<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Materialized View · Apache Druid</title><meta name="viewport" content="width=device-width"/><link rel="canonical" href="https://druid.apache.org/docs/0.17.1/development/extensions-contrib/materialized-view.html"/><meta name="generator" content="Docusaurus"/><meta name="description" content="&lt;!--"/><meta name="docsearch:language" content="en"/><meta name="docsearch:version" content="0.17.1" /><meta property="og:title" content="Materialized View · Apache Druid"/><meta property="og:type" content="website"/><meta property="og:url" content="https://druid.apache.org/index.html"/><meta property="og:description" content="&lt;!--"/><meta property="og:image" content="https://druid.apache.org/img/druid_nav.png"/><meta name="twitter:card" content="summary"/><meta name="twitter:image" content="https://druid.apache.org/img/druid_nav.png"/><link rel="shortcut icon" href="/img/favicon.png"/><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/default.min.css"/><script async="" src="https://www.googletagmanager.com/gtag/js?id=UA-131010415-1"></script><script>
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href="/docs/0.17.1/comparisons/druid-vs-kudu.html">Apache Druid vs Kudu</a></li><li class="navListItem"><a class="navItem" href="/docs/0.17.1/comparisons/druid-vs-redshift.html">Apache Druid vs Redshift</a></li><li class="navListItem"><a class="navItem" href="/docs/0.17.1/comparisons/druid-vs-spark.html">Apache Druid vs Spark</a></li><li class="navListItem"><a class="navItem" href="/docs/0.17.1/comparisons/druid-vs-sql-on-hadoop.html">Apache Druid vs SQL-on-Hadoop</a></li><li class="navListItem"><a class="navItem" href="/docs/0.17.1/design/auth.html">Authentication and Authorization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.17.1/design/broker.html">Broker</a></li><li class="navListItem"><a class="navItem" href="/docs/0.17.1/design/coordinator.html">Coordinator Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.17.1/design/historical.html">Historical Process</a></li><li class="navListItem"><a class="navItem" 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<p>To use this Apache Druid feature, make sure to only load <code>materialized-view-selection</code> on Broker and load <code>materialized-view-maintenance</code> on Overlord. In addition, this feature currently requires a Hadoop cluster.</p>
<p>This feature enables Druid to greatly improve the query performance, especially when the query dataSource has a very large number of dimensions but the query only required several dimensions. This feature includes two parts. One is <code>materialized-view-maintenance</code>, and the other is <code>materialized-view-selection</code>.</p>
<h2><a class="anchor" aria-hidden="true" id="materialized-view-maintenance"></a><a href="#materialized-view-maintenance" 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>Materialized-view-maintenance</h2>
<p>In materialized-view-maintenance, dataSources user ingested are called &quot;base-dataSource&quot;. For each base-dataSource, we can submit <code>derivativeDataSource</code> supervisors to create and maintain other dataSources which we called  &quot;derived-dataSource&quot;. The dimensions and metrics of derived-dataSources are the subset of base-dataSource's.
The <code>derivativeDataSource</code> supervisor is used to keep the timeline of derived-dataSource consistent with base-dataSource. Each <code>derivativeDataSource</code> supervisor  is responsible for one derived-dataSource.</p>
<p>A sample derivativeDataSource supervisor spec is shown below:</p>
<pre><code class="hljs css language-json">   {
       <span class="hljs-attr">"type"</span>: <span class="hljs-string">"derivativeDataSource"</span>,
       <span class="hljs-attr">"baseDataSource"</span>: <span class="hljs-string">"wikiticker"</span>,
       <span class="hljs-attr">"dimensionsSpec"</span>: {
           <span class="hljs-attr">"dimensions"</span>: [
               <span class="hljs-string">"isUnpatrolled"</span>,
               <span class="hljs-string">"metroCode"</span>,
               <span class="hljs-string">"namespace"</span>,
               <span class="hljs-string">"page"</span>,
               <span class="hljs-string">"regionIsoCode"</span>,
               <span class="hljs-string">"regionName"</span>,
               <span class="hljs-string">"user"</span>
           ]
       },
       <span class="hljs-attr">"metricsSpec"</span>: [
           {
               <span class="hljs-attr">"name"</span>: <span class="hljs-string">"count"</span>,
               <span class="hljs-attr">"type"</span>: <span class="hljs-string">"count"</span>
           },
           {
               <span class="hljs-attr">"name"</span>: <span class="hljs-string">"added"</span>,
               <span class="hljs-attr">"type"</span>: <span class="hljs-string">"longSum"</span>,
               <span class="hljs-attr">"fieldName"</span>: <span class="hljs-string">"added"</span>
           }
       ],
       <span class="hljs-attr">"tuningConfig"</span>: {
           <span class="hljs-attr">"type"</span>: <span class="hljs-string">"hadoop"</span>
       }
   }
</code></pre>
<p><strong>Supervisor Configuration</strong></p>
<table>
<thead>
<tr><th>Field</th><th>Description</th><th>Required</th></tr>
</thead>
<tbody>
<tr><td>Type</td><td>The supervisor type. This should always be <code>derivativeDataSource</code>.</td><td>yes</td></tr>
<tr><td>baseDataSource</td><td>The name of base dataSource. This dataSource data should be already stored inside Druid, and the dataSource will be used as input data.</td><td>yes</td></tr>
<tr><td>dimensionsSpec</td><td>Specifies the dimensions of the data. These dimensions must be the subset of baseDataSource's dimensions.</td><td>yes</td></tr>
<tr><td>metricsSpec</td><td>A list of aggregators. These metrics must be the subset of baseDataSource's metrics. See <a href="/docs/0.17.1/querying/aggregations.html">aggregations</a>.</td><td>yes</td></tr>
<tr><td>tuningConfig</td><td>TuningConfig must be HadoopTuningConfig. See <a href="../../ingestion/hadoop.html#tuningconfig">Hadoop tuning config</a>.</td><td>yes</td></tr>
<tr><td>dataSource</td><td>The name of this derived dataSource.</td><td>no(default=baseDataSource-hashCode of supervisor)</td></tr>
<tr><td>hadoopDependencyCoordinates</td><td>A JSON array of Hadoop dependency coordinates that Druid will use, this property will override the default Hadoop coordinates. Once specified, Druid will look for those Hadoop dependencies from the location specified by druid.extensions.hadoopDependenciesDir</td><td>no</td></tr>
<tr><td>classpathPrefix</td><td>Classpath that will be prepended for the Peon process.</td><td>no</td></tr>
<tr><td>context</td><td>See below.</td><td>no</td></tr>
</tbody>
</table>
<p><strong>Context</strong></p>
<table>
<thead>
<tr><th>Field</th><th>Description</th><th>Required</th></tr>
</thead>
<tbody>
<tr><td>maxTaskCount</td><td>The max number of tasks the supervisor can submit simultaneously.</td><td>no(default=1)</td></tr>
</tbody>
</table>
<h2><a class="anchor" aria-hidden="true" id="materialized-view-selection"></a><a href="#materialized-view-selection" 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>Materialized-view-selection</h2>
<p>In materialized-view-selection, we implement a new query type <code>view</code>. When we request a view query, Druid will try its best to optimize the query based on query dataSource and intervals.</p>
<p>A sample view query spec is shown below:</p>
<pre><code class="hljs css language-json">   {
       <span class="hljs-attr">"queryType"</span>: <span class="hljs-string">"view"</span>,
       <span class="hljs-attr">"query"</span>: {
           <span class="hljs-attr">"queryType"</span>: <span class="hljs-string">"groupBy"</span>,
           <span class="hljs-attr">"dataSource"</span>: <span class="hljs-string">"wikiticker"</span>,
           <span class="hljs-attr">"granularity"</span>: <span class="hljs-string">"all"</span>,
           <span class="hljs-attr">"dimensions"</span>: [
               <span class="hljs-string">"user"</span>
           ],
           <span class="hljs-attr">"limitSpec"</span>: {
               <span class="hljs-attr">"type"</span>: <span class="hljs-string">"default"</span>,
               <span class="hljs-attr">"limit"</span>: <span class="hljs-number">1</span>,
               <span class="hljs-attr">"columns"</span>: [
                   {
                       <span class="hljs-attr">"dimension"</span>: <span class="hljs-string">"added"</span>,
                       <span class="hljs-attr">"direction"</span>: <span class="hljs-string">"descending"</span>,
                       <span class="hljs-attr">"dimensionOrder"</span>: <span class="hljs-string">"numeric"</span>
                   }
               ]
           },
           <span class="hljs-attr">"aggregations"</span>: [
               {
                   <span class="hljs-attr">"type"</span>: <span class="hljs-string">"longSum"</span>,
                   <span class="hljs-attr">"name"</span>: <span class="hljs-string">"added"</span>,
                   <span class="hljs-attr">"fieldName"</span>: <span class="hljs-string">"added"</span>
               }
           ],
           <span class="hljs-attr">"intervals"</span>: [
               <span class="hljs-string">"2015-09-12/2015-09-13"</span>
           ]
       }
   }
</code></pre>
<p>There are 2 parts in a view query:</p>
<table>
<thead>
<tr><th>Field</th><th>Description</th><th>Required</th></tr>
</thead>
<tbody>
<tr><td>queryType</td><td>The query type. This should always be view</td><td>yes</td></tr>
<tr><td>query</td><td>The real query of this <code>view</code> query. The real query must be <a href="/docs/0.17.1/querying/groupbyquery.html">groupBy</a>, <a href="/docs/0.17.1/querying/topnquery.html">topN</a>, or <a href="/docs/0.17.1/querying/timeseriesquery.html">timeseries</a> type.</td><td>yes</td></tr>
</tbody>
</table>
<p><strong>Note that Materialized View is currently designated as experimental. Please make sure the time of all processes are the same and increase monotonically. Otherwise, some unexpected errors may happen on query results.</strong></p>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/0.17.1/development/extensions-contrib/kafka-emitter.html"><span class="arrow-prev">← </span><span>Kafka Emitter</span></a><a class="docs-next button" href="/docs/0.17.1/development/extensions-contrib/momentsketch-quantiles.html"><span>Moment Sketches for Approximate Quantiles module</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#materialized-view-maintenance">Materialized-view-maintenance</a></li><li><a href="#materialized-view-selection">Materialized-view-selection</a></li></ul></nav></div><footer class="nav-footer druid-footer" id="footer"><div class="container"><div class="text-center"><p><a href="/technology">Technology</a> · <a href="/use-cases">Use Cases</a> · <a href="/druid-powered">Powered by Druid</a> · <a href="/docs/0.17.1/">Docs</a> · <a href="/community/">Community</a> · <a href="/downloads.html">Download</a> · <a href="/faq">FAQ</a></p></div><div class="text-center"><a title="Join the user group" href="https://groups.google.com/forum/#!forum/druid-user" target="_blank"><span class="fa fa-comments"></span></a> · <a title="Follow Druid" href="https://twitter.com/druidio" target="_blank"><span class="fab fa-twitter"></span></a> · <a title="Download via Apache" href="https://www.apache.org/dyn/closer.cgi?path=/incubator/druid/{{ site.druid_versions[0].versions[0].version }}/apache-druid-{{ site.druid_versions[0].versions[0].version }}-bin.tar.gz" target="_blank"><span class="fas fa-feather"></span></a> · <a title="GitHub" href="https://github.com/apache/druid" target="_blank"><span class="fab fa-github"></span></a></div><div class="text-center license">Copyright © 2019 <a href="https://www.apache.org/" target="_blank">Apache Software Foundation</a>.<br/>Except where otherwise noted, licensed under <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA 4.0</a>.<br/>Apache Druid, Druid, and the Druid logo are either registered trademarks or trademarks of The Apache Software Foundation in the United States and other countries.</div></div></footer></div><script type="text/javascript" src="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.js"></script><script>
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