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From ikarzali <>
Subject Re: Effectiveness of WADI's Design and Implementation Comforted
Date Thu, 18 Oct 2007 07:02:20 GMT

jgenender 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.

Interesting test of Terracotta.  I wouldn't trust any test that pegs the CPU
at 100%.  May I suggest the following potential changes:

1. Running Jetty, Grinder, and Terracotta on a single laptop should change. 
Run Terracotta on its own server.  It will run faster even though it won't
be over loopback.

2. Run sticky and see what happens.  See, the test is not testing the same
thing with WADI and Terracotta.  With WADI, the clustering implementation is
configured to keep data on  a finite number of nodes.  With Terracotta, you
have a consistent clustered view of sessions.  Since you are round-robin,
with Terracotta every node is holding a reference to every session and as
the sessions change, all Jetty nodes are updated with the change.  So, round
robin WITH WADI replication off is actually pretty much cheating because TC
has the sessions in all nodes and WADI has them in one.  Run sticky sessions
in your load balancer.  Then Terracotta will have the session in one node
just like WADI.  _Then_ you will have apples-to-apples and maybe find TC
latency to be lower and throughput higher.

I would be happy to help explain more but this use of WADI and Terracotta
seem like you are getting opposite behaviors out of the products (full n-way
replication with no SPoF under Terracotta versus zero replication under
WADI) and a different test will more accurately reflect the relative
performance of the systems.


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