DateTime currentStartDate = startDate.plusDays(i * numDaysPerCohort);
DateTime currentEndDate = startDate.plusDays((i + 1) * numDaysPerCohort);
List<Integer> userIdsList = Lists.newArrayList();
Set<Integer> userIdsSet = Sets.newHashSet();
EventIndex.Callback aggregateUserIdsCallback = new AggregateUserIds(eventStorage, userStorage,
new DummyIdList(), eventFilter, TrueFilter.INSTANCE, userIdsList, userIdsSet);
shardedEventIndex.enumerateEventIds(
groupByEventType,
currentStartDate.toString(DATE_TIME_FORMATTER),
currentEndDate.toString(DATE_TIME_FORMATTER),
aggregateUserIdsCallback);