2011/8/2 Neelesh Deo Dani <neeleshdev@yahoo.co.in>

Following example clarifies the question:
I've Event declaration and rule as follows:

declare Event
    @role(event)
    @timestamp(datetime)
    datetime : Date
    name : String
end

rule "Contest"
no-loop
when
    $e1 : Event(name == "event1")
    $e2 : Event(name == "event2", this after $e1)
then
    System.out.println("rule Contest fired");
end

If Event with name "event1" is inserted in the session and after that Event with name "event2" is inserted in the same session, then the temporal operator ("this after $e1" ) will work fine. But, if these two events are inserted in two different sessions ( rule engine running on different host), then it won't work. I'm trying to find a solution for this scenario. One way is to persist the events as well in datastore and whenever any event comes, insert all the previous events also in the session (by fetching from datastore). In this example, when event2 comes (to host2), fetch event1 from datastore and insert it in the session so that temporal operator will work.

Is there any better alternative exists for this scenario?

Thanks,
Neel

--- On Tue, 2/8/11, Abhay B. Chaware <Abhay.Chaware@kpitcummins.com> wrote:

What do you expect to happen in the scenario mentioned, assuming you are running only 1 rules session? Whatever you expect to happen in this case ( e.g. latest update wins ), you will need to implement in your persistence logic If you are using separate rule engines/instances.

by the way, have you looked at drools grid ? I haven’t used it, but appears to solve a similar problem that you are trying to – distributed computing.

-abhay

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Swindells, Thomas
Sent: Tuesday, August 02, 2011 1:47 PM
To: Rules Users List
Subject: Re: [rules-users] running multiple instance of rule engine

I’m not sure I understand the question.

You have two totally independent rule engine on two different servers running with separate JVMs and sessions.

You happen to share data between the two sessions by updating a database but drools has no knowledge of that (they are just java objects which happen to exist) and they certainly aren’t the same object on both servers.

Temporal reasoning and correlation of events will therefore only happen on the facts that are inserted into that processes working memory – there’s no way it could be any way else as it only know about itself, there could be 10 or 0 other processes running it won’t know the difference.

The ideal method is to have an application design where each request is totally independent from all other requests (other than db state) and therefore you do exactly as you have described – there is no other state to share. If you have to share state between them you have a much bigger problem and you probably have to find some other way to partition up the data into separate blocks.

Thomas

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Neelesh Deo Dani
Sent: 02 August 2011 07:42
To: rules-users@lists.jboss.org
Subject: [rules-users] running multiple instance of rule engine

Hi,
I need a setup where multiple instance of drools rule engine will be running in different physical hosts. In each host, a web server (API) will be running which will receive an input event, process it and insert into rule engine (session) for rules execution on the same host. I'm using external persistent datastore. The objects will be populated from datastore before inserting into the session. After rule execution if there is any change in the state of the objects the same will be stored back to the datastore. The datastore calls are made outside the rule execution.
In this scenario, if an event comes to one host and another event comes to a different host, how will the temporal reasoning or correlation of events work? What is the recommended way of deploying multiple instance of rule engine for scalability?
Please help in this regard.

Thanks & Regards,
Neel

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