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.68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Introduction</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">What is RocketMQ</span><meta itemprop="position" content="2"></li></ul></nav><span class="theme-doc-version-badge badge badge--secondary">Version: 4.x</span><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><h1>What is RocketMQ</h1><p>People subscribe to some of their favorites by applications. |
| When an author publishes an article to the relevant section, we can receive relevant news feeds.</p><p>Pub/Sub is a messaging paradigm where message senders(called publishers, producers) send messages directly to specific recipients (called subscribers, consumers). The basic message model of RocketMQ is a simple Pub/Sub model.</p><div class="theme-admonition theme-admonition-tip alert alert--success admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 12 16"><path fill-rule="evenodd" d="M6.5 0C3.48 0 1 2.19 1 5c0 .92.55 2.25 1 3 1.34 2.25 1.78 2.78 2 4v1h5v-1c.22-1.22.66-1.75 2-4 .45-.75 1-2.08 1-3 0-2.81-2.48-5-5.5-5zm3.64 7.48c-.25.44-.47.8-.67 1.11-.86 1.41-1.25 2.06-1.45 3.23-.02.05-.02.11-.02.17H5c0-.06 0-.13-.02-.17-.2-1.17-.59-1.83-1.45-3.23-.2-.31-.42-.67-.67-1.11C2.44 6.78 2 5.65 2 5c0-2.2 2.02-4 4.5-4 1.22 0 2.36.42 3.22 1.19C10.55 2.94 11 3.94 11 5c0 .66-.44 1.78-.86 2.48zM4 14h5c-.23 1.14-1.3 2-2.5 2s-2.27-.86-2.5-2z"></path></svg></span>Concepts</div><div class="admonitionContent_S0QG"><div class="tabs-container tabList__CuJ"><ul role="tablist" aria-orientation="horizontal" class="tabs"><li role="tab" tabindex="0" aria-selected="true" class="tabs__item tabItem_LNqP tabs__item--active">Producer</li><li role="tab" tabindex="-1" aria-selected="false" class="tabs__item tabItem_LNqP">Consumer</li><li role="tab" tabindex="-1" aria-selected="false" class="tabs__item tabItem_LNqP">Topic</li></ul><div class="margin-top--md"><div role="tabpanel" class="tabItem_Ymn6">The producer is responsible for producing messages, and the business system is generally responsible for producing messages. A producer sends messages generated in the business application system to the broker server.RocketMQ provides a variety of sending methods, synchronous sending, asynchronous sending, sequential sending, and one-way sending.<p>learn more ➡️ <a href="/docs/4.x/producer/01concept1">Producer</a></p> </div><div role="tabpanel" class="tabItem_Ymn6" hidden="">Aims to consume messages, which are generally responsible by the backend system (asynchronous consumption). A message consumer pulls messages from the Broker server and serves them to the application. From the perspective of user applications, two consumption methods are provided: pull consumption and push consumption.<p>learn more ➡️ <a href="/docs/4.x/consumer/01concept2">Consumer</a></p> </div><div role="tabpanel" class="tabItem_Ymn6" hidden="">RocketMQ's fundamental unit of event organization is called Topic. Each Topic contains several messages, and each message can only belong to one topic.<p>learn more ➡️ <a href="/docs/4.x/producer/01concept1">basic concept</a></p> </div></div></div></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="rocketmqs-message-model-a-simple-pubsub-model">RocketMQ's message model, a simple Pub/Sub model<a href="#rocketmqs-message-model-a-simple-pubsub-model" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><p><img loading="lazy" alt="RocketMQ model" src="/assets/images/RocketMQ概念模型-db2c246ff6aa79016f880e2ca7a447e7.png" width="1487" height="277" class="img_ev3q"></p><div class="theme-admonition theme-admonition-note alert alert--secondary admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 14 16"><path fill-rule="evenodd" d="M6.3 5.69a.942.942 0 0 1-.28-.7c0-.28.09-.52.28-.7.19-.18.42-.28.7-.28.28 0 .52.09.7.28.18.19.28.42.28.7 0 .28-.09.52-.28.7a1 1 0 0 1-.7.3c-.28 0-.52-.11-.7-.3zM8 7.99c-.02-.25-.11-.48-.31-.69-.2-.19-.42-.3-.69-.31H6c-.27.02-.48.13-.69.31-.2.2-.3.44-.31.69h1v3c.02.27.11.5.31.69.2.2.42.31.69.31h1c.27 0 .48-.11.69-.31.2-.19.3-.42.31-.69H8V7.98v.01zM7 2.3c-3.14 0-5.7 2.54-5.7 5.68 0 3.14 2.56 5.7 5.7 5.7s5.7-2.55 5.7-5.7c0-3.15-2.56-5.69-5.7-5.69v.01zM7 .98c3.86 0 7 3.14 7 7s-3.14 7-7 7-7-3.12-7-7 3.14-7 7-7z"></path></svg></span>Basic Messaging System Model</div><div class="admonitionContent_S0QG"><p> The figure above exemplifies message model, including a <strong>Producer</strong>, a <strong>Topic</strong>, and a <strong>Consumer</strong>.</p></div></div><p>In a <strong>topic-based</strong> system, messages are published on topics or channels. Consumers will receive all messages on the topics they subscribe to, and producers are responsible for defining the message categories that subscribers subscribe to. This is a basic conceptual model, and in practical applications, the structure will be more complex. For example, in order to support high concurrency and horizontal scaling, the topics need to be partitioned. The same topic will have multiple producers, the same information will have multiple consumers, and load balancing should be performed between consumers.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="rocketmq-extended-message-model">RocketMQ extended message model<a href="#rocketmq-extended-message-model" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><p><img loading="lazy" alt="RocketMQ basic model" src="/assets/images/RocketMQ基本模型-ebcf3458d04b36f47f4c9633c1e36bf7.png" width="1387" height="695" class="img_ev3q"></p><div class="theme-admonition theme-admonition-note alert alert--secondary admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 14 16"><path fill-rule="evenodd" d="M6.3 5.69a.942.942 0 0 1-.28-.7c0-.28.09-.52.28-.7.19-.18.42-.28.7-.28.28 0 .52.09.7.28.18.19.28.42.28.7 0 .28-.09.52-.28.7a1 1 0 0 1-.7.3c-.28 0-.52-.11-.7-.3zM8 7.99c-.02-.25-.11-.48-.31-.69-.2-.19-.42-.3-.69-.31H6c-.27.02-.48.13-.69.31-.2.2-.3.44-.31.69h1v3c.02.27.11.5.31.69.2.2.42.31.69.31h1c.27 0 .48-.11.69-.31.2-.19.3-.42.31-.69H8V7.98v.01zM7 2.3c-3.14 0-5.7 2.54-5.7 5.68 0 3.14 2.56 5.7 5.7 5.7s5.7-2.55 5.7-5.7c0-3.15-2.56-5.69-5.7-5.69v.01zM7 .98c3.86 0 7 3.14 7 7s-3.14 7-7 7-7-3.12-7-7 3.14-7 7-7z"></path></svg></span>Extended message model</div><div class="admonitionContent_S0QG"><p>The above picture is an extended message model, including <strong>two producers</strong>, <strong>two topics</strong>, and <strong>two sets of consumers Comsumer</strong>.</p><p>The <strong>Broker</strong> that stores message topics is the proxy server for the actual deployment process.</p></div></div><ul><li><p>for<strong>Horizontal scaling</strong>, RocketMQ partitions Topic through <strong>MessageQueue</strong></p></li><li><p>for<strong>Concurrent consumption</strong>, the concept of Consumer Group came into being.</p></li></ul><div class="theme-admonition theme-admonition-info alert alert--info admonition_LlT9"><div class="admonitionHeading_tbUL"><span class="admonitionIcon_kALy"><svg viewBox="0 0 14 16"><path fill-rule="evenodd" d="M7 2.3c3.14 0 5.7 2.56 5.7 5.7s-2.56 5.7-5.7 5.7A5.71 5.71 0 0 1 1.3 8c0-3.14 2.56-5.7 5.7-5.7zM7 1C3.14 1 0 4.14 0 8s3.14 7 7 7 7-3.14 7-7-3.14-7-7-7zm1 3H6v5h2V4zm0 6H6v2h2v-2z"></path></svg></span>info</div><div class="admonitionContent_S0QG"><ul><li>Consumer mainly has two consumption modes, namely <strong>broadcast mode</strong> and <strong>cluster mode</strong> (the most commonly used cluster mode is shown in the figure).</li><li>Consumer instances in the same Consumer Group are load balancing consumption. As shown in the figure, ConsumerGroupA subscribes to TopicA and TopicA corresponds to 3 queues. Then Consumer1 in GroupA consumes messages from MessageQueue 0 and MessageQueue 1, and Consumer2 consumes messages from MessageQueue2.</li></ul></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="rocketmq-architecture">RocketMQ Architecture<a href="#rocketmq-architecture" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><p>How do Producer and Consumer find the addresses of Topic and Broker? How are messages sent and received?</p><p><img loading="lazy" alt="RocketMQ Architecture" src="/assets/images/RocketMQ部署架构-ee0435f80da5faecf47bca69b1c831cb.png" width="1342" height="541" class="img_ev3q"></p><p>The main Apache RocketMQ components are Producers, Consumers, NameServers, and Brokers:</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="producer"><strong>Producer</strong><a href="#producer" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>A producer serves as a data source that optimizes, writes, and publishes messages to one or more topics. Producers load balance data among brokers through MessageQueue. It supports fail-fast and retries during sending messages.</p><p>Producers can send messages in either synchronous or asynchronous mode. In synchronous mode, the producer waits for an acknowledgment from the broker before proceeding, while in asynchronous mode, the producer sends the message and continues with its operation without waiting for an acknowledgment.</p><p>Producers can also specify a key for each message they send. The key is used by the broker to determine which partition within a topic the message should be stored in.</p><p>Producers can also specify a callback function that will be invoked once the broker acknowledges receipt of the message. This allows the producer to handle any errors that may occur during message transmission.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="consumer"><strong>Consumer</strong><a href="#consumer" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>Consumers read data by reading messages from the topics to which they subscribe.</p><ul><li>Supports message consumption in two modes: push and pull.</li><li>Supports <strong>cluster mode</strong> and broadcast mode consumption</li><li>Provide real-time message subscription mechanism</li></ul><h2 class="anchor anchorWithStickyNavbar_LWe7" id="nameserver"><strong>NameServer</strong><a href="#nameserver" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><p>NameServer is a simple Topic routing registry that supports dynamic registration and discovery of Topic and Broker.</p><p>Mainly includes two functions：</p><ul><li><strong>Broker management</strong>:The NameServer accepts the registration information of the Broker cluster and saves it as the basic data of the routing information. And it provides a heartbeat detection mechanism to check whether the Broker is still alive.</li><li><strong>Routing Information Management</strong>:Each NameServer will hold the entire routing information about the Broker cluster and queue information for client queries. The Producer and Consumer can know the routing information of the entire Broker cluster through the NameServer, so as to produce and consume messages.</li></ul><p>NameServer usually has multiple instances deployed, and each instance does not communicate with each other. Broker registers its own routing information with each NameServer, so each NameServer instance saves a complete routing information. The client can still obtain routing information from other NameServers, When a NameServer goes offline for some reason.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="broker">Broker<a href="#broker" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><p>Broker is mainly responsible for message storage, delivery and query, as well as service high availability guarantee.</p><p>NameServer is stateless, so it can be deployed in clusters without any information synchronization between nodes. Compared with nameserver, broker is more complicated.</p><p>In the Master-Slave architecture, the Broker is divided into Master and Slave. |
| ，regularly obtains Topic routing information from NameServer, establishes long connections to Master and Slave that provide Topic services, and send heartbeats to Master and Slave regularly. Consumer subscribes to topic from Master or Slave.</li></ul></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="rocketmq-workflow">RocketMQ Workflow<a href="#rocketmq-workflow" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="1-start-the-rocketmq-nameserver">1. Start the RocketMQ NameServer<a href="#1-start-the-rocketmq-nameserver" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>The NameServer listens to the port and waits for the connection of the Broker, Producer, and Consumer after startup.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="2-start-the-rocketmq-broker">2. Start the RocketMQ Broker<a href="#2-start-the-rocketmq-broker" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>The Broker maintains long connections with all NameServers, gets current Broker information, and stores all Topic information after startup. After successful registration, a mapping relationship will be built between Topic and Broker in the NameServer cluster.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="3-create-a-topic">3. Create a topic<a href="#3-create-a-topic" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>The Broker should be specified before creating a Topic, or automatically create one while sending messages.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="4-write-messages-to-the-topic">4. Write messages to the topic<a href="#4-write-messages-to-the-topic" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>The Producer starts by establishing a long-term connection with one device of the NameServer clusters, obtains the Broker information where the current topic exists from the NameServer, polls to select a queue from the queue list, and establishes a long-term connection where the queue is located. This enables the Producer to send messages to the Broker.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="5-read-messages-from-the-topic">5. Read messages from the topic<a href="#5-read-messages-from-the-topic" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>The Consumer establishes a long-term connection with one of the NameServers, obtains which brokers the current subscription topic exists on, and then directly establishes a connection channel with the Broker, and then starts to consume messages.</p></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/apache/rocketmq-site/tree/new-official-website/docs/01-introduction/03whatis.md" target="_blank" rel="noreferrer noopener" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col lastUpdated_vwxv"></div></div></footer></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><a class="pagination-nav__link pagination-nav__link--prev" href="/docs/4.x/introduction/02quickstart"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Quickstart</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/docs/4.x/producer/01concept1"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">Core Concept</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#rocketmqs-message-model-a-simple-pubsub-model" class="table-of-contents__link toc-highlight">RocketMQ's message model, a simple Pub/Sub model</a></li><li><a href="#rocketmq-extended-message-model" class="table-of-contents__link toc-highlight">RocketMQ extended message model</a></li><li><a href="#rocketmq-architecture" class="table-of-contents__link toc-highlight">RocketMQ Architecture</a><ul><li><a href="#producer" class="table-of-contents__link toc-highlight"><strong>Producer</strong></a></li><li><a href="#consumer" class="table-of-contents__link toc-highlight"><strong>Consumer</strong></a></li></ul></li><li><a href="#nameserver" class="table-of-contents__link toc-highlight"><strong>NameServer</strong></a></li><li><a href="#broker" class="table-of-contents__link toc-highlight">Broker</a></li><li><a href="#rocketmq-workflow" class="table-of-contents__link toc-highlight">RocketMQ Workflow</a><ul><li><a href="#1-start-the-rocketmq-nameserver" class="table-of-contents__link toc-highlight">1. Start the RocketMQ NameServer</a></li><li><a href="#2-start-the-rocketmq-broker" class="table-of-contents__link toc-highlight">2. Start the RocketMQ Broker</a></li><li><a href="#3-create-a-topic" class="table-of-contents__link toc-highlight">3. Create a topic</a></li><li><a href="#4-write-messages-to-the-topic" class="table-of-contents__link toc-highlight">4. Write messages to the topic</a></li><li><a href="#5-read-messages-from-the-topic" class="table-of-contents__link toc-highlight">5. 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