[rules-users] Query for a fact, and concurrent rule execution

Wed May 2 10:49:16 EDT 2012

I would suggest making your service stateless and run the service in 
multiple JVMs to alleviate performance concerns. You will be able to scale 
and also not have to worry about cramming everything into a 
StatefulKnowledgeSession and worry abt thead-safety.

From:   Stephen Lomax <stephen.lomax at mattelli.com>
To:     Rules Users List <rules-users at lists.jboss.org>, 
Date:   05/02/2012 04:28 AM
Subject:        Re: [rules-users] Query for a fact, and concurrent rule 
execution
Sent by:        rules-users-bounces at lists.jboss.org

Hi Mike,

Many thanks for that..we had previously thought of serialising to file but 
thought the purpose of the StatefulKnowledgeSession was to keep it live in 
memory continuously, rather than instantiating a new session with each web 
service call.

My concern is that if we instantiate a new session with each web service 
call the memory required will increase massively (if we have many 
concurrent requests).  Is there a way of serving multiple concurrent 
requests against the same session to remove that concern.

Many thanks for your help with this..it is very much appreciated.

Ste

.
On 2 May 2012, at 12:08, Michael Anstis wrote:

That's a possibility, but it'd depend on your rules.

As a thought, you could serialise the initialised 
StatelessKnowledgeSession into a byte[] (cached at application scope) and 
deserialise with each web-service call.

I would wait to see if Mark Proctor, Edson Tirelli or community members 
have other thoughts on use of a single StatefulKnowledgeSession.

IIRC it is meant to be thread-safe but think people have reported problems 
in the past. Recently: 
http://lists.jboss.org/pipermail/rules-dev/2012-February/003857.html

With kind regards,

Mike

On 2 May 2012 11:58, Stephen Lomax <stephen.lomax at mattelli.com> wrote:
Hi Mike,

Each quote does not enrich the session, we were actively looking to remove 
the quote at the end of the session to prevent it growing as we were just 
comparing the quote to the core product attribute facts.

What is the performance hit in launching a Stateful knowledge session with 
say 10,000 facts, would it make the web service call slow?

Thanks very much for the help on the query also…we will look into that.

Kind Regards

Ste

On 2 May 2012, at 11:31, Michael Anstis wrote:

Does each quote validation exercise enrich the StatefulKnowledgeSession 
with other facts that could influence validation of other quotes?

If not probably using a StatefulKnowledgeSession per HTTP request might be 
more simple (with the KnowledgeBase as an application scoped variable).

Regarding retrieval of results, there are a couple of options that spring 
to mind:-
Look at using a Global to collate results.
Look at using a Query (
http://stackoverflow.com/questions/5872215/how-do-i-add-facts-to-working-memory-at-runtime-in-the-drools-drl-and-retrieve-t
)
With kind regards,

Mike

On 2 May 2012 10:39, stelomax <stephen.lomax at mattelli.com> wrote:
Hi,

Please bear with me, I am relatively new to the world of Drools and have a
question.  I am hoping it will be a simple issue.

First let me frame my planned implementation at a high level.  I am hoping
to use Drools as a real time service enabled quote validation tool.

Facts representing products and attributes will be loaded into a stateful
knowledge session upon boot (using a piece of Java that loads these as 
facts
from our product DB).

The front-end application will allow users to build up quotes consisting 
of
quote lines that make references to these products.  Once the quote is 
built
they will press a "Validate" button.  This will call a webservice that 
will:

1) Insert the quote details as facts into the knowledge session
2) Run a "rule flow" to validate the quote against the product facts
3) The rules will insert validation results as facts tagged against the
quote
4) QUERY for the validation results
5) Retract the facts for the quote (inc validation results)
6) Send the validation results back as a response to the webservice call

My first question is how to implement step 4 --> how to physically query 
for
the validation results pertaining to that specific quote.  Any help here
would be greatly appreciated.

My second question relates to concurrency.  As this is a quote validation
tool there will be multiple users validating quotes so we will get
concurrent validation requests.

What is the recommended manner of dealing with concurrent rule requests
within a stateful knowledge session.  If 2 people attempt to validate a
different quote at the same time we will have two quotes within the
knowledge session together with all of the product facts.  Is drools 
capable
of running two concurrent rule flows against the knowledge session, each
referencing a different quote or would we need to instantiate 2 knowledge
sessions, or even deal with the matter in a serial manner placing the 2nd
quote validation flow on hold until the first completes?

Any help/pointers would be great.  I am hoping someone out there has
attempted to use Drools in a similar manner :)

Many Thanks

Ste

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