@Override
    public String toString() {
        return "EffectiveMetaSet{" +
               "feed='" + feed + '\'' +
               ", type='" + type + '\'' +
               ", set=\n" + effectiveStreamsToString(effectiveMetas) +
               '}';
    }
@return An unmodifiable set of {@link EffectiveMeta} in ascending order
of {@link EffectiveMeta#getEffectiveMs()}
stroom-meta/stroom-meta-api/src/main/java/stroom/meta/api/EffectiveMetaSet.java