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19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .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">功能特性</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">消息发送重试和流控机制</span><meta itemprop="position" content="2"></li></ul></nav><span class="theme-doc-version-badge badge badge--secondary">版本：5.0</span><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">本页总览</button></div><div class="theme-doc-markdown markdown"><h1>消息发送重试和流控机制</h1><p>本文为您介绍 Apache RocketMQ 的消息发送重试机制和消息流控机制。</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="背景信息">背景信息<a href="#背景信息" class="hash-link" aria-label="背景信息的直接链接" title="背景信息的直接链接"></a></h2><p><strong>消息发送重试</strong></p><p>Apache RocketMQ的消息发送重试机制主要为您解答如下问题：</p><ul><li><p>部分节点异常是否影响消息发送？</p></li><li><p>请求重试是否会阻塞业务调用？</p></li><li><p>请求重试会带来什么不足？</p></li></ul><p><strong>消息流控</strong></p><p>Apache RocketMQ 的流控机制主要为您解答如下问题：</p><ul><li><p>系统在什么情况下会触发流控？</p></li><li><p>触发流控时客户端行为是什么？</p></li><li><p>应该如何避免触发流控，以及如何应对突发流控？</p></li></ul><h2 class="anchor anchorWithStickyNavbar_LWe7" id="消息发送重试机制">消息发送重试机制<a href="#消息发送重试机制" class="hash-link" aria-label="消息发送重试机制的直接链接" title="消息发送重试机制的直接链接"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="重试基本概念">重试基本概念<a href="#重试基本概念" class="hash-link" aria-label="重试基本概念的直接链接" title="重试基本概念的直接链接"></a></h3><p>Apache RocketMQ 客户端连接服务端发起消息发送请求时，可能会因为网络故障、服务异常等原因导致调用失败。为保证消息的可靠性， Apache RocketMQ 在客户端SDK中内置请求重试逻辑，尝试通过重试发送达到最终调用成功的效果。</p><p>同步发送和异步发送模式均支持消息发送重试。</p><p><strong>重试触发条件</strong></p><p>触发消息发送重试机制的条件如下：</p><ul><li><p>客户端消息发送请求调用失败或请求超时</p></li><li><p>网络异常造成连接失败或请求超时。</p></li><li><p>服务端节点处于重启或下线等状态造成连接失败。</p></li><li><p>服务端运行慢造成请求超时。</p></li><li><p>服务端返回失败错误码</p><ul><li><p>系统逻辑错误：因运行逻辑不正确造成的错误。</p></li><li><p>系统流控错误：因容量超限造成的流控错误。</p></li></ul></li></ul><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>备注</div><div class="admonitionContent_S0QG"><p>对于事务消息，只会进行<a href="https://github.com/grpc/proposal/blob/master/A6-client-retries.md#transparent-retries" target="_blank" rel="noopener noreferrer">透明重试（transparent retries）</a>，网络超时或异常等场景不会进行重试。</p></div></div><h3 class="anchor anchorWithStickyNavbar_LWe7" id="重试流程">重试流程<a href="#重试流程" class="hash-link" aria-label="重试流程的直接链接" title="重试流程的直接链接"></a></h3><p>生产者在初始化时设置消息发送最大重试次数，当出现上述触发条件的场景时，生产者客户端会按照设置的重试次数一直重试发送消息，直到消息发送成功或达到最大重试次数重试结束，并在最后一次重试失败后返回调用错误响应。</p><ul><li><p>同步发送：调用线程会一直阻塞，直到某次重试成功或最终重试失败，抛出错误码和异常。</p></li><li><p>异步发送：调用线程不会阻塞，但调用结果会通过异常事件或者成功事件返回。</p></li></ul><h3 class="anchor anchorWithStickyNavbar_LWe7" id="重试间隔">重试间隔<a href="#重试间隔" class="hash-link" aria-label="重试间隔的直接链接" title="重试间隔的直接链接"></a></h3><ul><li><p>除服务端返回系统流控错误场景，其他触发条件触发重试后，均会立即进行重试，无等待间隔。</p></li><li><p>若由于服务端返回流控错误触发重试，系统会按照指数退避策略进行延迟重试。指数退避算法通过以下参数控制重试行为：</p><ul><li><p>INITIAL_BACKOFF： 第一次失败重试前后需等待多久，默认值：1秒。</p></li><li><p>MULTIPLIER ：指数退避因子，即退避倍率，默认值：1.6。</p></li><li><p>JITTER ：随机抖动因子，默认值：0.2。</p></li><li><p>MAX_BACKOFF ：等待间隔时间上限，默认值：120秒</p></li><li><p>MIN_CONNECT_TIMEOUT ：最短重试间隔，默认值：20秒。</p></li></ul></li></ul><p><strong>建议算法如下：</strong></p><div class="language-unknow codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-unknow codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token plain">ConnectWithBackoff()</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> current_backoff = INITIAL_BACKOFF</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> current_deadline = now() + INITIAL_BACKOFF</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> while (TryConnect(Max(current_deadline, now() + MIN_CONNECT_TIMEOUT))!= SUCCESS)</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> SleepUntil(current_deadline)</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> current_backoff = Min(current_backoff * MULTIPLIER, MAX_BACKOFF)</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> current_deadline = now() + current_backoff + UniformRandom(-JITTER * current_backoff, JITTER * current_backoff)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="复制代码到剪贴板" title="复制" 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> 更多信息，请参见<a href="https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md" target="_blank" rel="noopener noreferrer">connection-backoff 策略</a>。</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="功能约束">功能约束<a href="#功能约束" class="hash-link" aria-label="功能约束的直接链接" title="功能约束的直接链接"></a></h3><ul><li><p>链路耗时阻塞评估：从上述重试机制可以看出，在重试流程中生产者仅能控制最大重试次数。若由于系统异常触发了SDK内置的重试逻辑，则服务端需要等待最终重试结果，可能会导致消息发送请求链路被阻塞。对于某些实时调用类场景，您需要合理评估每次调用请求的超时时间以及最大重试次数，避免影响全链路的耗时。</p></li><li><p>最终异常兜底： Apache RocketMQ 客户端内置的发送请求重试机制并不能保证消息发送一定成功。当最终重试仍然失败时，业务方调用需要捕获异常，并做好冗余保护处理，避免消息发送结果不一致。</p></li><li><p>消息重复问题：因远程调用的不确定性，当Apache RocketMQ客户端因请求超时触发消息发送重试流程，此时客户端无法感知服务端的处理结果，客户端进行的消息发送重试可能会产生消息重复问题，业务逻辑需要自行处理消息重复问题。</p></li></ul><h2 class="anchor anchorWithStickyNavbar_LWe7" id="消息流控机制">消息流控机制<a href="#消息流控机制" class="hash-link" aria-label="消息流控机制的直接链接" title="消息流控机制的直接链接"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="消息流控基本概念">消息流控基本概念<a href="#消息流控基本概念" class="hash-link" aria-label="消息流控基本概念的直接链接" title="消息流控基本概念的直接链接"></a></h3><p>消息流控指的是系统容量或水位过高， Apache RocketMQ 服务端会通过快速失败返回流控错误来避免底层资源承受过高压力。</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="触发条件">触发条件<a href="#触发条件" class="hash-link" aria-label="触发条件的直接链接" title="触发条件的直接链接"></a></h3><p>Apache RocketMQ 的消息流控触发条件如下：</p><ul><li><p>存储压力大：参考<a href="/zh/docs/featureBehavior/09consumerprogress">消费进度管理</a>的原理机制，消费者分组的初始消费位点为当前队列的最大消费位点。若某些场景例如业务上新等需要回溯到指定时刻前开始消费，此时队列的存储压力会瞬间飙升，触发消息流控。</p></li><li><p>服务端请求任务排队溢出：若消费者消费能力不足，导致队列中有大量堆积消息，当堆积消息超过一定数量后会触发消息流控，减少下游消费系统压力。</p></li></ul><h3 class="anchor anchorWithStickyNavbar_LWe7" id="流控行为">流控行为<a href="#流控行为" class="hash-link" aria-label="流控行为的直接链接" title="流控行为的直接链接"></a></h3><p>当系统触发消息发送流控时，客户端会收到系统限流错误和异常，错误码信息如下：</p><ul><li><p>reply-code：530</p></li><li><p>reply-text：TOO_MANY_REQUESTS</p></li></ul><p>客户端收到系统流控错误码后，会根据指数退避策略进行消息发送重试。</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="处理建议">处理建议<a href="#处理建议" class="hash-link" aria-label="处理建议的直接链接" title="处理建议的直接链接"></a></h3><ul><li><p>如何避免触发消息流控：触发限流的根本原因是系统容量或水位过高，您可以利用可观测性功能监控系统水位容量等，保证底层资源充足，避免触发流控机制。</p></li><li><p>突发消息流控处理：如果因为突发原因触发消息流控，且客户端内置的重试流程执行失败，则建议业务方将请求调用临时替换到其他系统进行应急处理。</p></li></ul></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/versioned_docs/version-5.0/04-featureBehavior/05sendretrypolicy.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" 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