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Firstly, we assume that Messageâs isWaitStoreMsgOK=true(default is true). If not, we will always get SEND_OK if no exception is thrown. +Follow are the descriptions about each status.</p> +<h3 id="flush_disk_timeout">FLUSH_DISK_TIMEOUT</h3> +<p>If the Broker set MessageStoreConfigâs FlushDiskType=SYNC_FLUSH(default is ASYNC_FLUSH), and the Broker dose not finish flushing disk within MessageStoreConfigâs syncFlushTimeout(default is 5 secs), you will get such status.</p> +<h3 id="flush_slave_timeout">FLUSH_SLAVE_TIMEOUT</h3> +<p>If the Brokerâs role is SYNC_MASTER(default is ASYNC_MASTER), and the slave Broker dose not finish synchronizing with the master within the MessageStoreConfigâs syncFlushTimeout(default is 5 secs), you will get such status.</p> +<h3 id="slave_not_available">SLAVE_NOT_AVAILABLE</h3> +<p>If the Brokerâs role is SYNC_MASTER(default is ASYNC_MASTER), but no slave Broker is configured, you will get such status.</p> +<h3 id="send_ok">SEND_OK</h3> +<p>You should be aware that SEND_OK does not mean it is reliable. If you cannot tolerate message missing, you should also enable SYNC_MASTER or SYNC_FLUSH.</p> +<h3 id="duplication-or-missing">Duplication or Missing</h3> +<p>If you get FLUSH_DISK_TIMEOUT, FLUSH_SLAVE_TIMEOUT and the Broker happens to shutdown right the moment, you may get your message missing. +At this time, you have two choices, one is letting it go, which may get message missing; another is resending, which may get message duplication. +Often we suggest resend and make a way to handle the duplication removal when consuming. Unless you feel it does not matter when some messages are missed. +But be ware that resending has no use when you get SLAVE_NOT_AVAILABLE, youâd better keep the scene and send some alerts to the Cluster Manager.</p> +<h2 id="timeout">Timeout</h2> +<p>The Client send requests to Broker, and wait the responses, but if the max wait time is elapsed and no response is return, the Client will throw a RemotingTimeoutException. +The default wait time is 3 seconds.You can also pass timeout argument using send(msg, timeout) instead of send(msg). +Note that we do not suggest the value to be too small, for the Broker need some time to flush disk or synchronize with slave. Also the value may have little effect if it is too bigger than syncFlushTimeout for Broker may return a response with FLUSH_SLAVE_TIMEOUT or FLUSH_SLAVE_TIMEOUT before the timeout.</p> +<h2 id="message-size">Message Size</h2> +<p>We suggest the message should be no more than 512K.</p> +<h2 id="async-sending">Async Sending</h2> +<p>Default send(msg) will block until the response is return. So if you care about performance, we suggest you use send(msg, callback) which will act in a async way.</p> +<h2 id="producer-group">Producer Group</h2> +<p>Normally, the producer group has no effects. But if you are involved in transaction, you should pay attention to it. +In default, you can only create only one producer with the same producer group in the same JVM. Usually, this is enough.</p> +<h2 id="thread-safety">Thread Safety</h2> +<p>The producer is thread-safe, you can just use it in your business logic.</p> +<h2 id="performance">Performance</h2> +<p>If you want more than one producer in one JVM, maybe for big data processing, we suggest you:</p> +<ul> + <li>use async sending with a few producers(3~5 is enough)</li> + <li>setInstanceName for each producer</li> +</ul> + + + + </section> + + <footer class="page__meta"> + + + + + + <p class="page__date"><strong><i class="fa fa-fw fa-calendar" aria-hidden="true"></i> Updated:</strong> <time datetime="2016-12-25">December 25, 2016</time></p> + + </footer> + + <section class="page__share"> + + <h4 class="page__share-title">Share on</h4> + + + <a href="https://twitter.com/intent/tweet?via=ApacheRocketMQ&text=Best Practice For Producer /docs/best-practice-producer/" class="btn btn--twitter" title="Share on Twitter"><i class="fa fa-fw fa-twitter" aria-hidden="true"></i><span> Twitter</span></a> + + <a href="https://www.facebook.com/sharer/sharer.php?u=/docs/best-practice-producer/"; class="btn btn--facebook" title="Share on Facebook"><i class="fa fa-fw fa-facebook" aria-hidden="true"></i><span> Facebook</span></a> + + <a href="https://plus.google.com/share?url=/docs/best-practice-producer/"; class="btn btn--google-plus" title="Share on Google Plus"><i class="fa fa-fw fa-google-plus" aria-hidden="true"></i><span> Google+</span></a> + + <a href="https://www.linkedin.com/shareArticle?mini=true&url=/docs/best-practice-producer/"; class="btn btn--linkedin" title="Share on LinkedIn"><i class="fa fa-fw fa-linkedin" aria-hidden="true"></i><span> LinkedIn</span></a> +</section> + + + + <nav class="pagination"> + + <a href="/docs/best-practice-namesvr/" class="pagination--pager" title="Best Practice For NameServer +">Previous</a> + + + <a href="#" class="pagination--pager disabled">Next</a> + + </nav> + + </div> + + + <div class="page__comments"> + + + <h4 class="page__comments-title">Leave a Comment</h4> + <section id="disqus_thread"></section> + +</div> + + </article> + + + +</div> + + <div class="page__footer"> + <footer> + <!-- start custom footer snippets --> + +<!-- end custom footer snippets --> + <div class="page__footer-follow"> + <ul class="social-icons"> + + <li><strong>Follow:</strong></li> + + + <li><a href="https://twitter.com/ApacheRocketMQ";><i class="fa fa-fw fa-twitter-square" aria-hidden="true"></i> Twitter</a></li> + + + + <li><a href="http://github.com/apache/incubator-rocketmq";><i class="fa fa-fw fa-github" aria-hidden="true"></i> GitHub</a></li> + + + <li><a href="/feed.xml"><i class="fa fa-fw fa-rss-square" aria-hidden="true"></i> Feed</a></li> + </ul> +</div> + +<div class="page__footer-copyright">Copyright © 2017 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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Please <a href="http://browsehappy.com/";>upgrade your browser</a> to improve your experience.</div> +<![endif]--> + <div class="masthead"> + <div class="masthead__inner-wrap"> + <div class="masthead__menu"> + <nav id="site-nav" class="greedy-nav"> + <button><div class="navicon"></div></button> + <ul class="visible-links"> + <li class="masthead__menu-item masthead__menu-item--lg"><a href="/">Apache RocketMQ</a></li> + + + <li class="masthead__menu-item"><a href="/docs/quick-start/">Documentation</a></li> + + + <li class="masthead__menu-item"><a href="/year-archive/">Blog</a></li> + + + <li class="masthead__menu-item"><a href="/community/">Community</a></li> + + + <li class="masthead__menu-item"><a href="/about/team/">About</a></li> + + </ul> + <ul class="hidden-links hidden"></ul> + </nav> + </div> + </div> +</div> + + + + + +<div id="main" role="main"> + + <div class="sidebar sticky"> + + + + + + + + + + +<nav class="nav__list"> + + <input id="ac-toc" name="accordion-toc" type="checkbox" /> + <label for="ac-toc">Toggle Menu</label> + <ul class="nav__items"> + + <li> + + <span class="nav__sub-title">User Guide</span> + + + + <ul> + + + + + + + + <li><a href="/docs/quick-start/" class="">Quick Start</a></li> + + + + + + + + <li><a href="/docs/motivation/" class="">Motivation</a></li> + + + + + + + + <li><a href="/docs/core-concept/" class="">Core Concept</a></li> + + + + + + + + <li><a href="/docs/cli-admin-tool/" class="active">CLI Admin Tool</a></li> + + + + + + + + <li><a href="/docs/cluster-deployment/" class="">Cluster Configuration & Deployment</a></li> + + </ul> + + </li> + + <li> + + <span class="nav__sub-title">Contributor Guide</span> + + + + <ul> + + + + + + + + <li><a href="/docs/code-guidelines/" class="">Code Guidelines</a></li> + + + + + + + + <li><a href="/docs/pull-request/" class="">Best Practice in PR</a></li> + + </ul> + + </li> + + <li> + + <span class="nav__sub-title">Best Practice</span> + + + + <ul> + + + + + + + + <li><a href="/docs/best-practice-broker/" class="">Broker</a></li> + + + + + + + + <li><a href="/docs/best-practice-producer/" class="">Producer</a></li> + + + + + + + + <li><a href="/docs/best-practice-consumer/" class="">Consumer</a></li> + + + + + + + + <li><a href="/docs/best-practice-namesvr/" class="">NameServer</a></li> + + </ul> + + </li> + + <li> + + + + + <a href="/docs/faq/"><span class="nav__sub-title">FAQ</span></a> + + + + </li> + + </ul> +</nav> + + + </div> + + + <article class="page" itemscope itemtype="http://schema.org/CreativeWork";> + <meta itemprop="headline" content="CLI Admin Tool"> + <meta itemprop="description" content="RocketMQ provides a CLI admin tool belt to query, manage and diagnose various issues."> + <meta itemprop="datePublished" content="January 24, 2017"> + <meta itemprop="dateModified" content="December 17, 2016"> + + <div class="page__inner-wrap"> + + <header> + <h1 class="page__title" itemprop="headline">CLI Admin Tool +</h1> + + </header> + + + <section class="page__content" itemprop="text"> + <p>RocketMQ provides a CLI admin tool belt to query, manage and diagnose various issues.</p> + +<aside class="sidebar__right"> +<nav class="toc"> + <header><h4 class="nav__title"><i class="fa fa-file-text"></i> On This Page</h4></header> +<ul class="toc__menu" id="markdown-toc"> + <li><a href="#prerequisite" id="markdown-toc-prerequisite">Prerequisite</a></li> + <li><a href="#how-to-get-it" id="markdown-toc-how-to-get-it">How To Get it</a></li> + <li><a href="#how-to-use" id="markdown-toc-how-to-use">How to use</a></li> + <li><a href="#command-manual" id="markdown-toc-command-manual">Command Manual</a></li> +</ul> + + </nav> +</aside> + +<h1 id="prerequisite">Prerequisite</h1> + +<p>Make sure you have walked through <a href="/docs/quick-start/">Quick Start</a> and <a href="/docs/core-concept/">Core Concept</a> sections.</p> + +<h1 id="how-to-get-it">How To Get it</h1> + +<p>The admin tool is shipped along with RocketMQ. Either you download a pre-built binary version or build from source by yourself, you already have it.</p> + +<p>In case you have source code, the <a href="https://github.com/alibaba/RocketMQ/tree/master/rocketmq-tools";>rocketmq-tools module</a> contains its source code.</p> + +<h1 id="how-to-use">How to use</h1> + +<p>The Admin Tool is very easy to use. Here, for demonstration purpose, *nix environment is assumed.</p> + +<p>Change directory to ${PACKAGE}/bin, command <code class="highlighter-rouge">bash mqadmin</code>, you should see the following help menu pops out.</p> + +<div class="highlighter-rouge"><pre class="highlight"><code>The most commonly used mqadmin commands are: + updateTopic Update or create topic + deleteTopic Delete topic from broker and NameServer. + updateSubGroup Update or create subscription group + deleteSubGroup Delete subscription group from broker. + updateBrokerConfig Update broker's config + updateTopicPerm Update topic perm + topicRoute Examine topic route info + topicStatus Examine topic Status info + topicClusterList get cluster info for topic + brokerStatus Fetch broker runtime status data + queryMsgById Query Message by Id + queryMsgByKey Query Message by Key + queryMsgByUniqueKey Query Message by Unique key + queryMsgByOffset Query Message by offset + queryMsgByUniqueKey Query Message by Unique key + printMsg Print Message Detail + sendMsgStatus send msg to broker. + brokerConsumeStats Fetch broker consume stats data + producerConnection Query producer's socket connection and client version + consumerConnection Query consumer's socket connection, client version and subscription + consumerProgress Query consumers's progress, speed + consumerStatus Query consumer's internal data structure + cloneGroupOffset clone offset from other group. + clusterList List all of clusters + topicList Fetch all topic list from name server + updateKvConfig Create or update KV config. + deleteKvConfig Delete KV config. + wipeWritePerm Wipe write perm of broker in all name server + resetOffsetByTime Reset consumer offset by timestamp(without client restart). + updateOrderConf Create or update or delete order conf + cleanExpiredCQ Clean expired ConsumeQueue on broker. + cleanUnusedTopic Clean unused topic on broker. + startMonitoring Start Monitoring + statsAll Topic and Consumer tps stats + syncDocs Synchronize wiki and issue to github.com + allocateMQ Allocate MQ + checkMsgSendRT check message send response time + clusterRT List All clusters Message Send RT + +See 'mqadmin help <command>' for more information on a specific command. +</code></pre> +</div> + +<p>As you see, the most commonly used commands are listed with a brief description. To get detailed manual of each command, <code class="highlighter-rouge">bash mqadmin help <command></code>. For example, command <code class="highlighter-rouge">bash mqadmin help clusterList</code> will bring out the following help text:</p> + +<div class="highlighter-rouge"><pre class="highlight"><code>usage: mqadmin clusterList [-h] [-i <arg>] [-m] [-n <arg>] + -h,--help Print help + -i,--interval <arg> specify intervals numbers, it is in seconds + -m,--moreStats Print more stats + -n,--namesrvAddr <arg> Name server address list, eg: 192.168.0.1:9876;192.168.0.2:9876 +</code></pre> +</div> + +<p>The help text lists possible options and interpretation of each option.</p> + +<h1 id="command-manual">Command Manual</h1> + + + </section> + + <footer class="page__meta"> + + + + + + <p class="page__date"><strong><i class="fa fa-fw fa-calendar" aria-hidden="true"></i> Updated:</strong> <time datetime="2016-12-17">December 17, 2016</time></p> + + </footer> + + <section class="page__share"> + + <h4 class="page__share-title">Share on</h4> + + + <a href="https://twitter.com/intent/tweet?via=ApacheRocketMQ&text=CLI Admin Tool /docs/cli-admin-tool/" class="btn btn--twitter" title="Share on Twitter"><i class="fa fa-fw fa-twitter" aria-hidden="true"></i><span> Twitter</span></a> + + <a href="https://www.facebook.com/sharer/sharer.php?u=/docs/cli-admin-tool/"; class="btn btn--facebook" title="Share on Facebook"><i class="fa fa-fw fa-facebook" aria-hidden="true"></i><span> Facebook</span></a> + + <a href="https://plus.google.com/share?url=/docs/cli-admin-tool/"; class="btn btn--google-plus" title="Share on Google Plus"><i class="fa fa-fw fa-google-plus" aria-hidden="true"></i><span> Google+</span></a> + + <a href="https://www.linkedin.com/shareArticle?mini=true&url=/docs/cli-admin-tool/"; class="btn btn--linkedin" title="Share on LinkedIn"><i class="fa fa-fw fa-linkedin" aria-hidden="true"></i><span> LinkedIn</span></a> +</section> + + + + <nav class="pagination"> + + <a href="/docs/core-concept/" class="pagination--pager" title="Core Concept +">Previous</a> + + + <a href="/docs/cluster-deployment/" class="pagination--pager" title="Cluster Configuration and Deployment +">Next</a> + + </nav> + + </div> + + + <div class="page__comments"> + + + <h4 class="page__comments-title">Leave a Comment</h4> + <section id="disqus_thread"></section> + +</div> + + </article> + + + +</div> + + <div class="page__footer"> + <footer> + <!-- start custom footer snippets --> + +<!-- end custom footer snippets --> + <div class="page__footer-follow"> + <ul class="social-icons"> + + <li><strong>Follow:</strong></li> + + + <li><a href="https://twitter.com/ApacheRocketMQ";><i class="fa fa-fw fa-twitter-square" aria-hidden="true"></i> Twitter</a></li> + + + + <li><a href="http://github.com/apache/incubator-rocketmq";><i class="fa fa-fw fa-github" aria-hidden="true"></i> GitHub</a></li> + + + <li><a href="/feed.xml"><i class="fa fa-fw fa-rss-square" aria-hidden="true"></i> Feed</a></li> + </ul> +</div> + +<div class="page__footer-copyright">Copyright © 2017 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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Generally speaking, we are deploying a resilient RocketMQ cluster having no single point of failure.</p> + +<h1 id="name-server">Name Server</h1> + +<p>To ensure the cluster can still operate normally when name server instance crashes, two or more name server instances are recommended. As long as there is one name server instance alive, the whole cluster remains serving.</p> + +<p>Name server follows share-nothing design paradigm. Brokers send heartbeat data to all name servers. Producers and consumers may query meta data from any one of name servers available while sending / consuming messages.</p> + +<h1 id="broker">Broker</h1> + +<p>Brokers can be divided into two categories according to their roles: master and slave. Master brokers can read and write while slave brokers can only read messages replicated from master. Master brokers have brokerId=0; brokerId of slave is non-zero.</p> + +<p>Brokers may also be grouped by the brokerName property. Slave brokers find their master through brokerName. One master broker along with zero, one or multiple slave brokers is called a broker set.</p> + +<p>In serious scenarios, we should have at least two broker sets. Each topic, as you guess, resides in two or more broker sets.</p> + +<h1 id="disk-flush-type-sync_flush--async_flush">Disk Flush Type: SYNC_FLUSH / ASYNC_FLUSH</h1> + +<p>Each broker can be configured to be sync or async in terms of IO flushing strategy. To put it simply, if your business tolerates none message loss at extreme scenarios like OS crash or power loss, SYNC_FLUSH mode is recommended. Broker of SYNC_FLUSH mode would flush each message it receives onto disk before acknowledging producer. Obviously, throughout of this mode is highly dependent on IOPS of your hard disk.</p> + +<p>Broker of ASYNC_FLUSH mode, on the other hand, takes advantage of group-committing: only flushes dirty page caches to disk periodically or when count of dirty page caches reaches certain amount. Hence, the latter yields better performance.</p> + +<h1 id="replication-sync--async-broker">Replication: Sync / Async Broker</h1> + +<p>Similar to many replication system, sync brokers await until commit log is replicated to a slave before acknowledging. Async brokers, instead, return immediately after messages are processed on master.</p> + +<h1 id="configuration">Configuration</h1> + +<p>There are three pre-built configurations shipped with the distribution of RocketMQ under conf folder for your reference:</p> + +<ol> + <li>2m-2s-sync</li> + <li>2m-2s-async</li> + <li>2m-noslave</li> +</ol> + +<p>Note: all configurations uses ASYNC_FLUSH.</p> + +<h1 id="deployment-example">Deployment Example</h1> + +<p>For example, We want to have a cluster with 2 name servers, 2 broker sets with general purpose: +for this example, we choose <code class="highlighter-rouge">2m-2s-sync</code> +Assuming binary RocketMQ is at <code class="highlighter-rouge">/home/rocketmq/dist</code></p> + +<ol> + <li> + <p>Start up two name servers as is shown in Quick Start guide. Assume their IPs are 192.168.0.2 and 192.168.0.3.</p> + </li> + <li> + <p>Start brokers</p> + + <p><code class="highlighter-rouge">cd /home/rocketmq/dist/bin</code></p> + + <p><code class="highlighter-rouge">bash mqbroker -c ../conf/2m-2s-sync/broker-a.properties -n 192.168.0.2:9876,192.168.0.3:9876</code></p> + + <p><code class="highlighter-rouge">bash mqbroker -c ../conf/2m-2s-sync/broker-a-s.properties -n 192.168.0.2:9876,192.168.0.3:9876</code></p> + + <p><code class="highlighter-rouge">bash mqbroker -c ../conf/2m-2s-sync/broker-b.properties -n 192.168.0.2:9876,192.168.0.3:9876</code></p> + + <p><code class="highlighter-rouge">bash mqbroker -c ../conf/2m-2s-sync/broker-b-s.properties -n 192.168.0.2:9876,192.168.0.3:9876</code></p> + </li> + <li> + <p>Verify</p> + + <p>Execute the following command to verify</p> + + <p><code class="highlighter-rouge">bash mqadmin clusterList</code></p> + </li> +</ol> + + + </section> + + <footer class="page__meta"> + + + + + + <p class="page__date"><strong><i class="fa fa-fw fa-calendar" aria-hidden="true"></i> Updated:</strong> <time datetime="2016-12-17">December 17, 2016</time></p> + + </footer> + + <section class="page__share"> + + <h4 class="page__share-title">Share on</h4> + + + <a href="https://twitter.com/intent/tweet?via=ApacheRocketMQ&text=Cluster Configuration and Deployment /docs/cluster-deployment/" class="btn btn--twitter" title="Share on Twitter"><i class="fa fa-fw fa-twitter" aria-hidden="true"></i><span> Twitter</span></a> + + <a href="https://www.facebook.com/sharer/sharer.php?u=/docs/cluster-deployment/"; class="btn btn--facebook" title="Share on Facebook"><i class="fa fa-fw fa-facebook" aria-hidden="true"></i><span> Facebook</span></a> + + <a href="https://plus.google.com/share?url=/docs/cluster-deployment/"; class="btn btn--google-plus" title="Share on Google Plus"><i class="fa fa-fw fa-google-plus" aria-hidden="true"></i><span> Google+</span></a> + + <a href="https://www.linkedin.com/shareArticle?mini=true&url=/docs/cluster-deployment/"; class="btn btn--linkedin" title="Share on LinkedIn"><i class="fa fa-fw fa-linkedin" aria-hidden="true"></i><span> LinkedIn</span></a> +</section> + + + + <nav class="pagination"> + + <a href="/docs/cli-admin-tool/" class="pagination--pager" title="CLI Admin Tool +">Previous</a> + + + <a href="/docs/pull-request/" class="pagination--pager" title="Best Practice in Pull Request +">Next</a> + + </nav> + + </div> + + + <div class="page__comments"> + + + <h4 class="page__comments-title">Leave a Comment</h4> + <section id="disqus_thread"></section> + +</div> + + </article> + + + +</div> + + <div class="page__footer"> + <footer> + <!-- start custom footer snippets --> + +<!-- end custom footer snippets --> + <div class="page__footer-follow"> + <ul class="social-icons"> + + <li><strong>Follow:</strong></li> + + + <li><a href="https://twitter.com/ApacheRocketMQ";><i class="fa fa-fw fa-twitter-square" aria-hidden="true"></i> Twitter</a></li> + + + + <li><a href="http://github.com/apache/incubator-rocketmq";><i class="fa fa-fw fa-github" aria-hidden="true"></i> GitHub</a></li> + + + <li><a href="/feed.xml"><i class="fa fa-fw fa-rss-square" aria-hidden="true"></i> Feed</a></li> + </ul> +</div> + +<div class="page__footer-copyright">Copyright © 2017 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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RocketMQ provides multiple paradigms of sending: synchronous, asynchronous and one-way.</p> + +<h2 id="producer-group">Producer Group</h2> + +<p>Producers of the same role are grouped together. A different producer instance of the same producer group may be contacted by a broker to commit or roll back a transaction in case the original producer crashed after starting the transaction.</p> + +<p><strong>Warning</strong>: Considering the provided producer is sufficiently powerful at sending messages, only one instance is allowed per producer group and process to avoid unnecessarily initializing of producer instances.</p> + +<h1 id="consumer">Consumer</h1> + +<p>A Consumer pulls messages from brokers and feeds them into application. In perspective of user application, two types of consumers are provided:</p> + +<h2 id="pullconsumer">PullConsumer</h2> + +<p>Pull consumer actively pulls messages from brokers. Once batches of messages are pulled, user application initiates consuming process.</p> + +<h2 id="pushconsumer">PushConsumer</h2> + +<p>Push consumer, on the other hand, encapsulates message pulling, consuming progress maintaining and other effortful work inside, leaving a callback interface to end user to implement which will be executed on message arrival.</p> + +<h2 id="consumer-group">Consumer Group</h2> + +<p>Similar to previously mentioned producer group, consumers of the exactly same role are grouped together and named <strong>Consumer Group</strong>.</p> + +<p>Consumer Group is a great concept with which achieving goals of load-balance and fault-tolerance, in terms of message consuming, is super easy.</p> + +<p><strong>Warning</strong>: consumer instances of a consumer group <strong>must</strong> have exactly same topic subscription(s).</p> + +<h1 id="topic">Topic</h1> + +<p>Topic is a category to which producers deliver messages and from which consumers pull messages. Topics have very loose relation with producers and consumers. Specifically, a topic may have zero, one or multiple producers that sends messages to it; conversely, a producer can sends messages of different topics. In consumerâs view, a topic may be subscribed by zero, one or multiple consumer groups; and a consumer group, in the same paradigm, may subscribe one or multiple topics as long as instances of this group keep their subscription consistent as emphasized in the previous section.</p> + +<h1 id="message">Message</h1> + +<p>Message is the envelope of your information to deliver. A message must be specified with a topic, which can be interpreted as address of your letter to mail to. A message may also have an optional tag set. Extra key-value pairs may also be included. For example, you may set a business key for your message and look up the message on broker server to diagnose issues during development.</p> + +<h2 id="message-queue">Message Queue</h2> + +<p>Topic, internally, is logically partitioned into one or more sub-topics. We call these sub-topics âmessage queuesâ. This concept plays a major role in implementing valuable features, including fail-over, maximum concurrency, etc.</p> + +<h2 id="tag">Tag</h2> + +<p>Tag, which can be thought as sub-topic, provides an extra flexibility for user. Through introducing tag, messages with different purposes from the same business module may have the same topic yet different tag. It would be helpful to keep your code clean and coherent.</p> + +<h2 id="broker">Broker</h2> + +<p>Broker is the major role of the RocketMQ system. It receives messages sent from producers, store them and being prepared to serve pull requests from consumers. It also stores message consuming related meta data, including consumer groups, consuming progress offsets and topic / queue info.</p> + +<h1 id="name-server">Name Server</h1> + +<p>Name server serves as the routing information provider. Producer/Consumer clients look up topics to find broker list to read from and write to.</p> + +<h1 id="message-model">Message Model</h1> + +<ul> + <li> + <p>Clustering</p> + </li> + <li> + <p>Broadcasting</p> + </li> +</ul> + +<h1 id="message-order">Message Order</h1> + +<p>When DefaultMQPushConsumer is employed, you may decide to consume messages orderly or concurrently.</p> + +<ul> + <li>Orderly</li> +</ul> + +<p>Consuming messages orderly means messages are consumed the same order they are sent by producers for each message queue. If you are dealing with scenario that global order is mandatory, make sure the topic you use has only one message queue.</p> + +<p><strong>Warn</strong>: If consuming orderly is specified, the maximum concurrency of message consuming is the number of message queues subscribed by the consumer group.</p> + +<ul> + <li>Concurrently</li> +</ul> + +<p>When consuming concurrently, maximum concurrency of message consuming is only limited by thread pool specified for each consumer client.</p> + +<p><strong>Warn</strong>: Message order is no longer guaranteed in this mode.</p> + + + + </section> + + <footer class="page__meta"> + + + + + + <p class="page__date"><strong><i class="fa fa-fw fa-calendar" aria-hidden="true"></i> Updated:</strong> <time datetime="2016-12-17">December 17, 2016</time></p> + + </footer> + + <section class="page__share"> + + <h4 class="page__share-title">Share on</h4> + + + <a href="https://twitter.com/intent/tweet?via=ApacheRocketMQ&text=Core Concept /docs/core-concept/" class="btn btn--twitter" title="Share on Twitter"><i class="fa fa-fw fa-twitter" aria-hidden="true"></i><span> Twitter</span></a> + + <a href="https://www.facebook.com/sharer/sharer.php?u=/docs/core-concept/"; class="btn btn--facebook" title="Share on Facebook"><i class="fa fa-fw fa-facebook" aria-hidden="true"></i><span> Facebook</span></a> + + <a href="https://plus.google.com/share?url=/docs/core-concept/"; class="btn btn--google-plus" title="Share on Google Plus"><i class="fa fa-fw fa-google-plus" aria-hidden="true"></i><span> Google+</span></a> + + <a href="https://www.linkedin.com/shareArticle?mini=true&url=/docs/core-concept/"; class="btn btn--linkedin" title="Share on LinkedIn"><i class="fa fa-fw fa-linkedin" aria-hidden="true"></i><span> LinkedIn</span></a> +</section> + + + + <nav class="pagination"> + + <a href="/docs/motivation/" class="pagination--pager" title="Motivation +">Previous</a> + + + <a href="/docs/cli-admin-tool/" class="pagination--pager" title="CLI Admin Tool +">Next</a> + + </nav> + + </div> + + + <div class="page__comments"> + + + <h4 class="page__comments-title">Leave a Comment</h4> + <section id="disqus_thread"></section> + +</div> + + </article> + + + +</div> + + <div class="page__footer"> + <footer> + <!-- start custom footer snippets --> + +<!-- end custom footer snippets --> + <div class="page__footer-follow"> + <ul class="social-icons"> + + <li><strong>Follow:</strong></li> + + + <li><a href="https://twitter.com/ApacheRocketMQ";><i class="fa fa-fw fa-twitter-square" aria-hidden="true"></i> Twitter</a></li> + + + + <li><a href="http://github.com/apache/incubator-rocketmq";><i class="fa fa-fw fa-github" aria-hidden="true"></i> GitHub</a></li> + + + <li><a href="/feed.xml"><i class="fa fa-fw fa-rss-square" aria-hidden="true"></i> Feed</a></li> + </ul> +</div> + +<div class="page__footer-copyright">Copyright © 2017 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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