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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">Best Practice</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">Basic Best Practices</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>Basic Best Practices</h1><h2 class="anchor anchorWithStickyNavbar_LWe7" id="producer">Producer<a href="#producer" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="precautions-for-sending-messages">Precautions for sending messages<a href="#precautions-for-sending-messages" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><h4 class="anchor anchorWithStickyNavbar_LWe7" id="the-use-of-tags">The use of Tags<a href="#the-use-of-tags" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>An application can use a Topic, and message subtypes can be identified as tags. tags can be set freely by the application. Only when the producer sets tags when sending messages, the consumer can use tags to filter messages through the broker when subscribing to messages：message.setTags("TagA")。 </p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="the-use-of-keys">The use of Keys<a href="#the-use-of-keys" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>The unique identifier of each message at the service level must be set to the keys field to locate message loss problems in the future. The server creates an index (hash index) for each message, and the application can query the content of the message by topic and key, and by whom the message was consumed. Since it is a hash index, make sure that the key is as unique as possible to avoid potential hash collisions.</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"> // order Id </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> String orderId = "20034568923546"; </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> message.setKeys(orderId); </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><h4 class="anchor anchorWithStickyNavbar_LWe7" id="printing-logs">Printing Logs<a href="#printing-logs" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>The SendResult and key fields must be printed to print the message log if the message is sent successfully or failed. send Indicates that the message is sent successfully as long as no exception is thrown. There are multiple states for a successful send, defined in sendResult. Each state is described as follows: </p><ul><li><strong>SEND_OK</strong></li></ul><p>The message was sent successfully. Procedure Note that successful message delivery does not mean it is reliable. To ensure that no messages are lost, you should also enable the sync Master server or sync flush, which is SYNC_MASTER or SYNC_FLUSH.</p><ul><li><strong>FLUSH_DISK_TIMEOUT</strong></li></ul><p>The message is sent successfully but disk flushing times out. At this point, the message has entered the server queue (memory), only the server downtime, the message will be lost. In the message storage configuration parameters, you can set the disk flushing mode and the synchronization flush time. If the Broker server is set to FlushDiskType=SYNC_FLUSH (asynchronous flush by default), if the Broker server does not flush disks during the synchronous flush time (5s by default), The state, flush timeout, will be returned.</p><ul><li><strong>FLUSH_SLAVE_TIMEOUT</strong></li></ul><p>The message was sent successfully, but the server timed out when synchronizing the message to the Slave. At this point, the message has entered the server queue, only the server downtime, the message will be lost. If the role of the Broker server is SYNC_MASTER (ASYNC_MASTER by default) and the secondary Broker server does not complete synchronization with the primary server within the synchronization flush time (default: 5 seconds), This state is returned -- data synchronization to the Slave server has timed out.</p><ul><li><strong>SLAVE_NOT_AVAILABLE</strong></li></ul><p>The message was successfully sent, but the Slave was unavailable. Procedure At this point, the message has entered the Master server queue, only the Master server downtime, the message will be lost. If the role of the Broker server is SYNC_MASTER (ASYNC_MASTER by default) but no slave Broker server is configured, the broker returns the status that no Slave server is available.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="handling-method-for-message-sending-failure">Handling method for message sending failure<a href="#handling-method-for-message-sending-failure" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>The send method of Producer itself supports internal retry. The retry logic is as follows:</p><ul><li>Retry a maximum of two times (2 times for synchronous and 0 times for asynchronous).</li><li>If the delivery fails, it is routed to the next Broker. The total time for this method should not exceed the value set by sendMsgTimeout, which defaults to 10s.</li><li>If it sends a message to the broker that generates a timeout exception, it will not be retried.</li></ul><p>The above strategies also guarantee the success of message sending to a certain extent. If the service has high requirements on message reliability, you are advised to add retry logic. For example, if the send method fails to be invoked, the system tries to store the message to the db and retry periodically by the background thread to ensure that the message reaches the Broker.</p><p>The reason why the above db retry method is not integrated into the MQ client, but requires the application to complete by itself, is mainly based on the following considerations: First, the MQ client is designed as a stateless mode, convenient for arbitrary horizontal expansion, and the consumption of machine resources is only cpu, memory, network. Secondly, if the MQ client is internally integrated with a KV storage module, the data can only be reliable if the synchronous disk fall, and the synchronous disk fall itself has a large performance overhead, so it usually uses asynchronous disk fall, and because the application closure process is not controlled by MQ operation and maintenance personnel, it may often happen kill -9 such violent closure. Resulting in data not timely drop disk and loss. Third, the machine where the Producer resides has low reliability and is generally virtual machines, which are not suitable for storing important data. In summary, it is recommended that the retry process be controlled by the application.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="select-oneway-to-send">Select oneway to send<a href="#select-oneway-to-send" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>In general, a message is sent as follows:</p><ul><li>The client sends a request to the server</li><li>The server handles the request</li><li>The server returns a reply to the client</li></ul><p>Therefore, the time taken to send a message is the sum of the above three steps. However, some scenarios require a very short time, but do not have high reliability requirements. For example, log collection applications can be invoked in oneway mode. On the client side, sending a request is only the cost of a system call of the operating system, that is, writing data to the socket buffer of the client, which usually takes microseconds.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="client-configuration">Client Configuration<a href="#client-configuration" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><p>In contrast to RocketMQ's cluster of brokers, both producers and consumers are clients. This section describes the behavior configuration common to producers and consumers.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="client-addressing-mode">Client addressing mode<a href="#client-addressing-mode" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>RocketMQ enables clients to find NameServer and then NameServer to find Broker. As shown in the following figure, the configuration mode ranges from high to low. The higher priority overrides the lower priority.</p><ul><li>The NameServer address is specified in the code, and multiple NameServer addresses are separated by semicolons </li></ul><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">producer.setNamesrvAddr("192.168.0.1:9876;192.168.0.2:9876"); </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">consumer.setNamesrvAddr("192.168.0.1:9876;192.168.0.2:9876");</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><ul><li>The NameServer address is specified in the Java startup parameter</li></ul><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">-Drocketmq.namesrv.addr=192.168.0.1:9876;192.168.0.2:9876 </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><ul><li>The environment variable specifies the NameServer address</li></ul><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">export NAMESRV_ADDR=192.168.0.1:9876;192.168.0.2:9876 </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><ul><li>HTTP static server addressing (default)</li></ul><p>After the client is started, it periodically accesses a static HTTP server with the following address:<a href="http://jmenv.tbsite.net:8080/rocketmq/nsaddr" target="_blank" rel="noopener noreferrer">http://jmenv.tbsite.net:8080/rocketmq/nsaddr</a>，The URL returns something like this:</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">192.168.0.1:9876;192.168.0.2:9876 </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>By default, the client accesses the HTTP server every 2 minutes and updates the local NameServer address. | |
| The URL is hardcoded in the code. You can change the server to be accessed by modifying the /etc/hosts file, for example, adding the following configuration to /etc/hosts:</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">10.232.22.67 jmenv.taobao.net </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>Static HTTP server addressing is recommended. It is easy to deploy clients and the NameServer cluster can be hot upgraded.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="consumer">Consumer<a href="#consumer" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="the-consumption-process-is-idempotent">The consumption process is idempotent<a href="#the-consumption-process-is-idempotent" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>RocketMQ cannot avoid message duplications (Exactly Once), so if the business is very sensitive to consumption duplications, it is important to de-process at the business level. | |
| This can be done with the help of relational databases. You first need to determine a unique key for the message, either an msgId or a unique identifying field in the message content, such as an order id. | |
| Determine if the unique key exists in the relational database before consumption. If not, insert and consume, otherwise skip. (The actual process should consider the atomicity problem, determine whether there is a primary key conflict, then the insertion failed, directly skip)</p><p>MsgId must be a globally unique identifier, but in practice, there may be cases where the same message has two different msgIds (consumer active retransmission, duplication due to client reinvestment mechanism, etc.), which necessitates repeated consumption of business fields.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="a-slow-process-of-consumption">A slow process of consumption<a href="#a-slow-process-of-consumption" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><h3 class="anchor anchorWithStickyNavbar_LWe7" id="increase-consumption-parallelism">Increase consumption parallelism<a href="#increase-consumption-parallelism" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>The vast majority of message consumption is IO intensive, that is, it may be operating on a database or calling an RPC, and the rate of consumption for this type of consumption depends on the throughput of the back-end database or external system. | |
| By increasing consumption parallelism, the total consumption throughput can be improved, but when the parallelism increases to a certain degree, it will decrease. | |
| Therefore, the application must set a reasonable degree of parallelism. There are several ways to modify consumption parallelism:</p><ul><li>In the same ConsumerGroup, we increase the number of Consumer instances to improve parallelism (note that Consumer instances exceeding the subscription queue are invalid). You can add a machine, or start multiple processes on an existing machine.</li><li>Improve the consumption parallel thread of a single Consumer by modifying parameters consumeThreadMin and consumeThreadMax.</li></ul><h3 class="anchor anchorWithStickyNavbar_LWe7" id="consumption-in-bulk">Consumption in bulk<a href="#consumption-in-bulk" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>If some business processes support batch consumption, the consumption throughput can be greatly improved. For example, the application of order deduction takes 1 s to process one order at a time, and only 2 s to process 10 orders at a time. In this way, the consumption throughput can be greatly improved. | |
| By setting the consumer consumeMessageBatchMaxSize return a parameter, the default is 1, namely consumption one message, for example, is set to N, so the number of messages every time consumption less than or equal to N.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="skip-non-important-messages">Skip non-important messages<a href="#skip-non-important-messages" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>In case of message pile-up, if the consumption rate cannot keep up with the delivery rate, and if the business is not demanding enough data, you can choose to discard unimportant messages. | |
| For example, when a queue accumulates more than 100,000 messages, try to discard some or all of them so that you can quickly catch up with sending messages. Example code is as follows:</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"> public ConsumeConcurrentlyStatus consumeMessage(</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> List<MessageExt> msgs,</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> ConsumeConcurrentlyContext context) {</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> long offset = msgs.get(0).getQueueOffset();</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> String maxOffset =</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> msgs.get(0).getProperty(Message.PROPERTY_MAX_OFFSET);</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> long diff = Long.parseLong(maxOffset) - offset;</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> if (diff > 100000) {</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> // TODO Special handling of message stacking cases</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> }</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> // TODO Normal consumption process</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> } </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><h4 class="anchor anchorWithStickyNavbar_LWe7" id="optimize-the-per-message-consumption-process">Optimize the per-message consumption process<a href="#optimize-the-per-message-consumption-process" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>For example, the consumption process of a message is as follows:</p><ul><li>Query <!-- -->[data 1]<!-- --> from DB according to message</li><li>Query <!-- -->[data 2]<!-- --> from DB according to message</li><li>Complex business calculations</li><li>Insert <!-- -->[data 3]<!-- --> into DB</li><li>Insert <!-- -->[data 4]<!-- --> into DB</li></ul><p>There are four interactions with DB during the consumption of this message. If we calculate each interaction as 5ms, the total time is 20ms. | |
| Assuming that the service computation takes 5ms, the total time is 25ms. Therefore, if the four DB interactions can be optimized to two, the total time can be optimized to 15ms, which means that the overall performance is improved by 40%. | |
| Therefore, if the application is sensitive to delay, the DB can be deployed on SSD disks. Compared with SCSI disks, the RT of the former is much smaller.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="consumption-print-log">Consumption print log<a href="#consumption-print-log" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p>If the number of messages is small, you are advised to print messages in the consumption entry method, which takes a long time to consume.</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"> public ConsumeConcurrentlyStatus consumeMessage(</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> List<MessageExt> msgs,</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> ConsumeConcurrentlyContext context) {</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> log.info("RECEIVE_MSG_BEGIN: " + msgs.toString());</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> // TODO Normal consumption process</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> } </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>If you can print each message consuming time, it will be more convenient to troubleshoot online problems such as slow consumption.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="other-consumption-tips">Other Consumption Tips<a href="#other-consumption-tips" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><h4 class="anchor anchorWithStickyNavbar_LWe7" id="about-consumers-and-subscriptions">About consumers and subscriptions<a href="#about-consumers-and-subscriptions" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>The first thing to note is that different consumer groups can consume several topics independently, and each consumer group has its own consumption offset. Make sure that the subscription information of each consumer within the same group is consistent.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="about-ordered-messages">About Ordered Messages<a href="#about-ordered-messages" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>Consumers will lock each message queue to ensure that they are consumed one by one, which causes performance degradation, but is useful when you are concerned about message order. We do not recommend throwing an exception, you can return ConsumeOrderlyStatus. SUSPEND_CURRENT_QUEUE_A_MOMENT instead.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="about-concurrent-consumption">About Concurrent consumption<a href="#about-concurrent-consumption" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>As the name suggests, the consumer will concurrent consumption of these messages, it is recommended that you use it to get good performance, we do not recommend throwing an exception, you can return ConsumeConcurrentlyStatus.RECONSUME_LATER instead.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="consume-status-is-about-consumption-status">Consume Status is about consumption status<a href="#consume-status-is-about-consumption-status" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>For concurrent consumption listeners, you can return RECONSUME_LATER to notify the consumer that the message cannot be consumed now and that it is expected to be consumed again later. | |
| You can then continue consuming other messages. For an ordered message listener, you can't skip the message because you care about its order, but you can go back to SUSPEND_CURRENT_QUEUE_A_MOMENT and tell the consumer to wait.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="about-blocking">About Blocking<a href="#about-blocking" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>Blocking listeners is not recommended because it blocks the thread pool and may eventually terminate the consuming process</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="about-thread-count-settings">About thread count Settings<a href="#about-thread-count-settings" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>Consumers use ThreadPoolExecutor to consume messages internally, so you can change it by setting setConsumeThreadMin or setConsumeThreadMax.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="about-the-consumption-position">About the consumption position<a href="#about-the-consumption-position" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h4><p>When creating a new consumer group, you need to decide whether you want to consume the history messages already in the Broker. CONSUME_FROM_LAST_OFFSET will ignore the history messages and consume any messages generated later. | |
| CONSUME_FROM_FIRST_OFFSET will consume every information that exists in the Broker. You can also use CONSUME_FROM_TIMESTAMP to consume messages generated after a specified timestamp.</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><h3 class="anchor anchorWithStickyNavbar_LWe7" id="broker-role">Broker Role<a href="#broker-role" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p> Broker roles are classified into ASYNC_MASTER, SYNC_MASTER, and SLAVE. | |
| If you have strict requirements on message reliability, deploy SYNC_MASTER plus SLAVE. | |
| If message reliability is not required, deploy ASYNC_MASTER plus SLAVE. | |
| If testing is only convenient, you can select ASYNC_MASTER only or SYNC_MASTER only deployment.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="flushdisktype">FlushDiskType<a href="#flushdisktype" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><p> Compared with ASYNC_FLUSH, SYNC_FLUSH suffers from performance loss but is more reliable. Therefore, the trade-off must be made based on the actual service scenario.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="broker-configuration">Broker Configuration<a href="#broker-configuration" class="hash-link" aria-label="Direct link to heading" title="Direct link to heading"></a></h3><table><thead><tr><th>Parameter</th><th>Default</th><th>Description</th></tr></thead><tbody><tr><td>listenPort</td><td>10911</td><td>A listening port that accepts client connections</td></tr><tr><td>namesrvAddr</td><td>null</td><td>nameServer address</td></tr><tr><td>brokerIP1</td><td>The network InetAddress</td><td>The IP address on which the broker is currently listening</td></tr><tr><td>brokerIP2</td><td>same to brokerIP1</td><td>When a master/slave broker exists, if the brokerIP2 property is configured on the broker master node, the broker slave node will connect to the brokerIP2 configured on the master node for synchronization</td></tr><tr><td>brokerName</td><td>null</td><td>broker name</td></tr><tr><td>brokerClusterName</td><td>DefaultCluster</td><td>The Cluser name to which this broker belongs</td></tr><tr><td>brokerId</td><td>0</td><td>broker id 0 indicates master, and other positive integers indicate slave</td></tr><tr><td>storePathCommitLog</td><td>$HOME/store/commitlog/</td><td>Path to store the commit log</td></tr><tr><td>storePathConsumerQueue</td><td>$HOME/store/consumequeue/</td><td>A path that consumes queue is stored</td></tr><tr><td>mapedFileSizeCommitLog</td><td>1024 <em> 1024 </em> 1024(1G)</td><td>commit log mapping file size</td></tr><tr><td>deleteWhen</td><td>04</td><td>At what time of day should I delete the commit log whose file retention time has exceeded</td></tr><tr><td>fileReservedTime</td><td>72</td><td>File retention time in hours</td></tr><tr><td>brokerRole</td><td>ASYNC_MASTER</td><td>SYNC_MASTER/ASYNC_MASTER/SLAVE</td></tr><tr><td>flushDiskType</td><td>ASYNC_FLUSH</td><td>SYNC_FLUSH/ASYNC_FLUSH The broker in SYNC_FLUSH mode guarantees to flush messages before receiving the acknowledged producer. ASYNC_FLUSH brokers use the flush mode to flush a group of messages for better performance.</td></tr></tbody></table></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/05-bestPractice/01bestpractice.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/deployment/04Exporter"><div 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