@Override
        public String toString() {
            return metrics.entrySet().stream()
                    .map(e -> String.format("%50s: %s", e.getKey(), e.getValue()))
                    .collect(joining("\n"));
        }
A collection of metrics about the currently built {@link PredicateIndex}.
predicate-search/src/main/java/com/yahoo/search/predicate/PredicateIndexBuilder.java