[rules-users] Performance of collect seems to be n-squared

I have a simple class Post { int id; ... }. I insert some number of them as facts and then call ksession.execute(facts); The whole drl file (except for package and import statements) is: rule "collect" when $a : ArrayList(size > 0) from collect(Post()); then System.out.println("Number of posts: " + $a.size()); System.out.println("DONE"); end The time it takes to run is n-squared in the number of posts. For 4000, 8000, 16000, 32000, 64000 posts the time is (in 1/10 seconds): 4, 14, 56, 220, 852 Is this expected? Is there a better way for me to do the collect?