@Override
    public String toString() {
        final long total = total();
        if (total == 0) {
            return "success% = NaN (0/0)";
        }
        final double percentageOfSuccess = 100 * successRate();
        return String.format("success%% = %.2f%% (%d/%d)", percentageOfSuccess, success(), total);
    }
Returns the failure rate (failure/total), or throws an {@link ArithmeticException} if total is 0.
core/src/main/java/com/linecorp/armeria/common/util/EventCount.java