熔断降级是指当资源处于不稳定的情况下,在接下来的时间窗口之内,对该资源的调用都自动熔断。我们通常用两种方式来衡量资源是否处于稳定的状态:
如RT Degrade demo 所示,一个资源每次需要500 ms。那么观察这个例子的结果,发现每过10 秒,就会恢复对该资源的调用,但是很快这个资源又会被降级(平均响应时间仍然不满足需求)。
注意:为了统计异常比例,必须保证资源用下面的代码包围:
Entry entry = null;
try {
entry = SphU.entry(key, EntryType.IN, key);
// Write your biz code here.
// <<BIZ CODE>>
} catch (Throwable t) {
if (!BlockException.isBlockException(t) {
Tracer.trace(t);
}
} finally {
if (entry != null) {
entry.exit();
}
}
运行Demo,将可以看到:
1529399827825,total:0, pass:0, block:0
1529399828825,total:4263, pass:100, block:4164 // 第一秒的平均RT 都还比较小
1529399829825,total:19179, pass:4, block:19176
1529399830824,total:19806, pass:0, block:19806 // 开始被降级
1529399831825,total:19198, pass:0, block:19198
1529399832824,total:19481, pass:0, block:19481
1529399833826,total:19241, pass:0, block:19241
1529399834826,total:17276, pass:0, block:17276
1529399835826,total:18722, pass:0, block:18722
1529399836826,total:19490, pass:0, block:19492
1529399837828,total:19355, pass:0, block:19355
1529399838827,total:11388, pass:0, block:11388
1529399839829,total:14494, pass:104, block:14390 // 10 秒之后恢复,然而又迅速地
被降级
1529399840854,total:18505, pass:0, block:18505
1529399841854,total:19673, pass:0, block:19676