private long roundTimeToInterval(final long timestampMillis, final long intervalMillis) {
        return (timestampMillis / intervalMillis) * intervalMillis;
    }
@return the short code name of the row key interval, e.g 's'
stroom-legacy/stroom-legacy-model_6_1/src/main/java/stroom/legacy/model_6_1/EventStoreTimeIntervalEnum.java