@Override
    public boolean equals(@Nullable Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof EventCount)) {
            return false;
        }
        final EventCount that = (EventCount) o;
        return success == that.success && failure == that.failure;
    }
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