什么是幂等运算?
当前回答
无论调用该操作多少次,结果都是相同的。
其他回答
对于工作流管理器(如Apache workflow),如果管道中的幂等操作失败,系统可以自动重试该任务而不影响系统。即使日志发生了变化,这也很好,因为您可以看到事件。
在这种情况下,最重要的是您的系统可以重试失败的任务,并且不会弄乱管道(例如,每次重试都在表中添加相同的数据)
任何操作,每n个结果都会产生与第1个结果值匹配的输出。例如,-1的绝对值是1。-1的绝对值的绝对值是1。-1绝对值的绝对值的绝对值等于1。等等。请参见:什么时候使用递归是非常愚蠢的?
简而言之,幂等运算意味着无论你做多少次幂等运算都不会得到不同的结果。
例如,根据HTTP规范的定义,GET、HEAD、PUT、DELETE是幂等操作;但是POST和PATCH不是。这就是为什么有时POST被PUT取代的原因。
对集合的幂等运算在应用一次或多次时,其成员保持不变。
它可以是像absolute(x)这样的一元运算,其中x属于一组正整数。这里absolute(absolute(x)) = x。
它可以是一个二进制操作,比如集合与自身的并集总是返回相同的集合。
干杯
my 5c: In integration and networking the idempotency is very important. Several examples from real-life: Imagine, we deliver data to the target system. Data delivered by a sequence of messages. 1. What would happen if the sequence is mixed in channel? (As network packages always do :) ). If the target system is idempotent, the result will not be different. If the target system depends of the right order in the sequence, we have to implement resequencer on the target site, which would restore the right order. 2. What would happen if there are the message duplicates? If the channel of target system does not acknowledge timely, the source system (or channel itself) usually sends another copy of the message. As a result we can have duplicate message on the target system side. If the target system is idempotent, it takes care of it and result will not be different. If the target system is not idempotent, we have to implement deduplicator on the target system side of the channel.