What is a topic in SMQ? - Simple Message Queue (formerly MNS)

This topic provides an overview of topics in Simple Message Queue (SMQ, formerly MNS), covering their definition, relationship with other components, properties, and limits.

Definition and relationship with other components

In SMQ, a topic is a container that stores messages. The messages of a topic can be subscribed to and consumed in multiple channels. Message subscribers can be queues, HTTP servers, Short Message Service (SMS), Direct Mail, and Mobile Push.

Each subscriber can subscribe to all messages of a topic. You can also configure rules to filter messages by tag.

Features

At-least-once delivery: Each message, within its retention period and maximum delivery attempts, is received and processed by a receiver at least once.
Multiple subscriber types: The messages of a topic can be delivered to the following types of subscribers: queues, HTTP servers, SMS, Direct Mail, and Mobile Push.
Message filtering: Subscribers can use tags to filter messages and subscribe only to the messages that match specified filtering rules.

Topic properties

Topic name

Description: the name of the topic, which is the globally unique identifier of the topic in a cluster.
Value: The name must be up to 120 characters in length and can contain letters, digits, and hyphens (-). It must start with a letter.

Maximum message size

Description: the maximum size of the message body that can be sent to the topic. Unit: KB.
Valid values: 1 to 64. Default value: 64.

Whether to enable logging

Description: specifies whether to enable the logging feature for the topic. If the logging feature is enabled, SMQ automatically pushes the operation logs of the topic to the specified logging bucket. You can then view the message trace, delay, and other information from the logs. For more information, see Log management.
Valid values: true and false.

Limits

Item	Limit	Description
Name length	120 characters	If this limit is exceeded, the topic fails to be created.
Number of topics	1,000 Note If you require more topics, you can log on to Quota Center console and submit an application to increase the Maximum Topic Quantity in a Single Region. For more information, see Submit an application to increase a quota.	None.
Message size	64 KB	If this limit is exceeded, the message is discarded.
Number of subscriptions to a single topic	100	None.
Message retention period	One day	We recommend that you specify a message retention period based on your business requirements. After the specified period expires, the message is deleted.
Message filtering tag	1	A message filtering tag can be up to 16 characters in length.
Topic subscription on queues	The size of an SMQ queue is equal to or larger than the size of an SMQ topic.	If the limit is exceeded, the subscription fails to be created.