
>> respond
>> as I will resume some Geronimo clustering work and could really  
>> use a hand.
> I am in the midst of getting OpenEJB clusterable.  I would be happy to
> combine forces and get clustering finished up for G ;-)

Great! Will post back to the dev@ list as soon as I resume Geronimo  
clustering work.


>> Thanks,
>> Gianny

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