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 <[email protected]> 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: [email protected]
[mailto:[email protected]] 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: [email protected]
[mailto:[email protected]] On Behalf Of
Neelesh Deo Dani
Sent: 02 August 2011 07:42
To: [email protected]
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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