[rules-users] Snapshot of drools engine's state

[Wolfgang Laun]

On 12/08/2013, IK81 <ml at kofler.me> wrote:
> Thanks for your reply. The way you described this is actually how my
> proof-of-concept works. However, I implemented it using two timestamps.
> First I use the @timestamp annotation for the property of the event. This
> property is set by the event source. Second, I persist a second timestamp
> that reflects the timestamp of the session's pseudo clock when I inserted
> the event. From my naive feeling I need both for a reproducible replay
> starting with the last snapshot of the session.

The (original) @timestamp property is the one used by the Engine,
right? Then the real or pseudo time of insertion is irrelevant
(except, perhaps, for logging, but then you don't need to save it in
the event).

Another issue. What is the recovery meant to cure? Application and/or
Drools bugs? In this case: what if the faithful recovery runs into the
same bug? If it is a HW glitch, redundancy might be the way to go. For
powerfail, there's UPS...

If not losing a single beat is essential you are most likely not on
the right track with a system that can't claim to be free of errors,
for any "community release". (Support only solves problems only after
they become manifest.) OTOH, if you can, it might be better to think
about a way to start again with a minimum of disturbance. It depends
on the app domain, of course...

-W

>
> Thanks for the hint concerning the sliding window. This is the drawback of
> the approach of externally controlling the clock - it limits the time
> granularity of these not-event-B-after-A rules. But in my case I can live
> with this restriction that the rule might fire some seconds later. I wished
> there would exist a possibility to register for a kind of callback when to
> externally trigger the event engine again - however, I haven't found
> anything related to that.
>
> Thanks & best regards,
> Ingo
>
>
>
> --
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