Using Drools in a heavy batch process

Question

We used Drools as part of a solution to act as a sort of filter in a very intense processing application, maybe running up to 100 rules on 500,000 + working memory objects. turns out that it is extremely slow. anybody else have any experience using Drools in a batch type processing application?

Answer 1

I haven't worked with the latest version of Drools (last time I used it was about a year ago), but back then our high-load benchmarks proved it to be utterly slow. A huge disappointment after having based much of our architecture on it.

At least something good I remember about drools is that their dev team was available on IRC and very helpful, you might give them a try, they're the experts after all: irc.codehaus.org #drools

Answer 2

Drools is not really designed to be run on a huge number of objects. It's optimized for running complex rules on a few objects.

The working memory initialization for each additional object is too slow and the caching strategies are designed to work per working memory object.

Answer 3

We were looking at drools as well, but for us the number of objects is low so this isn't an issue. I do remember reading that there are alternate versions of the same algorithm that take memory usage more into account, and are optimized for speed while still being based on the same algorithm. Not sure if any of them have made it into a real usable library though.

Answer 4

Kind of depends on your rules - 500K objects is reasonable given enough memory (it has to populate a RETE network in memory, so memory usage is a multiple of 500K objects - ie space for objects + space for network structure, indexes etc) - its possible you are paging to disk which would be really slow.

Of course, if you have rules that match combinations of the same type of fact, that can cause an explosion of combinations to try, which even if you have 1 rule will be really really slow. If you had any more information on the analysis you are doing that would probably help with possible solutions.

Answer 5

I'm just learning drools myself, so maybe I'm missing something, but why is the whole batch of five hundred thousand objects added to working memory at once? The only reason I can think of is that there are rules that kick in only when two or more items in the batch are related.

If that isn't the case, then perhaps you could use a stateless session and assert one object at a time. I assume rules will run 500k times faster in that case.

Even if it is the case, do all your rules need access to all 500k objects? Could you speed things up by applying per-item rules one at a time, and then in a second phase of processing apply batch level rules using a different rulebase and working memory? This would not change the volume of data, but the RETE network would be smaller because the simple rules would have been removed.

An alternative approach would be to try and identify the related groups of objects and assert the objects in groups during the second phase, further reducing the volume of data in working memory as well as splitting up the RETE network.

Answer 6

Use a stateless session and add the objects one at a time ?

Answer 7

I've used a Drools with a stateful working memory containing over 1M facts. With some tuning of both your rules and the underlying JVM, performance can be quite good after a few minutes for initial start-up. Let me know if you want more details.

Answer 8

shabbydoo please give me some details on tuning drools on linux with 32bit platform thanks