blocks|key|1172551|text|在我看来，这个想法可能更类似于“进程优先级”，而不是优先级队列中的优先级值。当然，这与JMS规范中关于它的一两句话是一致的，显然也与AMQP规范一致。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1172552|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It seems to me that the idea is probably more akin to "process priority" than the priority values in a priority queue. Certainly that is consistent with the sentence-or-two about it in the JMS spec, and evidently with the AMQP spec as well.

blocks|key|1172636|text|人们必须小心，因为太多的优先级没有用到使用程序变得比浏览每条消息更繁重的程度。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1172637|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

One has to be careful in that too many priorities aren't used to the point where using the program becomes more burdensome than going through each message.

blocks|key|958230|text|顺便说一句，ActiveMQ现在通过JMSPriority标头支持5.4.x中的priority+messaging。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|958231|通常有更好的技术来实现优先级消耗，而不是让message+broker在消息到达时对某些缓冲区中的消息进行重新排序，例如having+a+dedicated+consumer+pool+for+high+priority+messages。那么，不管来自低优先级消息的噪声有多大，高优先级消息总是会被通过。|958232|考虑到消息传递的异步特性，如果使用JMSPriority报头等，则很容易用低优先级消息填充缓冲区、网络管道和prefetch+queues。|958233|entityMap|0|LINK|mutability|MUTABLE|url|http://activemq.apache.org/|1|https://issues.apache.org/jira/browse/AMQ-2789|2|http://activemq.apache.org/how-can-i-support-priority-queues.html|3|http://activemq.apache.org/what-is-the-prefetch-limit-for.html^0|6|8|0|14|I|1|0|1O|1N|2|0|1I|F|3|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]|$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|F|3|G|5|6|7|16|8|@]|9|@$A|17|B|18|1|19]]|C|$]]|$1|H|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]|R|$5|K|L|M|C|$N|S]]|T|$5|K|L|M|C|$N|U]]]]

BTW <a href="http://activemq.apache.org/">ActiveMQ</a> now supports <a href="https://issues.apache.org/jira/browse/AMQ-2789">priority messaging</a> in 5.4.x via JMSPriority headers.

Rather than getting the message broker to re-order messages within some buffer as they arrive, there are often better techniques to implement priority consumption, such as <a href="http://activemq.apache.org/how-can-i-support-priority-queues.html">having a dedicated consumer pool for high priority messages</a>. Then irrespective of how much noise there is from low priority messages, high priority messages will always get though. 

Given the asynchronous nature of messaging its easy to fill up buffers, network pipes and <a href="http://activemq.apache.org/what-is-the-prefetch-limit-for.html">prefetch queues</a> with low priority messages if using things like JMSPriority headers etc.

blocks|key|958282|text|消息传递系统针对时间顺序进行了设计和优化。文件系统针对附加文件而不是在开头或中间插入数据进行了优化。类似队列的数据结构通常针对追加到末尾和从头删除进行了优化。对于文件系统，这意味着附加到文件(添加)和附加到事务日志(删除)，以及一旦消息文件被使用(删除)就删除它们。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|958283|将优先级引入处理队列可以有效地将队列转换为同时具有按时间和优先级排序的数据结构。基本上，当涉及到使用文件存储时，它是相当不理想的，因为您必须创建某种索引策略。|958284|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Messaging systems are designed and optimized for chronological ordering. File systems are optimized for appending files and not inserting data at the beginning or in the middle. Queue-like data structures are usually optimized for append at the end and removal from the head. For file systems, this means appending to file (adding) and appending to a transaction log (removal), and deleting message files once they are consumed (removal).

Introducing priorities to a processing queue effectively turns the queue into a data structure that has both chronological and priority sorting. Basically, when it comes to working with file storage, it's quite sub-optimal as you have to create some sort of indexing strategy.

It seems like most of the messaging systems I've looked at have basic, if any, support for priority message queues. For example, the AMQP only <a href="http://www.amqp.org/confluence/download/attachments/720900/amqp.0-10.xml?version=1" rel="noreferrer">specifies</a> a minimum of 2 priorities. RabbitMQ, an AMQP implementation, <a href="http://www.trapexit.org/forum/viewtopic.php?p=48220" rel="noreferrer">doesn't support</a> any priorities. ActiveMQ will be <a href="https://issues.apache.org/activemq/browse/AMQ-2789" rel="noreferrer">getting support</a> for 10 message priorities in version 5.4 in a couple days. 10 priority levels is the specified by the <a href="http://shafi.adderpit.com/jdk/j2eedocs/api/javax/jms/Message.html#getJMSPriority%28%29" rel="noreferrer">JMS spec</a>.

A <a href="http://en.wikipedia.org/wiki/Priority_queue" rel="noreferrer">priority queue</a> in the non-messaging sense of the word orders its contents based on an arbitrary field with an unconstrained range of priorities. Why does an implementation like this not exist as part of a messaging system? As I asked in the title, is priority an inherently non-messaging concept?

I realize that one answer might be that the concept of priority introduces the possibility of messages infinitely languishing in the queue while higher priority messages are processed. Are there other reasons?

Is message priority inherently unimportant in message queue systems?

消息队列

文件存储

数据结构

文件系统

我看过的大多数消息传递系统似乎都有对优先级消息队列的基本支持。例如，AMQP仅至少2个优先级。RabbitMQ，一个AMQP的实现，任何优先级。在5.4版本中，ActiveMQ将在几天内为10个消息优先级提供。10优先级是由指定的。非消息意义上的基于任意字段对其内容进行排序，该字段具有不受限制的优先级范围。为什么这样的...

问消息优先级在消息队列系统中本质上是不重要的吗？
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问消息优先级在消息队列系统中本质上是不重要的吗？
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