12. A computer program product having a non-transitory computer-readable storage medium storing computer-executable code, the code comprising: a feature manager module of an online system configured to: maintain a cumulative feature store storing feature values determined from user actions performed before a time point; maintain an incremental feature store storing feature values, the maintaining comprising updating feature values of the incremental feature store responsive to receiving information describing user actions performed after the time point; a request processor module configured to: receive a request for a feature value, the request identifying a user and a feature associated with user actions of a type; receive a first partial result from the cumulative feature store, the first partial result determined from user actions of the type performed by the user before the time point; receive a second partial result from the incremental feature store, the second partial result determined from user actions of the type performed by the user after the time point; determine a weighted combination comprising the first partial result and the second partial result, wherein the first partial result is weighted by a decay factor; and return the weighted combination as the requested feature value.
12. A computer program product having a non-transitory computer-readable storage medium storing computer-executable code, the code comprising: a feature manager module of an online system configured to: maintain a cumulative feature store storing feature values determined from user actions performed before a time point; maintain an incremental feature store storing feature values, the maintaining comprising updating feature values of the incremental feature store responsive to receiving information describing user actions performed after the time point; a request processor module configured to: receive a request for a feature value, the request identifying a user and a feature associated with user actions of a type; receive a first partial result from the cumulative feature store, the first partial result determined from user actions of the type performed by the user before the time point; receive a second partial result from the incremental feature store, the second partial result determined from user actions of the type performed by the user after the time point; determine a weighted combination comprising the first partial result and the second partial result, wherein the first partial result is weighted by a decay factor; and return the weighted combination as the requested feature value. 19. The computer program product of claim 12 , wherein the feature manager is further configured to: mark the incremental feature store as inactive and stopping the updates to the feature values stored in the incremental feature store; determine a weighted combination of feature values from the incremental feature store and corresponding feature values from the cumulative feature store, wherein the feature values from the cumulative feature store are weighted by a decay factor; and update the feature values of the cumulative feature store with the weighted combinations.