<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Transactions API (Developer Preview) · Apache Pulsar</title><meta name="viewport" content="width=device-width, initial-scale=1.0"/><meta name="generator" content="Docusaurus"/><meta name="description" content="All messages in a transaction is available only to consumers after the transaction is committed. If a transaction is aborted, all the writes and acknowledgments in this transaction rollback. "/><meta name="docsearch:version" content="2.7.0"/><meta name="docsearch:language" content="en"/><meta property="og:title" content="Transactions API (Developer Preview) · Apache Pulsar"/><meta property="og:type" content="website"/><meta property="og:url" content="https://pulsar.apache.org/"/><meta property="og:description" content="All messages in a transaction is available only to consumers after the transaction is committed. If a transaction is aborted, all the writes and acknowledgments in this transaction rollback. "/><meta name="twitter:card" content="summary"/><meta name="twitter:image" content="https://pulsar.apache.org/img/pulsar.svg"/><link rel="shortcut icon" href="/img/pulsar.ico"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/atom-one-dark.min.css"/><link rel="alternate" type="application/atom+xml" href="https://pulsar.apache.org/blog/atom.xml" title="Apache Pulsar Blog ATOM Feed"/><link rel="alternate" type="application/rss+xml" href="https://pulsar.apache.org/blog/feed.xml" title="Apache Pulsar Blog RSS Feed"/><link rel="stylesheet" href="/css/code-blocks-buttons.css"/><script type="text/javascript" src="https://buttons.github.io/buttons.js"></script><script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.0/clipboard.min.js"></script><script type="text/javascript" src="/js/custom.js"></script><script src="/js/scrollSpy.js"></script><link rel="stylesheet" href="/css/main.css"/><script src="/js/codetabs.js"></script></head><body class="sideNavVisible separateOnPageNav"><div class="fixedHeaderContainer"><div class="headerWrapper wrapper"><header><a href="/en"><img class="logo" src="/img/pulsar.svg" alt="Apache Pulsar"/></a><a href="/en/versions"><h3>2.7.0</h3></a><div class="navigationWrapper navigationSlider"><nav class="slidingNav"><ul class="nav-site nav-site-internal"><li class="siteNavGroupActive"><a href="/docs/en/2.7.0/getting-started-standalone" target="_self">Docs</a></li><li class=""><a href="/en/download" target="_self">Download</a></li><li class="siteNavGroupActive"><a href="/docs/en/2.7.0/client-libraries" target="_self">Clients</a></li><li class=""><a href="#restapis" target="_self">REST APIs</a></li><li class=""><a href="#cli" target="_self">Cli</a></li><li class=""><a href="/blog/" target="_self">Blog</a></li><li class=""><a href="#community" target="_self">Community</a></li><li class=""><a href="#apache" target="_self">Apache</a></li><li class=""><a href="https://pulsar-next.staged.apache.org/" target="_self">New Website (Beta)</a></li><span><li><a id="languages-menu" href="#"><img class="languages-icon" src="/img/language.svg" alt="Languages icon"/>English</a><div id="languages-dropdown" class="hide"><ul id="languages-dropdown-items"><li><a href="/docs/ja/2.7.0/transactions-api">日本語</a></li><li><a href="/docs/fr/2.7.0/transactions-api">Français</a></li><li><a href="/docs/ko/2.7.0/transactions-api">한국어</a></li><li><a href="/docs/zh-CN/2.7.0/transactions-api">中文</a></li><li><a href="/docs/zh-TW/2.7.0/transactions-api">繁體中文</a></li><li><a href="https://crowdin.com/project/apache-pulsar" target="_blank" rel="noreferrer noopener">Help Translate</a></li></ul></div></li><script>
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<p>Currently, Pulsar transaction is a developer preview feature. It is disabled by default. You can enable the feature and use transactions in your application in development environment.</p>
<h2><a class="anchor" aria-hidden="true" id="prerequisites"></a><a href="#prerequisites" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Prerequisites</h2>
<ol>
<li>To enable transactions in Pulsar, you need to configure the parameter in the <code>broker.conf</code> file.</li>
</ol>
<pre><code class="hljs"><span class="hljs-attr">transactionCoordinatorEnabled</span>=<span class="hljs-literal">true</span>
</code></pre>
<ol start="2">
<li>Initialize transaction coordinator metadata, so the transaction coordinators can leverage advantages of the partitioned topic, such as load balance.</li>
</ol>
<pre><code class="hljs">bin/pulsar initialize-transaction-coordinator-metadata -cs <span class="hljs-number">127.0</span><span class="hljs-number">.0</span><span class="hljs-number">.1</span>:<span class="hljs-number">2181</span> -c standalone
</code></pre>
<p>After initializing transaction coordinator metadata, you can use the transactions API. The following APIs are available.</p>
<h2><a class="anchor" aria-hidden="true" id="initialize-pulsar-client"></a><a href="#initialize-pulsar-client" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Initialize Pulsar client</h2>
<p>You can enable transaction for transaction client and initialize transaction coordinator client.</p>
<pre><code class="hljs">PulsarClient pulsarClient = <span class="hljs-module-access"><span class="hljs-module"><span class="hljs-identifier">PulsarClient</span>.</span></span>builder<span class="hljs-literal">()</span>
        .service<span class="hljs-constructor">Url(<span class="hljs-string">"pulsar://localhost:6650"</span>)</span>
        .enable<span class="hljs-constructor">Transaction(<span class="hljs-params">true</span>)</span>
        .build<span class="hljs-literal">()</span>;
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="start-transactions"></a><a href="#start-transactions" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Start transactions</h2>
<p>You can start transaction in the following way.</p>
<pre><code class="hljs">Transaction txn = pulsarClient
        <span class="hljs-string">.newTransaction</span><span class="hljs-params">()</span>
        <span class="hljs-string">.withTransactionTimeout</span><span class="hljs-params">(5, TimeUnit.MINUTES)</span>
        <span class="hljs-string">.build</span><span class="hljs-params">()</span>
        <span class="hljs-string">.get</span><span class="hljs-params">()</span>;
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="produce-transaction-messages"></a><a href="#produce-transaction-messages" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Produce transaction messages</h2>
<p>A transaction parameter is required when producing new transaction messages. The semantic of the transaction messages in Pulsar is <code>read-committed</code>, so the consumer cannot receive the ongoing transaction messages before the transaction is committed.</p>
<pre><code class="hljs">producer.<span class="hljs-keyword">new</span><span class="hljs-constructor">Message(<span class="hljs-params">txn</span>)</span>.value(<span class="hljs-string">"Hello Pulsar Transaction"</span>.get<span class="hljs-constructor">Bytes()</span>).send<span class="hljs-constructor">Async()</span>;
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="acknowledge-the-messages-with-the-transaction"></a><a href="#acknowledge-the-messages-with-the-transaction" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Acknowledge the messages with the transaction</h2>
<p>The transaction acknowledgement requires a transaction parameter. The transaction acknowledgement marks the messages state to pending-ack state. When the transaction is committed, the pending-ack state becomes ack state. If the transaction is aborted, the pending-ack state becomes unack state.</p>
<pre><code class="hljs"><span class="hljs-keyword">Message</span>&lt;byte[]&gt; <span class="hljs-keyword">message</span> = consumer.receive();
consumer.acknowledgeAsync(<span class="hljs-keyword">message</span>.getMessageId(), txn);
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="commit-transactions"></a><a href="#commit-transactions" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Commit transactions</h2>
<p>When the transaction is committed, consumers receive the transaction messages and the pending-ack state becomes ack state.</p>
<pre><code class="hljs"><span class="hljs-selector-tag">txn</span><span class="hljs-selector-class">.commit</span>()<span class="hljs-selector-class">.get</span>();
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="abort-transaction"></a><a href="#abort-transaction" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Abort transaction</h2>
<p>When the transaction is aborted, the transaction acknowledgement is canceled and the pending-ack messages are redelivered.</p>
<pre><code class="hljs">txn.<span class="hljs-built_in">abort</span>().<span class="hljs-built_in">get</span>();
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="example"></a><a href="#example" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example</h3>
<p>The following example shows how messages are processed in transaction.</p>
<pre><code class="hljs">PulsarClient pulsarClient = <span class="hljs-module-access"><span class="hljs-module"><span class="hljs-identifier">PulsarClient</span>.</span></span>builder<span class="hljs-literal">()</span>
        .service<span class="hljs-constructor">Url(<span class="hljs-params">getPulsarServiceList</span>()</span>.get(<span class="hljs-number">0</span>).get<span class="hljs-constructor">BrokerServiceUrl()</span>)
        .stats<span class="hljs-constructor">Interval(0, TimeUnit.SECONDS)</span>
        .enable<span class="hljs-constructor">Transaction(<span class="hljs-params">true</span>)</span>
        .build<span class="hljs-literal">()</span>;

String sourceTopic = <span class="hljs-string">"public/default/source-topic"</span>;
String sinkTopic = <span class="hljs-string">"public/default/sink-topic"</span>;

Producer&lt;String&gt; sourceProducer = pulsarClient
        .<span class="hljs-keyword">new</span><span class="hljs-constructor">Producer(Schema.STRING)</span>
        .topic(sourceTopic)
        .create<span class="hljs-literal">()</span>;
sourceProducer.<span class="hljs-keyword">new</span><span class="hljs-constructor">Message()</span>.value(<span class="hljs-string">"hello pulsar transaction"</span>).send<span class="hljs-constructor">Async()</span>;

Consumer&lt;String&gt; sourceConsumer = pulsarClient
        .<span class="hljs-keyword">new</span><span class="hljs-constructor">Consumer(Schema.STRING)</span>
        .topic(sourceTopic)
        .subscription<span class="hljs-constructor">Name(<span class="hljs-string">"test"</span>)</span>
        .subscription<span class="hljs-constructor">Type(SubscriptionType.Shared)</span>
        .subscription<span class="hljs-constructor">InitialPosition(SubscriptionInitialPosition.Earliest)</span>
        .subscribe<span class="hljs-literal">()</span>;

Producer&lt;String&gt; sinkProducer = pulsarClient
        .<span class="hljs-keyword">new</span><span class="hljs-constructor">Producer(Schema.STRING)</span>
        .topic(sinkTopic)
        .send<span class="hljs-constructor">Timeout(0, TimeUnit.MILLISECONDS)</span>
        .create<span class="hljs-literal">()</span>;

Transaction txn = pulsarClient
        .<span class="hljs-keyword">new</span><span class="hljs-constructor">Transaction()</span>
        .<span class="hljs-keyword">with</span><span class="hljs-constructor">TransactionTimeout(5, TimeUnit.MINUTES)</span>
        .build<span class="hljs-literal">()</span>
        .get<span class="hljs-literal">()</span>;

<span class="hljs-comment">// source message acknowledgement and sink message produce belong to one transaction,</span>
<span class="hljs-comment">// they are combined into an atomic operation.</span>
Message&lt;String&gt; message = sourceConsumer.receive<span class="hljs-literal">()</span>;
sourceConsumer.acknowledge<span class="hljs-constructor">Async(<span class="hljs-params">message</span>.<span class="hljs-params">getMessageId</span>()</span>, txn);
sinkProducer.<span class="hljs-keyword">new</span><span class="hljs-constructor">Message(<span class="hljs-params">txn</span>)</span>.value(<span class="hljs-string">"sink data"</span>).send<span class="hljs-constructor">Async()</span>;

txn.commit<span class="hljs-literal">()</span>.get<span class="hljs-literal">()</span>;
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="enable-batch-messages-in-transactions"></a><a href="#enable-batch-messages-in-transactions" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Enable batch messages in transactions</h2>
<p>To enable batch messages in transactions, you need to enable the batch index acknowledgement feature. The transaction acks check whether the batch index acknowledgement conflicts.</p>
<p>To enable batch index acknowledgement, you need to set <code>acknowledgmentAtBatchIndexLevelEnabled</code> to <code>true</code> in the <code>broker.conf</code> or <code>standalone.conf</code> file.</p>
<pre><code class="hljs"><span class="hljs-attr">acknowledgmentAtBatchIndexLevelEnabled</span>=<span class="hljs-literal">true</span>
</code></pre>
<p>And then you need to call the <code>enableBatchIndexAcknowledgment(true)</code> method in the consumer builder.</p>
<pre><code class="hljs">Consumer&lt;byte[]&gt; sinkConsumer = pulsarClient
        <span class="hljs-string">.newConsumer</span><span class="hljs-params">()</span>
        <span class="hljs-string">.topic</span><span class="hljs-params">(transferTopic)</span>
        <span class="hljs-string">.subscriptionName</span><span class="hljs-params">("sink-topic")</span>
        <span class="hljs-string">.subscriptionInitialPosition</span><span class="hljs-params">(SubscriptionInitialPosition.Earliest)</span>
        <span class="hljs-string">.subscriptionType</span><span class="hljs-params">(SubscriptionType.Shared)</span>
        <span class="hljs-string">.enableBatchIndexAcknowledgment</span><span class="hljs-params">(true)</span> <span class="hljs-string">//</span> enable <span class="hljs-keyword">batch</span> index acknowledgement
        <span class="hljs-string">.subscribe</span><span class="hljs-params">()</span>;
</code></pre>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/en/2.7.0/transactions-guarantee"><span class="arrow-prev">← </span><span>Transactions Guarantee</span></a><a class="docs-next button" href="/docs/en/2.7.0/helm-overview"><span>Overview</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#prerequisites">Prerequisites</a></li><li><a href="#initialize-pulsar-client">Initialize Pulsar client</a></li><li><a href="#start-transactions">Start transactions</a></li><li><a href="#produce-transaction-messages">Produce transaction messages</a></li><li><a href="#acknowledge-the-messages-with-the-transaction">Acknowledge the messages with the transaction</a></li><li><a href="#commit-transactions">Commit transactions</a></li><li><a href="#abort-transaction">Abort transaction</a><ul class="toc-headings"><li><a href="#example">Example</a></li></ul></li><li><a href="#enable-batch-messages-in-transactions">Enable batch messages in transactions</a></li></ul></nav></div><footer class="nav-footer" id="footer"><section class="copyright">Copyright © 2022 The Apache Software Foundation. All Rights Reserved. Apache, Apache Pulsar and the Apache feather logo are trademarks of The Apache Software Foundation.</section><span><script>
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