[rules-users] Garbage collection and sliding windows (Drools 5.5.0 Final)

[Wolfgang Laun]

The original post mentioned "performance tests with Drools Fusion" in
combination with using the feature of automatic event retraction. I
don't think that OutOfMemory problems in this kind of scenario are due
to some bug in Drools (Fusion) - at least not until I see a complete
test app that reproduces the claimed problem.

It's important to note that automatic event retraction incurs a
considerable overhead in addition to the work required for getting the
event fact off the Rete
network. Essentially, a "Job" (i.e., the retraction) is scheduled for
punctual execution using a TimerService. One must therefore take care
that the system can cope with the additional work of disbanding all of
this contraband - otherwise it'll just clog, and croak.

Running fireUntilHalt() in one thread while inserting events from
another one and expecting automatic event retraction to happen after
10s (due to a window:time(10s)) is one way of risking that the system
runs into overload. With time slices being allotted equably to
threads, a backlog will accumulate if the expire/retract takes longer
than the insert/start-timer.

I've run the aforementioned scenario with System.sleep(nms) after
every so many insertions, and this keeps the system in balance.
Reducing nms gradually will - eventually - stress the system beyond
its breaking point, and OutOfMemory occurs. (To fill up memory more
quickly, the Event class was stuffed with some "dead data" -
char[2000].)

-W