10. The computer-implemented method of claim 1 , wherein the online system further maintains feature loops, each feature loop aggregating values of a feature expression across a plurality of actions.
10. The computer-implemented method of claim 1 , wherein the online system further maintains feature loops, each feature loop aggregating values of a feature expression across a plurality of actions. 15. The computer-implemented method of claim 10 , wherein a feature loop is evaluated periodically at a fixed time interval.