What Is DMS for RocketMQ?

Distributed Message Service (DMS) for RocketMQ is message-oriented middleware that delivers low latency, high flexibility, high throughput, dynamic expansion, easy management, and abundant messaging functions.

DMS for RocketMQ has the following features:

Compatibility with open-source RocketMQ clients.
Abundant messaging functions, including ordered message delivery, delayed messages, scheduled messages, message retry, dead letter messages, and transactional messages, which meet diverse needs in e-commerce and finance scenarios.
Monitoring and analysis functions, including message tracing, message tracking, trace analysis, dead letter message export, monitoring and alarms, which allow you to monitor your services and keep them up and running.

Product Architecture

Figure 1 Product architecture
Click to enlarge

Architecture description:

Brokers receive and store messages sent by producers or forward messages to consumers. A broker consists of one master and two slave nodes.
NameServers receive and store broker metadata.
Producers obtain metadata from NameServers and send messages to brokers.
Consumers obtain metadata from NameServers and then pull messages from brokers.

Message Types

DMS for RocketMQ supports four messages types.

Normal messages: Messages that do no have any features of delayed messages, ordered messages, or transactional messages.
Delayed/Scheduled messages: Messages that are delivered to consumers after a specific period after being sent from producers to DMS for RocketMQ.
Ordered messages: Messages that are retrieved in the exact order that they are created.
Transactional message: Messages that achieve eventual consistency, delivering distributed transaction processing similar to X/Open XA.

Advanced Features

DMS for RocketMQ provides four advanced features.

Message filtering: Consumers can tag messages in the subscribed topics to retrieve only the required messages.

Message retry: DMS for RocketMQ retries sending messages that fail to be retrieved. If the message retrieval still fails after the maximum number of retries is reached, the messages are sent to the dead letter queue.

Table 1 describes the retry mechanism in DMS for RocketMQ.

**Table 1** Message retry mechanism
Retrieval Type	Retry Interval	Maximum Retries
Ordered retrieval	The interval is set by the suspendTimeMillis parameter. The default interval is 1000 ms, that is, 1s.	The maximum number of retries is set by the setMaxReconsumeTimes method on the consumer. If this parameter is not set, there will be unlimited retries.
Normal retrieval	The interval varies by the retry number, as shown in Table 2.	Set during consumer group creation. Value range: 1–16 times

**Table 2** Intervals between retries in normal retrievals
Retry No.	Interval	Retry No.	Interval
1	10s	9	7 min
2	30s	10	8 min
3	1 min	11	9 min
4	2 min	12	10 min
5	3 min	13	20 min
6	4 min	14	30 min
7	5 min	15	1 h
8	6 min	16	2 h

Delayed messages: After being sent from producers to DMS for RocketMQ, messages are delivered to consumers only after a fixed period. A producer can specify one of the 18 delay levels listed in Table 3.

**Table 3** Delay levels
Delay Level	Delay	Delay Level	Delay
1	1s	10	6 min
2	5s	11	7 min
3	10s	12	8 min
4	30s	13	9 min
5	1 min	14	10 min
6	2 min	15	20 min
7	3 min	16	30 min
8	4 min	17	1 h
9	5 min	18	2 h

Scheduled messages: After being sent from producers to DMS for RocketMQ, messages are delivered to consumers only after a specified time point. In DMS for RocketMQ, you can schedule messages to be delivered at any time within one year. You can also cancel scheduled messages.

This function is supported only for instances created on or after March 30, 2022.