RabbitMQ installation (windows) example tutorial

Management background

rabbitmq comes with its own management background, which needs to be configured and turned on after installation
Enter the sbin directory in the rabbitmq installation directory and execute
rabbitmq-plugins enable rabbitmq_management
Restart rabbitmq The service takes effect
Open http://localhost:15672/ to see the management background
The username and password are guest

Configuration instructions

Use the command line to view the queue list

sbin>rabbitmqctl list_queues  
sbin>rabbitmqctl list_queues name messages_ready messages_unacknowledged

Use the command line to view the exchange list

sbin>rabbitmqctl list_exchanges

Define the queue

RabbitMQ does not allow you to redefine an existing one with different parameters queue.

RabbitMQ doesn't allow you to redefine an existing queue with different parameters and will return an error to any program that tries to do that

Reliability

To ensure that messages are not lost, message persistence needs to be set, and the queue must also be durable.
But this is still not 100% reliable, because if RabbitMQ crashes after receiving the message but before completing persistence, the message will be lost.

Repeated processing

Consider the following scenario (premise: queues and messages are durable):

1. The consumer receives a message msgA, half processed, not completed, no ack confirmation was initiated;

2. At this time RabbitMQ crashed;

3. The consumer completed the message msgA Processing;

4. When RabbitMQ restarts, it is found that msgA has not been processed, so msgA is sent to the consumer again.

In this scenario, message msgA will be processed twice, so the consumer side should have a mechanism to prevent repeated processing.

ACK

ACK confirmation only tells RabbitMQ that the consumer has completed processing the message, not that the logical processing is successful. Even if the business processing fails, ACK confirmation is required. . Because generally speaking, if a failure occurs due to business reasons, retrying will not solve the problem. Only failures caused by network interruptions, machine power outages, etc. require retry.

Prevent business load from being concentrated on a certain consumer

channel.basicQos(prefetchCount);

Set
prefetchCount=1
, tell RabbitMQ to only allocate one to one consumer at a time message until the last message assigned to this consumer is acknowledged and processed. In this way, messages will be allocated to idle consumers every time based on actual processing conditions.

About the default Exchange

The default Exchange is implicitly bound to each queue, and the routing key is the queue name. It cannot be explicitly bound or unbound. And it cannot be deleted.

The default exchange is implicitly bound to every queue, with a routing key equal to the queue name. It is not possible to explicitly bind to, or unbind from the default exchange. It also cannot be deleted .

The basic process of messaging

The publisher publishes a message
-->exchange receives the message (if the publisher does not specify a specific Exchange, the default Exchange is used) , and according to the type of exchange and certain routing rules, the message is routed to each queue that meets the routing rules (if there is no matching queue, the message is discarded)
-->The queue sends the message to the subscriber A certain consumer of the queue (if there is no consumer, the message remains in the queue until a consumer consumes the message)

Topic Exchange wildcard character

The asterisk matches a word (note, Not a letter)

* (star) can substitute for exactly one word.
pound sign matches any number of words
# ( hash) can substitute for zero or more words.

The role of the mandatory and immediate flags in the AMQP protocol

Mandatory and immediate are the two flags in the basic.pulish method in the AMQP protocol Bits, they all have the function of returning messages to the producer when the destination cannot be reached during message delivery. The specific difference is:

1. Mandatory flag bit

When the mandatory flag bit is set to true, if the exchange cannot find a qualified queue based on its own type and message routeKey, then basic will be called The .return method returns the message to the producer; when mandatory is set to false, the broker will directly throw away the message in the above situation.

2. immediate flag bit

When the immediate flag bit is set to true, if exchange finds that there is no consumer on the corresponding queue when routing the message to queue(s), then this The message is not put into the queue. When all queues (one or more) associated with the message routeKey have no consumers, the message will be returned to the producer through the basic.return method.

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