[rules-users] running multiple instance of rule engine

Tue Aug 2 06:41:27 EDT 2011

Why don't you do it in a single session?

The overhead created by the procedure you describe is considerable.

And you may run into synchronisation problems such as that the first event
has gone to host A, the second one goes to host B, but A hasn't stored the
event yet...

-W

2011/8/2 Neelesh Deo Dani <neeleshdev at 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 at 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 at lists.jboss.org [mailto:
> rules-users-bounces at 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 at lists.jboss.org [mailto:
> rules-users-bounces at lists.jboss.org] *On Behalf Of *Neelesh Deo Dani
> *Sent:* 02 August 2011 07:42
> *To:* rules-users at 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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