<!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, initial-scale=1.0"/><link rel="canonical" href="https://druid.apache.org/docs/26.0.0/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="26.0.0" /><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/npm/docsearch.js@2/dist/cdn/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>
              window.dataLayer = window.dataLayer || [];
              function gtag(){dataLayer.push(arguments); }
              gtag('js', new Date());
              gtag('config', 'UA-131010415-1');
            </script><link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.2/css/all.css"/><link rel="stylesheet" href="/css/code-block-buttons.css"/><script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.4/clipboard.min.js"></script><script type="text/javascript" src="/js/code-block-buttons.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="/"><img class="logo" src="/img/druid_nav.png" alt="Apache Druid"/></a><div class="navigationWrapper navigationSlider"><nav class="slidingNav"><ul class="nav-site nav-site-internal"><li class=""><a href="/technology" target="_self">Technology</a></li><li class=""><a href="/use-cases" target="_self">Use Cases</a></li><li class=""><a href="/druid-powered" target="_self">Powered By</a></li><li class="siteNavGroupActive"><a href="/docs/26.0.0/design/index.html" target="_self">Docs</a></li><li class=""><a href="/community/" target="_self">Community</a></li><li class=""><a href="https://www.apache.org" target="_self">Apache</a></li><li class=""><a href="/downloads.html" target="_self">Download</a></li><li class="navSearchWrapper reactNavSearchWrapper"><input type="text" id="search_input_react" placeholder="Search" title="Search"/></li></ul></nav></div></header></div></div><div class="navPusher"><div class="docMainWrapper wrapper"><div class="docsNavContainer" id="docsNav"><nav class="toc"><div class="toggleNav"><section class="navWrapper wrapper"><div class="navBreadcrumb wrapper"><div class="navToggle" id="navToggler"><div class="hamburger-menu"><div class="line1"></div><div class="line2"></div><div class="line3"></div></div></div><h2><i>›</i><span>Hidden</span></h2><div class="tocToggler" id="tocToggler"><i class="icon-toc"></i></div></div><div class="navGroups"><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Getting started<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/index.html">Introduction to Apache Druid</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/index.html">Quickstart (local)</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/single-server.html">Single server deployment</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/cluster.html">Clustered deployment</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Tutorials<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-batch.html">Load files natively</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-msq-extern.html">Load files using SQL 🆕</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-kafka.html">Load from Apache Kafka</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-batch-hadoop.html">Load from Apache Hadoop</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-query.html">Querying data</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-rollup.html">Roll-up</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-sketches-theta.html">Theta sketches</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-retention.html">Configuring data retention</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-update-data.html">Updating existing data</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-compaction.html">Compacting segments</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-delete-data.html">Deleting data</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-ingestion-spec.html">Writing an ingestion spec</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-transform-spec.html">Transforming input data</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/docker.html">Tutorial: Run with Docker</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-kerberos-hadoop.html">Kerberized HDFS deep storage</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-msq-convert-spec.html">Convert ingestion spec to SQL</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-sql-query-view.html">Get to know Query view</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-unnest-arrays.html">Unnesting arrays</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-jupyter-index.html">Jupyter Notebook tutorials</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/tutorials/tutorial-jdbc.html">JDBC connector</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Design<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/architecture.html">Design</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/segments.html">Segments</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/processes.html">Processes and servers</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/dependencies/deep-storage.html">Deep storage</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/dependencies/metadata-storage.html">Metadata storage</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/dependencies/zookeeper.html">ZooKeeper</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Ingestion<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/index.html">Ingestion</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/data-formats.html">Data formats</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/data-model.html">Data model</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/rollup.html">Data rollup</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/partitioning.html">Partitioning</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/ingestion-spec.html">Ingestion spec</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/schema-design.html">Schema design tips</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Stream ingestion</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/kafka-ingestion.html">Apache Kafka ingestion</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/kafka-supervisor-reference.html">Apache Kafka supervisor</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/kafka-supervisor-operations.html">Apache Kafka operations</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/kinesis-ingestion.html">Amazon Kinesis</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Batch ingestion</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/native-batch.html">Native batch</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/native-batch-input-sources.html">Native batch: input sources</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/migrate-from-firehose.html">Migrate from firehose</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/hadoop.html">Hadoop-based</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">SQL-based ingestion 🆕</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/multi-stage-query/index.html">Overview</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/multi-stage-query/concepts.html">Key concepts</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/multi-stage-query/api.html">API</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/multi-stage-query/security.html">Security</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/multi-stage-query/examples.html">Examples</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/multi-stage-query/reference.html">Reference</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/multi-stage-query/known-issues.html">Known issues</a></li></ul></div><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/tasks.html">Task reference</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/faq.html">Troubleshooting FAQ</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Data management<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/data-management/index.html">Overview</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/data-management/update.html">Data updates</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/data-management/delete.html">Data deletion</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/data-management/schema-changes.html">Schema changes</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/data-management/compaction.html">Compaction</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/data-management/automatic-compaction.html">Automatic compaction</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Querying<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Druid SQL</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql.html">Overview and syntax</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-data-types.html">SQL data types</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-operators.html">Operators</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-scalar.html">Scalar functions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-aggregations.html">Aggregation functions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-multivalue-string-functions.html">Multi-value string functions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-json-functions.html">JSON functions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-functions.html">All functions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-api.html">Druid SQL API</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-jdbc.html">JDBC driver API</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-query-context.html">SQL query context</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-metadata-tables.html">SQL metadata tables</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sql-translation.html">SQL query translation</a></li></ul></div><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/querying.html">Native queries</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/query-execution.html">Query execution</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/troubleshooting.html">Troubleshooting</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Concepts</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/datasource.html">Datasources</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/joins.html">Joins</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/lookups.html">Lookups</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/multi-value-dimensions.html">Multi-value dimensions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/nested-columns.html">Nested columns</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/multitenancy.html">Multitenancy</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/caching.html">Query caching</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/using-caching.html">Using query caching</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/query-context.html">Query context</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Native query types</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/timeseriesquery.html">Timeseries</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/topnquery.html">TopN</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/groupbyquery.html">GroupBy</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/scan-query.html">Scan</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/searchquery.html">Search</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/timeboundaryquery.html">TimeBoundary</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/segmentmetadataquery.html">SegmentMetadata</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/datasourcemetadataquery.html">DatasourceMetadata</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Native query components</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/filters.html">Filters</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/granularities.html">Granularities</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/dimensionspecs.html">Dimensions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/aggregations.html">Aggregations</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/post-aggregations.html">Post-aggregations</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/misc/math-expr.html">Expressions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/having.html">Having filters (groupBy)</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/limitspec.html">Sorting and limiting (groupBy)</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/topnmetricspec.html">Sorting (topN)</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/sorting-orders.html">String comparators</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/virtual-columns.html">Virtual columns</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/geo.html">Spatial filters</a></li></ul></div></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Configuration<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/configuration/index.html">Configuration reference</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions.html">Extensions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/configuration/logging.html">Logging</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Operations<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/web-console.html">Web console</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/java.html">Java runtime</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Security</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/security-overview.html">Security overview</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/security-user-auth.html">User authentication and authorization</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/auth-ldap.html">LDAP auth</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/password-provider.html">Password providers</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/dynamic-config-provider.html">Dynamic Config Providers</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/tls-support.html">TLS support</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Performance tuning</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/basic-cluster-tuning.html">Basic cluster tuning</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/segment-optimization.html">Segment size optimization</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/mixed-workloads.html">Mixed workloads</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/http-compression.html">HTTP compression</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/clean-metadata-store.html">Automated metadata cleanup</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Monitoring</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/request-logging.html">Request logging</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/metrics.html">Metrics</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/alerts.html">Alerts</a></li></ul></div><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/api-reference.html">API reference</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/high-availability.html">High availability</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/rolling-updates.html">Rolling updates</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/rule-configuration.html">Using rules to drop and retain data</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/other-hadoop.html">Working with different versions of Apache Hadoop</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Misc</h4><ul><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/dump-segment.html">dump-segment tool</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/reset-cluster.html">reset-cluster tool</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/insert-segment-to-db.html">insert-segment-to-db tool</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/pull-deps.html">pull-deps tool</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/deep-storage-migration.html">Deep storage migration</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/export-metadata.html">Export Metadata Tool</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/metadata-migration.html">Metadata Migration</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/use_sbt_to_build_fat_jar.html">Content for build.sbt</a></li></ul></div></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Development<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/overview.html">Developing on Druid</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/modules.html">Creating extensions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/javascript.html">JavaScript functionality</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/build.html">Build from source</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/versioning.html">Versioning</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/experimental.html">Experimental features</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Misc<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/misc/papers-and-talks.html">Papers</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Hidden<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/26.0.0/comparisons/druid-vs-elasticsearch.html">Apache Druid vs Elasticsearch</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/comparisons/druid-vs-key-value.html">Apache Druid vs. Key/Value Stores (HBase/Cassandra/OpenTSDB)</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/comparisons/druid-vs-kudu.html">Apache Druid vs Kudu</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/comparisons/druid-vs-redshift.html">Apache Druid vs Redshift</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/comparisons/druid-vs-spark.html">Apache Druid vs Spark</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/comparisons/druid-vs-sql-on-hadoop.html">Apache Druid vs SQL-on-Hadoop</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/auth.html">Authentication and Authorization</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/broker.html">Broker</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/coordinator.html">Coordinator Process</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/historical.html">Historical Process</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/indexer.html">Indexer Process</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/indexing-service.html">Indexing Service</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/middlemanager.html">MiddleManager Process</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/overlord.html">Overlord Process</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/router.html">Router Process</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/design/peons.html">Peons</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/approximate-histograms.html">Approximate Histogram aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/avro.html">Apache Avro</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/azure.html">Microsoft Azure</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/bloom-filter.html">Bloom Filter</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/datasketches-extension.html">DataSketches extension</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/datasketches-hll.html">DataSketches HLL Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/datasketches-quantiles.html">DataSketches Quantiles Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/datasketches-theta.html">DataSketches Theta Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/datasketches-tuple.html">DataSketches Tuple Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/druid-basic-security.html">Basic Security</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/druid-kerberos.html">Kerberos</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/druid-lookups.html">Cached Lookup Module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/druid-ranger-security.html">Apache Ranger Security</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/google.html">Google Cloud Storage</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/hdfs.html">HDFS</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/kafka-extraction-namespace.html">Apache Kafka Lookups</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/lookups-cached-global.html">Globally Cached Lookups</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/mysql.html">MySQL Metadata Store</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/orc.html">ORC Extension</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/druid-pac4j.html">Druid pac4j based Security extension</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/parquet.html">Apache Parquet Extension</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/postgresql.html">PostgreSQL Metadata Store</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/protobuf.html">Protobuf</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/s3.html">S3-compatible</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/simple-client-sslcontext.html">Simple SSLContext Provider Module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/stats.html">Stats aggregator</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/test-stats.html">Test Stats Aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/druid-aws-rds.html">Druid AWS RDS Module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-core/kubernetes.html">Kubernetes</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/ambari-metrics-emitter.html">Ambari Metrics Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/cassandra.html">Apache Cassandra</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/cloudfiles.html">Rackspace Cloud Files</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/distinctcount.html">DistinctCount Aggregator</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/graphite.html">Graphite Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/influx.html">InfluxDB Line Protocol Parser</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/influxdb-emitter.html">InfluxDB Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/kafka-emitter.html">Kafka Emitter</a></li><li class="navListItem navListItemActive"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/materialized-view.html">Materialized View</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/momentsketch-quantiles.html">Moment Sketches for Approximate Quantiles module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/moving-average-query.html">Moving Average Query</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/opentsdb-emitter.html">OpenTSDB Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/redis-cache.html">Druid Redis Cache</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/sqlserver.html">Microsoft SQLServer</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/statsd.html">StatsD Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/tdigestsketch-quantiles.html">T-Digest Quantiles Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/thrift.html">Thrift</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/time-min-max.html">Timestamp Min/Max aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/gce-extensions.html">GCE Extensions</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/aliyun-oss.html">Aliyun OSS</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/development/extensions-contrib/prometheus.html">Prometheus Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/operations/kubernetes.html">kubernetes</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/hll-old.html">Cardinality/HyperUnique aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/querying/select-query.html">Select</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/native-batch-firehose.html">Firehose (deprecated)</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/native-batch-simple-task.html">Native batch (simple)</a></li><li class="navListItem"><a class="navItem" href="/docs/26.0.0/ingestion/standalone-realtime.html">Realtime Process</a></li></ul></div></div></section></div><script>
            var coll = document.getElementsByClassName('collapsible');
            var checkActiveCategory = true;
            for (var i = 0; i < coll.length; i++) {
              var links = coll[i].nextElementSibling.getElementsByTagName('*');
              if (checkActiveCategory){
                for (var j = 0; j < links.length; j++) {
                  if (links[j].classList.contains('navListItemActive')){
                    coll[i].nextElementSibling.classList.toggle('hide');
                    coll[i].childNodes[1].classList.toggle('rotate');
                    checkActiveCategory = false;
                    break;
                  }
                }
              }

              coll[i].addEventListener('click', function() {
                var arrow = this.childNodes[1];
                arrow.classList.toggle('rotate');
                var content = this.nextElementSibling;
                content.classList.toggle('hide');
              });
            }

            document.addEventListener('DOMContentLoaded', function() {
              createToggler('#navToggler', '#docsNav', 'docsSliderActive');
              createToggler('#tocToggler', 'body', 'tocActive');

              var headings = document.querySelector('.toc-headings');
              headings && headings.addEventListener('click', function(event) {
                var el = event.target;
                while(el !== headings){
                  if (el.tagName === 'A') {
                    document.body.classList.remove('tocActive');
                    break;
                  } else{
                    el = el.parentNode;
                  }
                }
              }, false);

              function createToggler(togglerSelector, targetSelector, className) {
                var toggler = document.querySelector(togglerSelector);
                var target = document.querySelector(targetSelector);

                if (!toggler) {
                  return;
                }

                toggler.onclick = function(event) {
                  event.preventDefault();

                  target.classList.toggle(className);
                };
              }
            });
        </script></nav></div><div class="container mainContainer docsContainer"><div class="wrapper"><div class="post"><header class="postHeader"><a class="edit-page-link button" href="https://github.com/apache/druid/edit/master/docs/development/extensions-contrib/materialized-view.md" target="_blank" rel="noreferrer noopener">Edit</a><h1 id="__docusaurus" class="postHeaderTitle">Materialized View</h1></header><article><div><span><!--
  ~ Licensed to the Apache Software Foundation (ASF) under one
  ~ or more contributor license agreements.  See the NOTICE file
  ~ distributed with this work for additional information
  ~ regarding copyright ownership.  The ASF licenses this file
  ~ to you under the Apache License, Version 2.0 (the
  ~ "License"); you may not use this file except in compliance
  ~ with the License.  You may obtain a copy of the License at
  ~
  ~   http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing,
  ~ software distributed under the License is distributed on an
  ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  ~ KIND, either express or implied.  See the License for the
  ~ specific language governing permissions and limitations
  ~ under the License.
  -->
<p>To use this Apache Druid feature, make sure to load <code>materialized-view-selection</code> and <code>materialized-view-maintenance</code>. 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/26.0.0/querying/aggregations.html">aggregations</a>.</td><td>yes</td></tr>
<tr><td>tuningConfig</td><td>TuningConfig must be HadoopTuningConfig. See <a href="/docs/26.0.0/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/26.0.0/querying/groupbyquery.html">groupBy</a>, <a href="/docs/26.0.0/querying/topnquery.html">topN</a>, or <a href="/docs/26.0.0/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/26.0.0/development/extensions-contrib/kafka-emitter.html"><span class="arrow-prev">← </span><span>Kafka Emitter</span></a><a class="docs-next button" href="/docs/26.0.0/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/26.0.0/">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 © 2022 <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/npm/docsearch.js@2/dist/cdn/docsearch.min.js"></script><script>
                document.addEventListener('keyup', function(e) {
                  if (e.target !== document.body) {
                    return;
                  }
                  // keyCode for '/' (slash)
                  if (e.keyCode === 191) {
                    const search = document.getElementById('search_input_react');
                    search && search.focus();
                  }
                });
              </script><script>
              var search = docsearch({
                appId: 'CPK9PMSCEY',
                apiKey: 'd4ef4ffe3a2f0c7d1e34b062fd98736b',
                indexName: 'apache_druid',
                inputSelector: '#search_input_react',
                algoliaOptions: {"facetFilters":["language:en","version:26.0.0"]}
              });
            </script></body></html>