[rules-users] Best approach for handling parallel requests for a stateful rules session

[jkrupka]

We've been over multiple ways of handling multiple parallel requests for a
stateful rules session and I want to make sure the approach we have settled
on makes sense.

We will be getting multiple requests at a time to run some score calculation
rules for various products.  In the past we used stateless rules sessions to
do this and it worked fine.  In the newer version of our application we are
using significantly more data to do our calculation and are pretty sure
stateful is the way to go.  That being said, can we use the same session in
multiple threads?  Based on our understanding, a session isn't inherently
thread safe, so we are thinking we will need to do one of two things:

1. Synchronize all updates to facts and the calling of fireAllRules so that
only one thread is doing this at a time.  Is this the best (or only safe)
approach in this situation?  Since all fact updates and rules running in
done in one thread, when is throughput a concern (obviously depends on
hardware, # of rules, # of facts, etc)?
2. Ensure that only one thread updates the facts related to a given product
at a time.  Multiple threads could still call fireAllRules at the same time,
but after the rules finish, the calling class would grab the facts that
would have been updated for just the product that it's interested in.  That
way, it doesn't matter if the rules were technically matched in a different
thread, as long as I'm grabbing just the data I'm interested in.   Is this a
safe approach?  Does it end up offering more throughput capability than
approach #1?

Josh

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