[rules-users] drools performance with <

[Greg Barton]

This is not at all surprising.  To set up and run the rules there's quite a bit of code running behind the scenes besides just the comparison test. (For instance, there's object creation just to track the fact that two objects matched the rule, and in this case those objects are created for every possible combination of TestObject instances before the first rule ever fires, then added to lists, and so on...  So in the case of 1000 TestObject instances, there's 1,000,000 object creations and list additions just for that.) 

So, as has been said many times on this list, and probably in a few blogs, for any given algorithm a hard coded java version will invariably be faster than rules.  What rules gives you is a way to express solutions to complex problems in a flexible and comprehensible way.  It shines when the problems are so complex that coding them procedurally is pit of the question.

The same relationship is there between C and java.  Java gives you managed, portable code, but for that you give up the raw speed of C.

--- On Thu, 1/21/10, Tom Carchrae <carchrae at gmail.com> wrote:

> From: Tom Carchrae <carchrae at gmail.com>
> Subject: [rules-users] drools performance with <
> To: rules-users at lists.jboss.org
> Date: Thursday, January 21, 2010, 6:40 PM
> Hello,
> 
> I'm new to Drools and am trying it out.  I've found it
> easy enough so
> far, but quickly ran into a performance bottleneck. 
> (perhaps an all
> too familiar story! :) ).  So, I made a simple example
> to try and
> track down the behavior.  Here it is.
> 
> I wanted to create a rule that uses an < comparison
> between pairs of
> objects.  The following are the performance results:
> 
> 10 objects.  Java comparison took 0 ms
> 10 objects.  Rule firing took 2516 ms
> 100 objects.  Java comparison took 0 ms
> 100 objects.  Rule firing took 1984 ms
> 1000 objects.  Java comparison took 47 ms
> 1000 objects.  Rule firing took 132500 ms
> 10000 objects.  Java comparison took 4641 ms
> 10000 objects. Rule firing took .... (please wait...)
> 
> Here is the rule
> 
> rule "A < B"
>     when
>         a : TestObject( 
> )
>         b : TestObject(
> valueDouble < a.valueDouble )
>     then
>        
> b.setValueint(b.getValueint()+1);    
> end
> 
> Now, I do understand that this (worst-case) is a comparison
> of N x N
> objects... so, 1000 = 1000000 comparisons.  However,
> ~100ms per
> comparison seems relatively expensive for such a simple
> check.  I am
> using StatefulKnowledgeSession (I tried Stateless but this
> gave only a
> mild performance improvement - and I would also like to use
> insert in
> some of my rules).
> 
> How would one speed up such a query?  I know part of
> the problem is
> the < comparison.  The results with == are much
> better (presumably, it
> can do lots of pruning of the space)
> 
> Model creation 0
> 10 objects.  Rule firing took 2829 ms
> 100 objects.  Rule firing took 93 ms
> 1000 objects.  Rule firing took 657 ms
> 10000 objects.  Rule firing took 3375 ms
> 100000 objects.  Rule firing took 33266 ms
> 
> I have thought about clever tricks that I could do to try
> and speed
> things up, like sorting into groups, etc.  But it all
> seems relatively
> convoluted.  Am I correct in coming to the conclusion
> that a <
> comparison is not the kind of thing that you should do in
> Drools?
> 
> How would you go about this?  I would prefer to keep
> all the logic in
> the DRL files.  I'm guessing you do a Java based
> comparison and use a
> fire-once rule to invoke this code.
> 
> Thanks in advance for any insight,
> 
> Tom
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