ActiveMQ from version 5.4 has an optional persistent scheduler built into the ActiveMQ message broker. It is enabled by setting the broker schedulerSupport attribute to true in the xml configuration. An ActiveMQ client can take advantage of a delayed
mq不支持任意的时间京都,如果要支持,不可避免的需要在Broker层做消息排序,加上持久化方面的考量,将不可避免地带来巨大的性能消耗,所以rocketMQ只支持特定级别的延迟消息. 在Broker短通过messageDelayLevel配置.实现类:org.apache.rocketmq.store.schedule.ScheduleMessageService public class ScheduleMessageService extends ConfigManager { private
Message Delivery Semantics At most once -- Messages may be lost but are never redelivered(消息可能丢失但不会重复投递) At least once -- Messages are never lost but may be redelivered(消息不会丢失但可能重复投递) Exactly once -- this is what people actually want, each message is