@Override
    public double getExceptionRate() {
        long invokeCount = getInvokeCount();
        return invokeCount == 0 ? -1 : CalculateUtils.divide(getExceptionCount(), invokeCount);
    }
Gets useless cycle.

@return the useless cycle
fault/fault-tolerance/src/main/java/com/alipay/sofa/rpc/client/aft/impl/AbstractInvocationStat.java