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<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Understand schema · Apache Pulsar</title><meta name="viewport" content="width=device-width, initial-scale=1.0"/><meta name="generator" content="Docusaurus"/><meta name="description" content="This chapter explains the basic concepts of Pulsar schema, focuses on the topics of particular importance, and provides additional background."/><meta name="docsearch:version" content="2.5.1"/><meta name="docsearch:language" content="en"/><meta property="og:title" content="Understand schema · Apache Pulsar"/><meta property="og:type" content="website"/><meta property="og:url" content="https://pulsar.apache.org/"/><meta property="og:description" content="This chapter explains the basic concepts of Pulsar schema, focuses on the topics of particular importance, and provides additional background."/><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>2.5.1</h3></a><div class="navigationWrapper navigationSlider"><nav class="slidingNav"><ul class="nav-site nav-site-internal"><li class="siteNavGroupActive"><a href="/docs/en/2.5.1/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/2.5.1/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/2.5.1/schema-understand">日本語</a></li><li><a href="/docs/fr/2.5.1/schema-understand">Français</a></li><li><a href="/docs/ko/2.5.1/schema-understand">한국어</a></li><li><a href="/docs/zh-CN/2.5.1/schema-understand">中文</a></li><li><a href="/docs/zh-TW/2.5.1/schema-understand">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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<h2><a class="anchor" aria-hidden="true" id="schemainfo"></a><a href="#schemainfo" 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>SchemaInfo</h2>
<p>Pulsar schema is defined in a data structure called <code>SchemaInfo</code>.</p>
<p>The <code>SchemaInfo</code> is stored and enforced on a per-topic basis and cannot be stored at the namespace or tenant level.</p>
<p>A <code>SchemaInfo</code> consists of the following fields:</p>
<table style="table">
<tr>
<th>
<p>Field</p>
</th>
<th>
<p>Description</p>
</th>
</tr>
<tr>
<td>
<p><code>name</code></p>
</td>
<td>
<p>Schema name (a string).</p>
</td>
</tr>
<tr>
<td>
<p><code>type</code></p>
</td>
<td>
<p>Schema type, which determines how to interpret the schema data.</p>
<ul>
<li><p>Predefined schema: see <a href="/docs/en/2.5.1/schema-understand#schema-type">here</a>.</p></li>
<li><p>Customized schema: it is left as an empty string.</p></li>
</ul>
</td>
</tr>
<tr>
<td>
<p><code>schema</code>（<code>payload</code>)</p>
</td>
<td>
<p>Schema data, which is a sequence of 8-bit unsigned bytes and schema-type specific.</p>
</td>
</tr>
<tr>
<td>
<p><code>properties</code></p>
</td>
<td>
<p>It is a user defined properties as a string/string map.</p>
<p>Applications can use this bag for carrying any application specific logics.</p>
<p>Possible properties might be the Git hash associated with the schema, an environment string like <code>dev</code> or <code>prod</code>.</p>
</td>
</tr>
</table>
<p><strong>Example</strong></p>
<p>This is the <code>SchemaInfo</code> of a string.</p>
<pre><code class="hljs css language-json">{
<span class="hljs-attr">"name"</span>: <span class="hljs-string">"test-string-schema"</span>,
<span class="hljs-attr">"type"</span>: <span class="hljs-string">"STRING"</span>,
<span class="hljs-attr">"schema"</span>: <span class="hljs-string">""</span>,
<span class="hljs-attr">"properties"</span>: {}
}
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="schema-type"></a><a href="#schema-type" 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>Schema type</h2>
<p>Pulsar supports various schema types, which are mainly divided into two categories:</p>
<ul>
<li><p>Primitive type</p></li>
<li><p>Complex type</p></li>
</ul>
<h3><a class="anchor" aria-hidden="true" id="primitive-type"></a><a href="#primitive-type" 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>Primitive type</h3>
<p>Currently, Pulsar supports the following primitive types:</p>
<table>
<thead>
<tr><th>Primitive Type</th><th>Description</th></tr>
</thead>
<tbody>
<tr><td><code>BOOLEAN</code></td><td>A binary value</td></tr>
<tr><td><code>INT8</code></td><td>A 8-bit signed integer</td></tr>
<tr><td><code>INT16</code></td><td>A 16-bit signed integer</td></tr>
<tr><td><code>INT32</code></td><td>A 32-bit signed integer</td></tr>
<tr><td><code>INT64</code></td><td>A 64-bit signed integer</td></tr>
<tr><td><code>FLOAT</code></td><td>A single precision (32-bit) IEEE 754 floating-point number</td></tr>
<tr><td><code>DOUBLE</code></td><td>A double-precision (64-bit) IEEE 754 floating-point number</td></tr>
<tr><td><code>BYTES</code></td><td>A sequence of 8-bit unsigned bytes</td></tr>
<tr><td><code>STRING</code></td><td>A Unicode character sequence</td></tr>
<tr><td><code>TIMESTAMP</code> (<code>DATE</code>, <code>TIME</code>)</td><td>A logic type represents a specific instant in time with millisecond precision. <br>It stores the number of milliseconds since <code>January 1, 1970, 00:00:00 GMT</code> as an <code>INT64</code> value</td></tr>
</tbody>
</table>
<p>For primitive types, Pulsar does not store any schema data in <code>SchemaInfo</code>. The <code>type</code> in <code>SchemaInfo</code> is used to determine how to serialize and deserialize the data.</p>
<p>Some of the primitive schema implementations can use <code>properties</code> to store implementation-specific tunable settings. For example, a <code>string</code> schema can use <code>properties</code> to store the encoding charset to serialize and deserialize strings.</p>
<p>The conversions between <strong>Pulsar schema types</strong> and <strong>language-specific primitive types</strong> are as below.</p>
<table>
<thead>
<tr><th>Schema Type</th><th>Java Type</th><th>Python Type</th><th>Go Type</th></tr>
</thead>
<tbody>
<tr><td>BOOLEAN</td><td>boolean</td><td>bool</td><td>bool</td></tr>
<tr><td>INT8</td><td>byte</td><td></td><td>int8</td></tr>
<tr><td>INT16</td><td>short</td><td></td><td>int16</td></tr>
<tr><td>INT32</td><td>int</td><td></td><td>int32</td></tr>
<tr><td>INT64</td><td>long</td><td></td><td>int64</td></tr>
<tr><td>FLOAT</td><td>float</td><td>float</td><td>float32</td></tr>
<tr><td>DOUBLE</td><td>double</td><td>float</td><td>float64</td></tr>
<tr><td>BYTES</td><td>byte[], ByteBuffer, ByteBuf</td><td>bytes</td><td>[]byte</td></tr>
<tr><td>STRING</td><td>string</td><td>str</td><td>string</td></tr>
<tr><td>TIMESTAMP</td><td>java.sql.Timestamp</td><td></td><td></td></tr>
<tr><td>TIME</td><td>java.sql.Time</td><td></td><td></td></tr>
<tr><td>DATE</td><td>java.util.Date</td><td></td><td></td></tr>
</tbody>
</table>
<p><strong>Example</strong></p>
<p>This example demonstrates how to use a string schema.</p>
<ol>
<li><p>Create a producer with a string schema and send messages.</p>
<pre><code class="hljs css language-java">Producer&lt;String&gt; producer = client.newProducer(Schema.STRING).create();
producer.newMessage().value(<span class="hljs-string">"Hello Pulsar!"</span>).send();
</code></pre></li>
<li><p>Create a consumer with a string schema and receive messages.</p>
<pre><code class="hljs css language-java">Consumer&lt;String&gt; consumer = client.newConsumer(Schema.STRING).subscribe();
consumer.receive();
</code></pre></li>
</ol>
<h3><a class="anchor" aria-hidden="true" id="complex-type"></a><a href="#complex-type" 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>Complex type</h3>
<p>Currently, Pulsar supports the following complex types:</p>
<table>
<thead>
<tr><th>Complex Type</th><th>Description</th></tr>
</thead>
<tbody>
<tr><td><code>keyvalue</code></td><td>Represents a complex type of a key/value pair.</td></tr>
<tr><td><code>struct</code></td><td>Supports <strong>AVRO</strong>, <strong>JSON</strong>, and <strong>Protobuf</strong>.</td></tr>
</tbody>
</table>
<h4><a class="anchor" aria-hidden="true" id="keyvalue"></a><a href="#keyvalue" 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>keyvalue</h4>
<p><code>Keyvalue</code> schema helps applications define schemas for both key and value.</p>
<p>For <code>SchemaInfo</code> of <code>keyvalue</code> schema, Pulsar stores the <code>SchemaInfo</code> of key schema and the <code>SchemaInfo</code> of value schema together.</p>
<p>Pulsar provides two methods to encode a key/value pair in messages：</p>
<ul>
<li><p><code>INLINE</code></p></li>
<li><p><code>SEPARATED</code></p></li>
</ul>
<p>Users can choose the encoding type when constructing the key/value schema.</p>
<h5><a class="anchor" aria-hidden="true" id="inline"></a><a href="#inline" 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>INLINE</h5>
<p>Key/value pairs will be encoded together in the message payload.</p>
<h5><a class="anchor" aria-hidden="true" id="separated"></a><a href="#separated" 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>SEPARATED</h5>
<p>Key will be encoded in the message key and the value will be encoded in the message payload.</p>
<p><strong>Example</strong></p>
<p>This example shows how to construct a key/value schema and then use it to produce and consume messages.</p>
<ol>
<li><p>Construct a key/value schema with <code>INLINE</code> encoding type.</p>
<pre><code class="hljs css language-java">Schema&lt;KeyValue&lt;Integer, String&gt;&gt; kvSchema = Schema.KeyValue(
Schema.INT32,
Schema.STRING,
KeyValueEncodingType.INLINE
);
</code></pre></li>
<li><p>Optionally, construct a key/value schema with <code>SEPARATED</code> encoding type.</p>
<pre><code class="hljs css language-java">Schema&lt;KeyValue&lt;Integer, String&gt;&gt; kvSchema = Schema.KeyValue(
Schema.INT32,
Schema.STRING,
KeyValueEncodingType.SEPARATED
);
</code></pre></li>
<li><p>Produce messages using a key/value schema.</p>
<pre><code class="hljs css language-java">Schema&lt;KeyValue&lt;Integer, String&gt;&gt; kvSchema = Schema.KeyValue(
Schema.INT32,
Schema.STRING,
KeyValueEncodingType.SEPARATED
);
Producer&lt;KeyValue&lt;Integer, String&gt;&gt; producer = client.newProducer(kvSchema)
.topic(TOPIC)
.create();
<span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> key = <span class="hljs-number">100</span>;
<span class="hljs-keyword">final</span> String value = <span class="hljs-string">"value-100"</span>;
<span class="hljs-comment">// send the key/value message</span>
producer.newMessage()
.value(<span class="hljs-keyword">new</span> KeyValue&lt;&gt;(key, value))
.send();
</code></pre></li>
<li><p>Consume messages using a key/value schema.</p>
<pre><code class="hljs css language-java">Schema&lt;KeyValue&lt;Integer, String&gt;&gt; kvSchema = Schema.KeyValue(
Schema.INT32,
Schema.STRING,
KeyValueEncodingType.SEPARATED
);
Consumer&lt;KeyValue&lt;Integer, String&gt;&gt; consumer = client.newConsumer(kvSchema)
...
.topic(TOPIC)
.subscriptionName(SubscriptionName).subscribe();
<span class="hljs-comment">// receive key/value pair</span>
Message&lt;KeyValue&lt;Integer, String&gt;&gt; msg = consumer.receive();
KeyValue&lt;Integer, String&gt; kv = msg.getValue();
</code></pre></li>
</ol>
<h4><a class="anchor" aria-hidden="true" id="struct"></a><a href="#struct" 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>struct</h4>
<p>Pulsar uses <a href="http://avro.apache.org/docs/current/spec.html">Avro Specification</a> to declare the schema definition for <code>struct</code> schema.</p>
<p>This allows Pulsar:</p>
<ul>
<li><p>to use same tools to manage schema definitions</p></li>
<li><p>to use different serialization/deserialization methods to handle data</p></li>
</ul>
<p>There are two methods to use <code>struct</code> schema：</p>
<ul>
<li><p><code>static</code></p></li>
<li><p><code>generic</code></p></li>
</ul>
<h5><a class="anchor" aria-hidden="true" id="static"></a><a href="#static" 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>static</h5>
<p>You can predefine the <code>struct</code> schema, and it can be a POJO in Java, a <code>struct</code> in Go, or classes generated by Avro or Protobuf tools.</p>
<p><strong>Example</strong></p>
<p>Pulsar gets the schema definition from the predefined <code>struct</code> using an Avro library. The schema definition is the schema data stored as a part of the <code>SchemaInfo</code>.</p>
<ol>
<li><p>Create the <em>User</em> class to define the messages sent to Pulsar topics.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">User</span> </span>{
String name;
<span class="hljs-keyword">int</span> age;
}
</code></pre></li>
<li><p>Create a producer with a <code>struct</code> schema and send messages.</p>
<pre><code class="hljs css language-java">Producer&lt;User&gt; producer = client.newProducer(Schema.AVRO(User<span class="hljs-class">.<span class="hljs-keyword">class</span>)).<span class="hljs-title">create</span>()</span>;
producer.newMessage().value(User.builder().userName(<span class="hljs-string">"pulsar-user"</span>).userId(<span class="hljs-number">1L</span>).build()).send();
</code></pre></li>
<li><p>Create a consumer with a <code>struct</code> schema and receive messages</p>
<pre><code class="hljs css language-java">Consumer&lt;User&gt; consumer = client.newConsumer(Schema.AVRO(User<span class="hljs-class">.<span class="hljs-keyword">class</span>)).<span class="hljs-title">subscribe</span>()</span>;
User user = consumer.receive();
</code></pre></li>
</ol>
<h5><a class="anchor" aria-hidden="true" id="generic"></a><a href="#generic" 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>generic</h5>
<p>Sometimes applications do not have pre-defined structs, and you can use this method to define schema and access data.</p>
<p>You can define the <code>struct</code> schema using the <code>GenericSchemaBuilder</code>, generate a generic struct using <code>GenericRecordBuilder</code> and consume messages into <code>GenericRecord</code>.</p>
<p><strong>Example</strong></p>
<ol>
<li><p>Use <code>RecordSchemaBuilder</code> to build a schema.</p>
<pre><code class="hljs css language-java">RecordSchemaBuilder recordSchemaBuilder = SchemaBuilder.record(<span class="hljs-string">"schemaName"</span>);
recordSchemaBuilder.field(<span class="hljs-string">"intField"</span>).type(SchemaType.INT32);
SchemaInfo schemaInfo = recordSchemaBuilder.build(SchemaType.AVRO);
Producer&lt;GenericRecord&gt; producer = client.newProducer(Schema.generic(schemaInfo)).create();
</code></pre></li>
<li><p>Use <code>RecordBuilder</code> to build the struct records.</p>
<pre><code class="hljs css language-java">producer.newMessage().value(schema.newRecordBuilder()
.set(<span class="hljs-string">"intField"</span>, <span class="hljs-number">32</span>)
.build()).send();
</code></pre></li>
</ol>
<h3><a class="anchor" aria-hidden="true" id="auto-schema"></a><a href="#auto-schema" 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>Auto Schema</h3>
<p>If you don't know the schema type of a Pulsar topic in advance, you can use AUTO schema to produce or consume generic records to or from brokers.</p>
<table>
<thead>
<tr><th>Auto Schema Type</th><th>Description</th></tr>
</thead>
<tbody>
<tr><td><code>AUTO_PRODUCE</code></td><td>This is useful for transferring data <strong>from a producer to a Pulsar topic that has a schema</strong>.</td></tr>
<tr><td><code>AUTO_CONSUME</code></td><td>This is useful for transferring data <strong>from a Pulsar topic that has a schema to a consumer</strong>.</td></tr>
</tbody>
</table>
<h4><a class="anchor" aria-hidden="true" id="auto_produce"></a><a href="#auto_produce" 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>AUTO_PRODUCE</h4>
<p><code>AUTO_PRODUCE</code> schema helps a producer validate whether the bytes sent by the producer is compatible with the schema of a topic.</p>
<p><strong>Example</strong></p>
<p>Suppose that:</p>
<ul>
<li><p>You have a producer processing messages from a Kafka topic <em>K</em>.</p></li>
<li><p>You have a Pulsar topic <em>P</em>, and you do not know its schema type.</p></li>
<li><p>Your application reads the messages from <em>K</em> and writes the messages to <em>P</em>.</p></li>
</ul>
<p>In this case, you can use <code>AUTO_PRODUCE</code> to verify whether the bytes produced by <em>K</em> can be sent to <em>P</em> or not.</p>
<pre><code class="hljs css language-java">Produce&lt;<span class="hljs-keyword">byte</span>[]&gt; pulsarProducer = client.newProducer(Schema.AUTO_PRODUCE())
…
.create();
<span class="hljs-keyword">byte</span>[] kafkaMessageBytes = … ;
pulsarProducer.produce(kafkaMessageBytes);
</code></pre>
<h4><a class="anchor" aria-hidden="true" id="auto_consume"></a><a href="#auto_consume" 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>AUTO_CONSUME</h4>
<p><code>AUTO_CONSUME</code> schema helps a Pulsar topic validate whether the bytes sent by a Pulsar topic is compatible with a consumer, that is, the Pulsar topic deserializes messages into language-specific objects using the <code>SchemaInfo</code> retrieved from broker-side.</p>
<p>Currently, <code>AUTO_CONSUME</code> only supports <strong>AVRO</strong> and <strong>JSON</strong> schemas. It deserializes messages into <code>GenericRecord</code>.</p>
<p><strong>Example</strong></p>
<p>Suppose that:</p>
<ul>
<li><p>You have a Pulsar topic <em>P</em>.</p></li>
<li><p>You have a consumer (for example, MySQL) receiving messages from the topic <em>P</em>.</p></li>
<li><p>You application reads the messages from <em>P</em> and writes the messages to MySQL.</p></li>
</ul>
<p>In this case, you can use <code>AUTO_CONSUME</code> to verify whether the bytes produced by <em>P</em> can be sent to MySQL or not.</p>
<pre><code class="hljs css language-java">Consumer&lt;GenericRecord&gt; pulsarConsumer = client.newConsumer(Schema.AUTO_CONSUME())
…
.subscribe();
Message&lt;GenericRecord&gt; msg = consumer.receive() ;
GenericRecord record = msg.getValue();
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="schema-version"></a><a href="#schema-version" 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>Schema version</h2>
<p>Each <code>SchemaInfo</code> stored with a topic has a version. Schema version manages schema changes happening within a topic.</p>
<p>Messages produced with a given <code>SchemaInfo</code> is tagged with a schema version, so when a message is consumed by a Pulsar client, the Pulsar client can use the schema version to retrieve the corresponding <code>SchemaInfo</code> and then use the <code>SchemaInfo</code> to deserialize data.</p>
<p>Schemas are versioned in succession. Schema storage happens in a broker that handles the associated topics so that version assignments can be made.</p>
<p>Once a version is assigned/fetched to/for a schema, all subsequent messages produced by that producer are tagged with the appropriate version.</p>
<p><strong>Example</strong></p>
<p>The following example illustrates how the schema version works.</p>
<p>Suppose that a Pulsar <a href="/docs/en/2.5.1/client-libraries-java">Java client</a> created using the code below attempts to connect to Pulsar and begins to send messages:</p>
<pre><code class="hljs css language-java">PulsarClient client = PulsarClient.builder()
.serviceUrl("pulsar://localhost:6650")
.build();
Producer&lt;SensorReading&gt; producer = client.newProducer(JSONSchema.of(SensorReading.class))
.topic("sensor-data")
.sendTimeout(3, TimeUnit.SECONDS)
.create();
</code></pre>
<p>The table below lists the possible scenarios when this connection attempt occurs and what happens in each scenario:</p>
<table class="table">
<tr>
<th>Scenario</th>
<th>What happens</th>
</tr>
<tr>
<td>
<ul>
<li>No schema exists for the topic.</li>
</ul>
</td>
<td>
<p>(1) The producer is created using the given schema.</p>
<p>(2) Since no existing schema is compatible with the <code>SensorReading</code> schema, the schema is transmitted to the broker and stored.</p>
<p>(3) Any consumer created using the same schema or topic can consume messages from the <code>sensor-data</code> topic.</p>
</td>
</tr>
<tr>
<td>
<ul>
<li><p>A schema already exists.</p></li>
<li><p>The producer connects using the same schema that is already stored.</p></li>
</ul>
</td>
<td>
<p>(1) The schema is transmitted to the broker.</p>
<p>(2) The broker determines that the schema is compatible.</p>
<p>(3) The broker attempts to store the schema in <a href="/docs/en/2.5.1/concepts-architecture-overview#persistent-storage">BookKeeper</a> but then determines that it's already stored, so it is used to tag produced messages.</p>
</td>
<tr>
<td>
<ul>
<li><p>A schema already exists.</p></li>
<li><p>The producer connects using a new schema that is compatible.</p></li>
</ul>
</td>
<td>
<p>(1) The schema is transmitted to the broker.</p>
<p>(2) The broker determines that the schema is compatible and stores the new schema as the current version (with a new version number).</p>
</td>
</tr>
</table>
<h2><a class="anchor" aria-hidden="true" id="how-does-schema-work"></a><a href="#how-does-schema-work" 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>How does schema work</h2>
<p>Pulsar schemas are applied and enforced at the <strong>topic</strong> level (schemas cannot be applied at the namespace or tenant level).</p>
<p>Producers and consumers upload schemas to brokers, so Pulsar schemas work on the producer side and the consumer side.</p>
<h3><a class="anchor" aria-hidden="true" id="producer-side"></a><a href="#producer-side" 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>Producer side</h3>
<p>This diagram illustrates how does schema work on the Producer side.</p>
<p><img src="/docs/assets/schema-producer.png" alt="Schema works at the producer side"></p>
<ol>
<li><p>The application uses a schema instance to construct a producer instance.</p>
<p>The schema instance defines the schema for the data being produced using the producer instance.</p>
<p>Take AVRO as an example, Pulsar extract schema definition from the POJO class and construct the <code>SchemaInfo</code> that the producer needs to pass to a broker when it connects.</p></li>
<li><p>The producer connects to the broker with the <code>SchemaInfo</code> extracted from the passed-in schema instance.</p></li>
<li><p>The broker looks up the schema in the schema storage to check if it is already a registered schema.</p></li>
<li><p>If yes, the broker skips the schema validation since it is a known schema, and returns the schema version to the producer.</p></li>
<li><p>If no, the broker verifies whether a schema can be automatically created in this namespace:</p></li>
</ol>
<ul>
<li><p>If <code>isAllowAutoUpdateSchema</code> sets to <strong>true</strong>, then a schema can be created, and the broker validates the schema based on the schema compatibility check strategy defined for the topic.</p></li>
<li><p>If <code>isAllowAutoUpdateSchema</code> sets to <strong>false</strong>, then a schema can not be created, and the producer is rejected to connect to the broker.</p></li>
</ul>
<p><strong>Tip</strong>:</p>
<p><code>isAllowAutoUpdateSchema</code> can be set via <strong>Pulsar admin API</strong> or <strong>REST API.</strong></p>
<p>For how to set <code>isAllowAutoUpdateSchema</code> via Pulsar admin API, see <a href="/docs/en/2.5.1/schema-manage/#manage-autoupdate-strategy">Manage AutoUpdate Strategy</a>.</p>
<ol start="6">
<li>If the schema is allowed to be updated, then the compatible strategy check is performed.</li>
</ol>
<ul>
<li><p>If the schema is compatible, the broker stores it and returns the schema version to the producer.</p>
<p>All the messages produced by this producer are tagged with the schema version.</p></li>
<li><p>If the schema is incompatible, the broker rejects it.</p></li>
</ul>
<h3><a class="anchor" aria-hidden="true" id="consumer-side"></a><a href="#consumer-side" 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>Consumer side</h3>
<p>This diagram illustrates how does Schema work on the consumer side.</p>
<p><img src="/docs/assets/schema-consumer.png" alt="Schema works at the consumer side"></p>
<ol>
<li><p>The application uses a schema instance to construct a consumer instance.</p>
<p>The schema instance defines the schema that the consumer uses for decoding messages received from a broker.</p></li>
<li><p>The consumer connects to the broker with the <code>SchemaInfo</code> extracted from the passed-in schema instance.</p></li>
<li><p>The broker determines whether the topic has one of them (a schema/data/a local consumer and a local producer).</p></li>
<li><p>If a topic does not have all of them (a schema/data/a local consumer and a local producer):</p>
<ul>
<li><p>If <code>isAllowAutoUpdateSchema</code> sets to <strong>true</strong>, then the consumer registers a schema and it is connected to a broker.</p></li>
<li><p>If <code>isAllowAutoUpdateSchema</code> sets to <strong>false</strong>, then the consumer is rejected to connect to a broker.</p></li>
</ul></li>
<li><p>If a topic has one of them (a schema/data/a local consumer and a local producer), then the schema compatibility check is performed.</p>
<ul>
<li><p>If the schema passes the compatibility check, then the consumer is connected to the broker.</p></li>
<li><p>If the schema does not pass the compatibility check, then the consumer is rejected to connect to the broker.</p></li>
</ul></li>
<li><p>The consumer receives messages from the broker.</p>
<p>If the schema used by the consumer supports schema versioning (for example, AVRO schema), the consumer fetches the <code>SchemaInfo</code> of the version tagged in messages and uses the passed-in schema and the schema tagged in messages to decode the messages.</p></li>
</ol>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/en/2.5.1/schema-get-started"><span class="arrow-prev">← </span><span>Get started</span></a><a class="docs-next button" href="/docs/en/2.5.1/schema-evolution-compatibility"><span>Schema evolution and compatibility</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#schemainfo">SchemaInfo</a></li><li><a href="#schema-type">Schema type</a><ul class="toc-headings"><li><a href="#primitive-type">Primitive type</a></li><li><a href="#complex-type">Complex type</a></li><li><a href="#auto-schema">Auto Schema</a></li></ul></li><li><a href="#schema-version">Schema version</a></li><li><a href="#how-does-schema-work">How does schema work</a><ul class="toc-headings"><li><a href="#producer-side">Producer side</a></li><li><a href="#consumer-side">Consumer side</a></li></ul></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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