redis - ZSCAN 保证在迭代过程中得分发生变化的元素

Question

我在文档中找不到此信息:Does Redis guarantee that an element is returned with ZSCAN command under this condition:

The element was contained in the sorted set from the start to the end of a full iteration, BUT the score of such element has changed (even several times, for instance by another client) during iteration?

我找到的唯一相关声明如下:

Elements that were not constantly present in the collection during a full iteration, may be returned or not: it is undefined.

但我不知道在这种情况下分数变化是否与删除/添加操作相同。

Answer 1

如果元素在整个迭代过程中存在，它将通过 zscan 命令返回。在迭代过程中分数是否发生变化无关紧要。

通常，zset 被实现为一个哈希表(即 Redis 的 dict)和一个 skiplist。运行 zscan 命令时，它会遍历哈希表条目以执行扫描作业。分数(字典条目的值)的变化不会影响迭代过程。

如果 zset 足够小，Redis 会将其实现为 ziplist。在这种情况下，Redis 在单个 zscan 调用中返回所有元素。因此在迭代期间不能更改分数。

一句话，你有保障。