[rules-users] Trapping runaway rules

[Wolfgang Laun]

On 30 August 2011 14:27, Dean Whisnant <dean at basys.com> wrote:

> My project involves rule creation by customers, business analysts, and
> developers.  We have a base set of rules that fire for every transaction and
> then we fire custom rules within a stateful session.  An issue I've started
> to run into is rules being created that fire endlessly.  I initialize the
> session with an event listener that we use to extract all rules fired for
> each line item of a transaction.  Once the session is initialized and all
> rules from various agenda groups loaded we do a fireall rules.
>
> My questions are:
> 1) how can I detect I have a runaway rule/rules.
>        Is there a method or listener that could detect this for me?  Does
> anyone have a formula they use to do so?  I had thought that I could use my
> event listener that I track the rules with to grab the last X number of
> rules fires and see if rule y gets fired more that z times.  But is there a
> simpler method?
>

It's not even as simple as that. ;-) Multiple firing of a rule r within n
firings may not be loops if this happens with different facts bound to
patterns.



> 2) once I've detected a runaway rule, how can I gracefully stop drools rule
> execution? I read of the command drools.halt in different posts, but not
> sure if this would be what I'm looking at doing.
>

If you detect it during a consequence execution, throw an exception and
catch it with a custom consequence exception handler.

Using a limit on fire all rules might be another way, in combination with
logging all activations.

Finally, someone with a little savvy should be able to detect some just by
looking at them. The telltale marks are well known...

-W


>
> Any thoughts are appreciated.
>
> Thank you!
>
> Dean
>                StatefulKnowledgeSession ksession =
> buildOutgoingStatefulKnowledgeSession(supportingUDTList);
>                // AgendaEventListener agendaListener = new
> HipaaAgendaListener();
>                ksession.addEventListener(_ruleLog);
>
>                for (int i = 0; i < _agendaGroups.size(); i++)
>                {
>                        if (_log.isDebugEnabled()) _log.debug("Focus on
> Agenda Group " + _agendaGroups.get(i));
>
>  ksession.getAgenda().getAgendaGroup(_agendaGroups.get(i)).setFocus();
>                        // Fire them all
>                        try
>                        {
>                                ksession.fireAllRules();
>                        }
>                        catch (Exception e)
>                        {
>                                _log.error("FireAllRules exception. Error="
> + e.getMessage()); // error
>                        }
>                }
>
>
>
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