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class="theme-doc-markdown markdown"><h1>FAQs</h1><p>Common questions about the RocketMQ project:</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="1-basic">1 Basic<a href="#1-basic" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><ol><li><p><strong>Why should we use RocketMQ instead of choosing other products?</strong></p><p>Please refer to<a href="http://rocketmq.apache.org/docs/motivation/" target="_blank" rel="noopener noreferrer"> why choose RocketMQ</a></p></li><li><p><strong>Do I need to install any other software in order to use RocketMQ, such as ZooKeeper?</strong></p><p>No，RocketMQ can run on independent。</p></li></ol><h2 class="anchor anchorWithStickyNavbar_LWe7" id="2-use">2 Use<a href="#2-use" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><ol><li><p><strong>Where does the newly created ConsumerGroup start consuming messages?</strong></p><p>1）When the 5.x SDK is first online, it will consume from the latest message on the server, starting from the tail of the queue. After restarting again, it will continue to consume from the last consumption position.</p><p>2）The 3.x/4.x SDK is more complicated. If the first start is within three days of the sent message, the consumer will start consuming from the first saved message on the server. If the sent message is more than three days, the consumer will start consuming from the latest message on the server, starting from the tail of the queue. After restarting again, it will continue to consume from the last consumption position.</p></li><li><p><strong>When consumption fails, how can the message be consumed again?</strong></p><p>1）In cluster mode, the consumption business logic code will return a consumption failure status, or throw an exception. If a message consumption fails, it will be retried according to the maximum retry count set, and then the message will be discarded.</p><p>2）In broadcast consumption mode, broadcast consumption still guarantees that the message is consumed at least once, but does not provide resend options.</p></li><li><p><strong>When consumption fails, how can the failed message be found?</strong></p><p>1）Using a time-based topic query can query messages within a period of time.</p><p>2）Use the topic and message ID to accurately query the message.</p><p>3）Use the topic and message Key to accurately query all messages with the same message Key.</p></li><li><p><strong>Is the message only delivered once?</strong></p><p>RocketMQ ensures that all messages are delivered at least once. In most cases, messages are not repeated.</p></li><li><p><strong>How can a new Broker be added?</strong></p><p>1）Start a new Broker and register it in the Broker list of the NameServer.</p><p>2）By default, only internal system Topics and Consumer Groups are automatically created. If you want to have your business topic and consumer group on the new node, copy them from the existing Broker. We provide management tools and command line to handle this.</p></li></ol><h2 class="anchor anchorWithStickyNavbar_LWe7" id="3-configuration-dependent">3 Configuration dependent<a href="#3-configuration-dependent" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><p>The following answers are default values, which can be modified through configuration.</p><ol><li><p><strong>How long can messages be saved on the server?</strong></p><p>Messages will be stored for a maximum of 3 days. Messages that have not been used for more than 3 days will be deleted.</p></li><li><p><strong>What is the size limit for message bodies?</strong></p><p>Typically, it is 256KB.</p></li><li><p><strong>How do you set the number of consumer threads?</strong></p><p>When you start the consumer, you can set the property. The parameter name varies by version.</p></li></ol><h2 class="anchor anchorWithStickyNavbar_LWe7" id="4-error">4 Error<a href="#4-error" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><ol><li><p><strong>APPLY_TOPIC_URL</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">topic[xxx] not exist, apply first please!</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></li><li><p><strong>reason</strong></p><p>1）When a Producer sends a message or a Consumer consumes a message, this exception will occur if the routing information for the Topic cannot be obtained.</p></li><li><p><strong>solution</strong></p><p>1）Make sure that the NameServer indeed contains the routing information for the Topic. You can use the management tool or the Web console to query the routing information from the NameServer through the TopicRoute;</p><p>2）Make sure that the Broker and Consumer are connected to the same NameServer cluster;</p><p>3）Make sure that the queue permissions for the topic are 6 (rw-) for the Producer or at least 2 (-w-) for the Consumer;</p><p>If the topic cannot be found, create it on the Broker through the management tool command updateTopic or the Web console.</p></li></ul></li><li><p><strong>NAME_SERVER_ADDR_NOT_EXIST_URL</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">No name server address, please set it</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p> or</p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">connect to xxx failed, maybe the domain name xxx not bind in /etc/hosts</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></li><li><p><strong>reason</strong></p><p>1）Producer or Consumer, there is an error in obtaining the NameServer address information.</p></li><li><p><strong>solution</strong></p><p>1）Please refer to：<a href="https://github.com/apache/rocketmq/blob/develop/docs/cn/best_practice.md" target="_blank" rel="noopener noreferrer">5.1 Client addressing</a></p></li></ul></li><li><p><strong>GROUP_NAME_DUPLICATE_URL</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">The producer group[xxx] has been created before, specify another name please.</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></li><li><p><strong>reason</strong></p><p>1）A Consumer Group with the same name has already been started and registration failed.</p></li><li><p><strong>solution</strong></p><p>1）Rename a new Consumer Group.</p><p>2）A Consumer Group with the same name was normally closed and then started again.</p></li></ul></li><li><p><strong>CLIENT_PARAMETER_CHECK_URL</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-text codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-text codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">consumerGroup can not equal ...</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>or</p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">allocateMessageQueueStrategy is null ...</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>or</p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">Long polling mode, the consumer consumerTimeoutMillisWhenSuspend must greater than brokerSuspendMaxTimeMillis ...</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>In addition to the above exceptions, there may be other exceptions that are not listed here.</p></li><li><p><strong>reason</strong></p><p>1）Consumer parameter verification failed.</p></li><li><p><strong>solution</strong></p><p>1）Please refer to： <a href="https://github.com/apache/rocketmq/blob/develop/docs/cn/best_practice.md" target="_blank" rel="noopener noreferrer">5.2 Client configuration</a></p></li></ul></li><li><p><strong>SUBSCRIPTION_GROUP_NOT_EXIST</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">subscription group not exist</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></li><li><p><strong>reason</strong></p><p>1）If the Consumer Group or DleayQueue encounters an error while getting subscription information.</p></li><li><p><strong>solution</strong></p><p>1）Ensure the Consumer's subscription to the Topic information is consistent with the Topic information in the NameServer.</p><p>2）Make sure the Broker and Consumer are connected to the same NameServer cluster.</p><p>3）Ensure the queue permissions for the Topic are 6 (rw-) for the Producer, or at least 2 (-w-) for the Consumer</p></li></ul></li><li><p><strong>CLIENT_SERVICE_NOT_OK</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">The xxx service state not OK, maybe started once</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></li><li><p><strong>reason</strong></p><p>1）Starting multiple Producer/Consumer instances in the same JVM using the same Producer/Consumer Group may cause the client to fail to start.</p></li><li><p><strong>solution</strong></p><p>1）Make sure only one Producer/Consumer instance is started for a given Producer/Consumer Group JVM.</p></li></ul></li><li><p><strong>NO_TOPIC_ROUTE_INFO</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">No route info of this topic:</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></li><li><p><strong>reason</strong></p><p>1）If a message is sent to a topic that is not available to the producer，that's what happens.</p></li><li><p><strong>solution</strong></p><p>1）Ensure the producer is able to connect to the name server and retrieve routing metadata from it.</p><p>2）Ensure the name server contains routing metadata for the topic. You can use a management tool or the Web console to query the routing metadata from the name server using TopicRoute.</p><p>3）Make sure your Broker is sending heartbeats to the same NameServer list that your producer is connected to.</p><p>4）Ensure the topic has permission 6 (rw-), or at least 2 (-w-).</p><p>If the topic is not found, create it on the Broker via the management tool command updateTopic or the Web console.</p></li></ul></li><li><p><strong>LOAD_JSON_EXCEPTION</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">readLocalOffset Exception</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></li><li><p><strong>reason</strong></p><p>1）In broadcast mode, consumers have an error when loading the local offsets.json file.</p><p>2）A damaged fastjson file can also cause the same problem.</p></li><li><p><strong>solution</strong></p><p>1）Check if the fastjson version and RocketMQ version in use are consistent.</p><p>2）Upgrade fastjson version.</p></li></ul></li><li><p><strong>SAME_GROUP_DIFFERENT_TOPIC</strong></p><ul><li><p><strong>exception information</strong></p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">the consumer's group info/subscription not exist</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></li><li><p><strong>reason</strong> |
