This topic introduces terms that are used in ApsaraMQ for RocketMQ to help you better understand and use ApsaraMQ for RocketMQ.
topic
A top-level container that is used to transmit and store messages that have the same consumption logic in ApsaraMQ for RocketMQ. Topics are identified and distinguished by topic name. For more information, see Topics.
message type
To facilitate message management and security verification, messages in ApsaraMQ for RocketMQ are classified into different types based on transmission characteristics. ApsaraMQ for RocketMQ supports the following types of messages: normal messages, ordered messages, transactional messages, scheduled messages, and delayed messages.
message queue
The actual container that is used to store and transmit messages in ApsaraMQ for RocketMQ. Queues are the smallest storage units for messages. A topic in ApsaraMQ for RocketMQ consists of multiple queues based on which horizontal partitioning and streaming storage are performed. Queues are identified and distinguished by queue ID. For more information, see Message queues.
message
The smallest unit of data transmission in ApsaraMQ for RocketMQ. Producers encapsulate the loads and extended attributes of business data into messages and send the messages to ApsaraMQ for RocketMQ brokers. Then, the brokers deliver the messages to consumers based on the corresponding semantics. For more information, see Messages.
message view
A read-only operation that ApsaraMQ for RocketMQ provides for developers. Developers can use message views to read information about multiple attributes and loads in messages. Message views cannot be used to modify information in messages.
message tag
A fine-grained classification attribute provided by ApsaraMQ for RocketMQ. You can use message tags to label messages in a topic. Consumers can filter messages by subscribing to specific message tags. For more information, see Message filtering.
message offset
In ApsaraMQ for RocketMQ, messages are queued in a topic in the order that they arrive at the topic. Each message is assigned a unique long-type coordinate. This coordinate is known as the offset of the message. For more information, see Consumer progress management.
consumer offset
After a consumer consumes a message, the message is not immediately deleted from the queue. ApsaraMQ for RocketMQ records the offset of the latest consumed message in each consumer group. This offset is called consumer offset. For more information, see Consumer progress management.
message key
An index attribute provided by ApsaraMQ for RocketMQ to manage messages. You can set a message key to quickly find the message content to which the message key corresponds.
producer
A functional entity that creates and sends messages to brokers in ApsaraMQ for RocketMQ. Integrated into business systems, producers encapsulate data into messages and send the messages to ApsaraMQ for RocketMQ brokers. For more information, see Producers.
transaction checker
A listener used by producers in ApsaraMQ for RocketMQ to perform local transaction checks and abnormal transaction recovery. A transaction checker checks and determines the status of transactional messages based on the status of business data. For more information, see Transactional messages.
transaction resolution
An identifier of the transaction status of transactional messages in ApsaraMQ for RocketMQ. Brokers use transaction resolutions to determine whether to commit and deliver transactional messages. Transaction resolutions include commit, rollback, and pending. For more information, see Transactional messages.
consumer group
A load balancing group that contains consumers that have the same consumption behaviors in ApsaraMQ for RocketMQ. Consumer groups are not functional entities but logical resources. ApsaraMQ for RocketMQ initializes multiple consumers in a consumer group to achieve the scaling of consumption performance and high availability disaster recovery. For more information, see Consumer groups.
consumer
A functional entity that receives and processes messages in ApsaraMQ for RocketMQ. Integrated into business systems, consumers obtain messages from ApsaraMQ for RocketMQ brokers and convert the messages into processable information for processing by consumption logic. For more information, see Consumers.
consumption result
The result returned by the listener of a push consumer in ApsaraMQ for RocketMQ after a message is consumed. A consumption result is used to identify whether a message is correctly consumed. A consumption result can be successful or failed.
subscription
The rule and status settings for consumers to obtain and process messages in ApsaraMQ for RocketMQ. Subscriptions are dynamically registered by consumer groups with brokers. Messages are matched and consumed based on filtering rules defined by subscriptions. For more information, see Subscriptions.
message filtering
Consumers can filter messages by subscribing to specific tags to receive only the type of messages that the consumers want. Filtering rules are calculated and matched on ApsaraMQ for RocketMQ brokers. For more information, see Message filtering.
consumer offset resetting
To reset a consumer offset, you can use the timeline as the coordinate and reset the consumer progress of the topics to which the consumer group subscribes within the time range of persistent storage. After the setting is complete, consumers can receive messages that are sent to the ApsaraMQ for RocketMQ broker after the specified time. For more information, see Consumer offset.
message trace
The complete route record of a message from the publication by a producer to the consumption by a consumer. A message trace consists of the time, location, and other information on each node. A message trace records the routing information about a message that is sent from a producer to an ApsaraMQ for RocketMQ broker, and then to a consumer. Message traces can help you troubleshoot issues.
message accumulation
If consumers are not allocated sufficient resources to consume all messages in a short period of time, the messages are stacked and stored on the ApsaraMQ for RocketMQ broker. This phenomenon is called message accumulation.
transactional message
A type of featured message provided by ApsaraMQ for RocketMQ to ensure the ultimate consistency between message production and local transaction.
scheduled or delayed message
A type of featured message provided by ApsaraMQ for RocketMQ. Scheduled or delayed messages allow consumers to consume messages that are sent to brokers after a specific period of time or at a specific point in time. You can use scheduled or delayed messages to implement delayed scheduling and triggering in distributed scenarios.
ordered message
A type of featured message provided by ApsaraMQ for RocketMQ. Ordered messages are delivered to consumers in the order in which the messages are sent. This type of message allows you to implement ordered processing in business scenarios.