How to implement priority queue based on RabbitMQ

How to implement priority queue based on RabbitMQ
Overview

For various reasons, up to now, RabbitMQ has not implemented a priority queue, but only implemented priority processing for Consumer.

However, for various reasons, Priority Queues are required at the application layer, so the requirement is: how to add priority queue features to RabbitMQ.

After querying the information, I learned that although RabbitMQ does not officially support this feature, the Community already has the relevant priority queue plug-in, and this plug-in is listed on the official website of RabbitMQ.

Address: http://www.rabbitmq.com/community-plugins.html

Plugin installation

Do not download the link in this url immediately. First download the corresponding plug-in from another location based on the version of rabbitmq you want to update. For example:

The plug-in directories of the two major versions will be listed (select the corresponding directory to download, otherwise an error will be reported ...):

 

How to install the plug-in?

Enter the rabbitmq installation directory, enter the plugins directory, copy the ez File above to the plugins directory, and then run the command to enable this plug-in.

In CentOS, the default path is/usr/lib/rabbitmq/lib/rabbitmq_server-3.3.4/plugins (the version number may change)

In windows, the default path is C: \ Program Files \ RabbitMQ Server \ rabbitmq_server-3.3.4 \ plugins (the version may change)

Copy the ez File and run the following command to list the plug-ins:

Find the priority queue plug-in named rabbitmq_priority_queue.

Run: rabbitmq-plugins enable rabbitmq_priority_queue

OK. Restart the rabbitmq-server service.

In this way, the server configuration is complete.

 

C # changes required by the code end

Let's take a look at the compilation of the client Class Library:

First, we need to define priority enumeration to inherit from byte, because the C # client priority of RabbitMQ is transmitted using byte:

First define three levels of priority: low, medium, and high (in fact, many levels can be defined, just to simplify, so only three levels are defined)

There are two changes:

1. Custom Attributes must be added to the queue.
2. Set custom attributes when sending messages to rabbitmq

Internal static IDictionary <string, object> QueueArguments {get {IDictionary <string, object> arguments = new Dictionary <string, object> (); arguments ["x-max-priority"] = 10; // defines the queue priority as 10 levels return arguments ;}}

 

Channel. QueueDeclare ("queueName", true, false, false, QueueArguments); // QueueArguments is the dictionary defined above.

Var headers = channel. createBasicProperties (); headers. priority = (byte) msg. priority; // here, convert the enumeration inherited from byte to bytechannel. basicPublish ("exchange", "route", headers, SerializerUtility. serialize2Bytes (msg ));

Other notes

In the rabbitmq-server instance with the priority queue plug-in installed, all Durable queues must use the above method to set the x-max-priority attribute. Otherwise, the rabbitmq-server Service will crash

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