当订户以QOS = 2脱机时，由mosquitto代理发布的消息存储 [英] published message store by mosquitto broker when subscriber is offline with QOS=2

问题描述

我的发布者和订阅者都以QOS = 2的身份连接到mosquitto(paho)代理，并通过clean_session = false维护持久会话.当我与连接到代理的订户发布消息时，订户成功接收到该消息，现在，如果我断开订户的连接，然后再次发布消息并与订户建立连接，那么当我的订户处于脱机状态时，我将能够检索到那些消息.

My both publisher and subscriber are both connected to mosquitto (paho) broker with QOS=2 and maintaining persistent session by clean_session=false. When i publish message with subscriber connected to broker, it successfully received by subscriber, now if I disconnect the subscriber , then again publish message and connect subscriber after, I will be able to retrieve message those messages when my subscriber was offline.

我的问题是-

1. 代理中是否有任何存储，可以在订户脱机时存储所有消息.

1. Is there any storage in the broker which stores all the messages when subscriber is offline.

如果是，则可以存储多长时间或多条消息.

If yes, how much long or how many message it can store.

这种方法是否适合实时GPS跟踪，使订户可以长时间(约5-6小时)下线.

Is this approach is good for real time GPS tracking where subscriber can go offline for a long time (5-6 hr) approx.

即使断电也可以保持会话持久性.

Is session persistence is maintained even if power goes off.

如果我在实时gps跟踪中使用此方法，它可以为可伸缩应用程序处理多少流量.

How much traffic it can handle for scalable application if I use this approach in real time gps tracking..

推荐答案

1. 是的，有一个文件(mosquitto.db).您可以在 mosquitto.conf 文件和persistence*选项

只要存在持久性会话且消息的限制为磁盘空间(对于32位mosquitto，可能为2-4gb)，消息就被存储.但是，无论哪种方式，都会产生大量消息(除非您收到的消息非常笨拙)

Messages are stored as long as there are persistence sessions and the limit is disk space (or possibly 2-4gb for 32bit mosquitto). But either way that is a LOT of messages (unless you have stupidly large messages)

这取决于您的留言率和发布者/订阅者的数量

It depends on you message rates and the number of publishers/subscribers

是的，会话持久性被保存在同一个db文件中，因此在mosquit重启后保持状态

Yes session persistence is kept in the same db file so state is maintained over mosquitto restarts

这实际上取决于您拥有多少个发布者/订户以及邮件率是什么.

Again this really depends on how many publishers/subscribers you have and what the message rates are.

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