Quick Note on Sessions

Allo all,
  Berny is quite right about the scalability troubles surrounding
HttpSessions, or session of anykind.  Here is the basic problem "The user is
slow, the machine is fast and memory realistate is expensive."   This
analogy works like this:
  A user has a large object in memory on the session, the user takes for
ever (10seconds--10000ms) to do something with it.  Ok this does not seem
bad, now add 10,000 users/minute and you have a 5minute timeout on the
session.... say a 50kB object in memory... 5*10kB*50k= 2.5GB of memory.(only
500MB of memory if you account for rolloff)  In addition when one scales
this in a clustered environment the session state must be mirrored to each
cluster node so each node adds linearly to the session memory...  so with 10
machines handling 1000users/minute each we wind up with the 2.5GB peak
memory and 500MB avg memory on each machine in the 10 node cluster.

There are several activities working on a solution to this problem.  A solid
one is JCache which is a distributable/clusterable Caching mechanism.   Also
look at the whitepapers of your HttpEngine to find out how it handles the
session state problem.  In the mean time JCache is what I use.

Good luck all,


Paul S. Kossler
Sr.Software Engineer
CACI Chesapeake

 <<Kossler, Paul S..vcf>>