Basic Concepts of RocketMQ¶

This page lists some basic concepts of RocketMQ to help you better understand and use RocketMQ.

Topic¶

A topic is a top-level container that is used in RocketMQ to transfer and store messages that belong to the same business logic.

MessageType¶

Categories defined by message transfer characteristics for type management and security verification. RocketMQ support NORMAL, FIFO, TRANSACTION and DELAY message type.

MessageQueue¶

MessageQueue is a container that is used to store and transmit messages in RocketMQ. MessageQueue is the smallest unit of storage for RocketMQ messages.

Message¶

A message is the smallest unit of data transmission in RocketMQ. A producer encapsulates the load and extended attributes of business data into messages and sends the messages to an RocketMQ broker. Then, the broker delivers the messages to the consumer based on the relevant semantics.

MessageView¶

MessageView is read-only interface to message from a development perspective. The message view allows you to read multiple properties and payload information inside a message, but you cannot make any changes to the message itself.

MessageTag¶

MessageTag is a fine-grained message classification property that allows message to be subdivided below the topic level. Consumers implement message filtering by subscribing to specific tags.

MessageOffset¶

Messages are stored in the queue in order of precedence, each message has a unique coordinate of type Long in the queue, which is defined as the message site.

ConsumerOffset¶

A message is not removed from the queue immediately after it has been consumed by a consumer, RocketMQ will record the last consumed message based on each consumer group.

MessageKey¶

MessageKey is The message-oriented index property. By setting the message index, you can quickly find the corresponding message content.

Producer¶

A producer in RocketMQ is a functional messaging entity that creates messages and sends them to the server. A producer is typically integrated on the business system and serves to encapsulate data as messages in RocketMQ and send the messages to the server.

TransactionChecker¶

RocketMQ uses a transaction messaging mechanism that requires a producer to implement a transaction checker to ensure eventual consistency of transactions.

TransactionResolution¶

A status identifier of a transaction during the sending of a transactional message in RocketMQ. The broker controls whether a transactional message should be committed and delivered based on the transaction status. Transaction states include transaction commit, transaction rollback, and transaction pending.

ConsumerGroup¶

A consumer group is a load balancing group that contains consumers that use the same consumption behaviors in RocketMQ.

Consumer¶

A consumer is an entity that receives and processes messages in RocketMQ. Consumers are usually integrated in business systems. They obtain messages from RocketMQ brokers and convert the messages into information that can be perceived and processed by business logic.

ConsumeResult¶

The result returned by a PushConsumer message listener in RocketMQ after it finishes processing a message, used to indicate whether the message was processed correctly. The consumption result includes consumption success and consumption failure.

Subscription¶

A subscription is the rule and status settings for consumers to obtain and process messages in RocketMQ. Subscriptions are dynamically registered by consumer groups with brokers. Messages are then matched and consumed based on the filter rules defined by subscriptions.

Message Filtering¶

Consumers can filter messages by subscribing to specified message tags (Tag), ensuring that only the filtered message set is ultimately received. The calculation and matching of filter rules are completed on the RocketMQ broker.

Reset Consumer Offset¶

Using the timeline as the coordinate, reset the consumption progress of a consumer group on a subscribed topic within the time range of message persistence. After the setting is complete, the consumer will receive the messages that the producer sends to the RocketMQ broker after the specified point in time.

Message Trace¶

The complete link information aggregated from data such as the time and place of each related node during the process from a message being sent by the producer to being received and processed by the consumer. With message traces, you can clearly locate the complete path of a message from the producer, through the RocketMQ broker, to the consumer, which facilitates troubleshooting.

Message Accumulation¶

The producer has already sent messages to the RocketMQ broker, but because the consuming capacity of the consumer is limited, it cannot correctly consume all messages within a short period of time. At this point, unconsumed messages are stored on the broker. This state is called message accumulation.

Transactional Messages¶

Transactional messages are an advanced message type provided by RocketMQ, supporting eventual consistency between message production and local transactions in distributed scenarios.

Scheduled/Delayed Messages¶

Scheduled/delayed messages are an advanced message type provided by RocketMQ. After a message is sent to the broker, it can only be consumed by the consumer after a specified time. By setting a certain scheduled time, a delayed scheduling trigger effect in distributed scenarios can be achieved.

Ordered Messages¶

Ordered messages are an advanced message type provided by RocketMQ, supporting consumers to obtain messages in the order in which they were sent, thereby achieving sequential processing in business scenarios.

For more information, see the Apache RocketMQ official documentation.

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