@Override
        public String toString() {
            return "AggregateState{" +
                   "createTime=" + createTime +
                   ", aggregateDir=" + aggregateDir +
                   ", partCount=" + partCount +
                   ", itemCount=" + itemCount +
                   ", totalBytes=" + totalBytes +
                   '}';
        }
@return Current age of the aggregate, i.e. time between its creation time and now
stroom-proxy/stroom-proxy-app/src/main/java/stroom/proxy/app/handler/PreAggregator.java