<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Cached Lookup Module · Apache Druid</title><meta name="viewport" content="width=device-width"/><link rel="canonical" href="https://druid.apache.org/docs/0.16.1-incubating/development/extensions-core/druid-lookups.html"/><meta name="generator" content="Docusaurus"/><meta name="description" content="&lt;!--"/><meta name="docsearch:language" content="en"/><meta name="docsearch:version" content="../../incubator-druid-website-src/" /><meta property="og:title" content="Cached Lookup Module · 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>
              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/0.16.1-incubating/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/0.16.1-incubating/design/index.html">Introduction to Apache Druid</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/index.html">Quickstart</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/single-server.html">Single server deployment</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/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/0.16.1-incubating/tutorials/tutorial-batch.html">Loading files natively</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-kafka.html">Load from Apache Kafka</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-batch-hadoop.html">Load from Apache Hadoop</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-query.html">Querying data</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-rollup.html">Roll-up</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-retention.html">Configuring data retention</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-update-data.html">Updating existing data</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-compaction.html">Compacting segments</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-delete-data.html">Deleting data</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-ingestion-spec.html">Writing an ingestion spec</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-transform-spec.html">Transforming input data</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/tutorials/tutorial-kerberos-hadoop.html">Kerberized HDFS deep storage</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/0.16.1-incubating/design/architecture.html">Design</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/segments.html">Segments</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/processes.html">Processes and servers</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/dependencies/deep-storage.html">Deep storage</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/dependencies/metadata-storage.html">Metadata storage</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/dependencies/zookeeper.html">ZooKeeper</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Data 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/0.16.1-incubating/ingestion/index.html">Ingestion</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/ingestion/data-formats.html">Data formats</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/ingestion/schema-design.html">Schema design tips</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/ingestion/data-management.html">Data management</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Stream ingestion</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/kafka-ingestion.html">Apache Kafka</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/kinesis-ingestion.html">Amazon Kinesis</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/ingestion/tranquility.html">Tranquility</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Batch ingestion</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/ingestion/native-batch.html">Native batch</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/ingestion/hadoop.html">Hadoop-based</a></li></ul></div><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/ingestion/tasks.html">Task reference</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/ingestion/faq.html">Troubleshooting FAQ</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"><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/sql.html">Druid SQL</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Native query types</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/querying.html">Making native queries</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/timeseriesquery.html">Timeseries</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/topnquery.html">TopN</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/groupbyquery.html">GroupBy</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/scan-query.html">Scan</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/timeboundaryquery.html">TimeBoundary</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/segmentmetadataquery.html">SegmentMetadata</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/datasourcemetadataquery.html">DatasourceMetadata</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/searchquery.html">Search</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/select-query.html">Select</a></li></ul></div><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/multi-value-dimensions.html">Multi-value dimensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/lookups.html">Lookups</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/joins.html">Joins</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/multitenancy.html">Multitenancy considerations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/caching.html">Query caching</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/geo.html">Spatial filters</a></li></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/0.16.1-incubating/configuration/index.html">Configuration reference</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions.html">Extensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/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/0.16.1-incubating/operations/management-uis.html">Management UIs</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/basic-cluster-tuning.html">Basic cluster tuning</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/api-reference.html">API reference</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/high-availability.html">High availability</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/rolling-updates.html">Rolling updates</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/rule-configuration.html">Retaining or automatically dropping data</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/metrics.html">Metrics</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/alerts.html">Alerts</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/other-hadoop.html">Working with different versions of Apache Hadoop</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/http-compression.html">HTTP compression</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/recommendations.html">Recommendations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/tls-support.html">TLS support</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/password-provider.html">Password providers</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/dump-segment.html">dump-segment tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/reset-cluster.html">reset-cluster tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/insert-segment-to-db.html">insert-segment-to-db tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/pull-deps.html">pull-deps tool</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Misc</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/deep-storage-migration.html">Deep storage migration</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/druid-console.html">Web console</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/export-metadata.html">Export Metadata Tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/getting-started.html">Getting started with Apache Druid</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/metadata-migration.html">Metadata Migration</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/operations/segment-optimization.html">Segment Size Optimization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/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/0.16.1-incubating/development/overview.html">Developing on Druid</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/modules.html">Creating extensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/javascript.html">JavaScript functionality</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/build.html">Build from source</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/versioning.html">Versioning</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/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/0.16.1-incubating/misc/math-expr.html">Expressions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/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/0.16.1-incubating/comparisons/druid-vs-elasticsearch.html">Apache Druid vs Elasticsearch</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/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/0.16.1-incubating/comparisons/druid-vs-kudu.html">Apache Druid vs Kudu</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/comparisons/druid-vs-redshift.html">Apache Druid vs Redshift</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/comparisons/druid-vs-spark.html">Apache Druid vs Spark</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/comparisons/druid-vs-sql-on-hadoop.html">Apache Druid vs SQL-on-Hadoop</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/auth.html">Authentication and Authorization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/broker.html">Broker</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/coordinator.html">Coordinator Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/historical.html">Historical Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/indexer.html">Indexer Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/indexing-service.html">Indexing Service</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/middlemanager.html">MiddleManager Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/overlord.html">Overlord Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/router.html">Router Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/design/peons.html">Peons</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/approximate-histograms.html">Approximate Histogram aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/avro.html">Apache Avro</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/bloom-filter.html">Bloom Filter</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/datasketches-extension.html">DataSketches extension</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/datasketches-hll.html">DataSketches HLL Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/datasketches-quantiles.html">DataSketches Quantiles Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/datasketches-theta.html">DataSketches Theta Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/datasketches-tuple.html">DataSketches Tuple Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/druid-basic-security.html">Basic Security</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/druid-kerberos.html">Kerberos</a></li><li class="navListItem navListItemActive"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/druid-lookups.html">Cached Lookup Module</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/google.html">Google Cloud Storage</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/hdfs.html">HDFS</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/kafka-extraction-namespace.html">Apache Kafka Lookups</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/lookups-cached-global.html">Globally Cached Lookups</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/mysql.html">MySQL Metadata Store</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/orc.html">ORC Extension</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/parquet.html">Apache Parquet Extension</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/postgresql.html">PostgreSQL Metadata Store</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/protobuf.html">Protobuf</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/s3.html">S3-compatible</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/simple-client-sslcontext.html">Simple SSLContext Provider Module</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/stats.html">Stats aggregator</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-core/test-stats.html">Test Stats Aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/ambari-metrics-emitter.html">Ambari Metrics Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/azure.html">Microsoft Azure</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/cassandra.html">Apache Cassandra</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/cloudfiles.html">Rackspace Cloud Files</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/distinctcount.html">DistinctCount Aggregator</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/graphite.html">Graphite Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/aggregations.html">Aggregations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/datasource.html">Datasources</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/dimensionspecs.html">Transforming Dimension Values</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/filters.html">Query Filters</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/granularities.html">Aggregation Granularity</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/having.html">Filter groupBy query results</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/hll-old.html">Cardinality/HyperUnique aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/limitspec.html">Sort groupBy query results</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/post-aggregations.html">Post-Aggregations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/query-context.html">Query context</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/searchqueryspec.html">Refining search queries</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/sorting-orders.html">Sorting Orders</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/topnmetricspec.html">TopNMetricSpec</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/querying/virtual-columns.html">Virtual Columns</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/influx.html">InfluxDB Line Protocol Parser</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/influxdb-emitter.html">InfluxDB Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/kafka-emitter.html">Kafka Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/materialized-view.html">Materialized View</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/momentsketch-quantiles.html">Moment Sketches for Approximate Quantiles module</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/moving-average-query.html">development/extensions-contrib/moving-average-query</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/opentsdb-emitter.html">OpenTSDB Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/redis-cache.html">Druid Redis Cache</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/sqlserver.html">Microsoft SQLServer</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/statsd.html">StatsD Emitter</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/tdigestsketch-quantiles.html">T-Digest Quantiles Sketch module</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/thrift.html">Thrift</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/development/extensions-contrib/time-min-max.html">Timestamp Min/Max aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/0.16.1-incubating/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"><div class="wrapper"><div class="post"><header class="postHeader"><a class="edit-page-link button" href="https://github.com/apache/incubator-druid/edit/master/docs/development/extensions-core/druid-lookups.md" target="_blank" rel="noreferrer noopener">Edit</a><h1 class="postHeaderTitle">Cached Lookup Module</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.
  -->
<blockquote>
<p>Please note that this is an experimental module and the development/testing still at early stage. Feel free to try it and give us your feedback.</p>
</blockquote>
<h2><a class="anchor" aria-hidden="true" id="description"></a><a href="#description" 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>Description</h2>
<p>This Apache Druid (incubating) module provides a per-lookup caching mechanism for JDBC data sources.
The main goal of this cache is to speed up the access to a high latency lookup sources and to provide a caching isolation for every lookup source.
Thus user can define various caching strategies or and implementation per lookup, even if the source is the same.
This module can be used side to side with other lookup module like the global cached lookup module.</p>
<p>To use this extension please make sure to  <a href="/docs/0.16.1-incubating/development/extensions.html#loading-extensions">include</a> <code>druid-lookups-cached-single</code> as an extension.</p>
<h2><a class="anchor" aria-hidden="true" id="architecture"></a><a href="#architecture" 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>Architecture</h2>
<p>Generally speaking this module can be divided into two main component, namely, the data fetcher layer and caching layer.</p>
<h3><a class="anchor" aria-hidden="true" id="data-fetcher-layer"></a><a href="#data-fetcher-layer" 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>Data Fetcher layer</h3>
<p>First part is the data fetcher layer API <code>DataFetcher</code>, that exposes a set of fetch methods to fetch data from the actual Lookup dimension source.
For instance <code>JdbcDataFetcher</code> provides an implementation of <code>DataFetcher</code> that can be used to fetch key/value from a RDBMS via JDBC driver.
If you need new type of data fetcher, all you need to do, is to implement the interface <code>DataFetcher</code> and load it via another druid module.</p>
<h3><a class="anchor" aria-hidden="true" id="caching-layer"></a><a href="#caching-layer" 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>Caching layer</h3>
<p>This extension comes with two different caching strategies. First strategy is a poll based and the second is a load based.</p>
<h4><a class="anchor" aria-hidden="true" id="poll-lookup-cache"></a><a href="#poll-lookup-cache" 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>Poll lookup cache</h4>
<p>The poll strategy cache strategy will fetch and swap all the pair of key/values periodically from the lookup source.
Hence, user should make sure that the cache can fit all the data.
The current implementation provides 2 type of poll cache, the first is on-heap (uses immutable map), while the second uses MapDB based off-heap map.
User can also implement a different lookup polling cache by implementing <code>PollingCacheFactory</code> and <code>PollingCache</code> interfaces.</p>
<h4><a class="anchor" aria-hidden="true" id="loading-lookup"></a><a href="#loading-lookup" 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>Loading lookup</h4>
<p>Loading cache strategy will load the key/value pair upon request on the key it self, the general algorithm is load key if absent.
Once the key/value  pair is loaded eviction will occur according to the cache eviction policy.
This module comes with two loading lookup implementation, the first is on-heap backed by a Guava cache implementation, the second is MapDB off-heap implementation.
Both implementations offer various eviction strategies.
Same for Loading cache, developer can implement a new type of loading cache by implementing <code>LookupLoadingCache</code> interface.</p>
<h2><a class="anchor" aria-hidden="true" id="configuration-and-operation"></a><a href="#configuration-and-operation" 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>Configuration and Operation:</h2>
<h3><a class="anchor" aria-hidden="true" id="polling-lookup"></a><a href="#polling-lookup" 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>Polling Lookup</h3>
<p><strong>Note that the current implementation of <code>offHeapPolling</code> and <code>onHeapPolling</code> will create two caches one to lookup value based on key and the other to reverse lookup the key from value</strong></p>
<table>
<thead>
<tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr>
</thead>
<tbody>
<tr><td>dataFetcher</td><td>JSON object</td><td>Specifies the lookup data fetcher type  to use in order to fetch data</td><td>yes</td><td>null</td></tr>
<tr><td>cacheFactory</td><td>JSON Object</td><td>Cache factory implementation</td><td>no</td><td>onHeapPolling</td></tr>
<tr><td>pollPeriod</td><td>Period</td><td>polling period</td><td>no</td><td>null (poll once)</td></tr>
</tbody>
</table>
<h5><a class="anchor" aria-hidden="true" id="example-of-polling-on-heap-lookup"></a><a href="#example-of-polling-on-heap-lookup" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example of Polling On-heap Lookup</h5>
<p>This example demonstrates a polling cache that will update its on-heap cache every 10 minutes</p>
<pre><code class="hljs css language-json">{
    <span class="hljs-attr">"type"</span>:<span class="hljs-string">"pollingLookup"</span>,
   <span class="hljs-attr">"pollPeriod"</span>:<span class="hljs-string">"PT10M"</span>,
   <span class="hljs-attr">"dataFetcher"</span>:{ <span class="hljs-attr">"type"</span>:<span class="hljs-string">"jdbcDataFetcher"</span>, <span class="hljs-attr">"connectorConfig"</span>:<span class="hljs-string">"jdbc://mysql://localhost:3306/my_data_base"</span>, <span class="hljs-attr">"table"</span>:<span class="hljs-string">"lookup_table_name"</span>, <span class="hljs-attr">"keyColumn"</span>:<span class="hljs-string">"key_column_name"</span>, <span class="hljs-attr">"valueColumn"</span>: <span class="hljs-string">"value_column_name"</span>},
   <span class="hljs-attr">"cacheFactory"</span>:{<span class="hljs-attr">"type"</span>:<span class="hljs-string">"onHeapPolling"</span>}
}

</code></pre>
<h5><a class="anchor" aria-hidden="true" id="example-polling-off-heap-lookup"></a><a href="#example-polling-off-heap-lookup" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example Polling Off-heap Lookup</h5>
<p>This example demonstrates an off-heap lookup that will be cached once and never swapped <code>(pollPeriod == null)</code></p>
<pre><code class="hljs css language-json">{
    <span class="hljs-attr">"type"</span>:<span class="hljs-string">"pollingLookup"</span>,
   <span class="hljs-attr">"dataFetcher"</span>:{ <span class="hljs-attr">"type"</span>:<span class="hljs-string">"jdbcDataFetcher"</span>, <span class="hljs-attr">"connectorConfig"</span>:<span class="hljs-string">"jdbc://mysql://localhost:3306/my_data_base"</span>, <span class="hljs-attr">"table"</span>:<span class="hljs-string">"lookup_table_name"</span>, <span class="hljs-attr">"keyColumn"</span>:<span class="hljs-string">"key_column_name"</span>, <span class="hljs-attr">"valueColumn"</span>: <span class="hljs-string">"value_column_name"</span>},
   <span class="hljs-attr">"cacheFactory"</span>:{<span class="hljs-attr">"type"</span>:<span class="hljs-string">"offHeapPolling"</span>}
}

</code></pre>
<h3><a class="anchor" aria-hidden="true" id="loading-lookup-1"></a><a href="#loading-lookup-1" 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>Loading lookup</h3>
<table>
<thead>
<tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr>
</thead>
<tbody>
<tr><td>dataFetcher</td><td>JSON object</td><td>Specifies the lookup data fetcher type  to use in order to fetch data</td><td>yes</td><td>null</td></tr>
<tr><td>loadingCacheSpec</td><td>JSON Object</td><td>Lookup cache spec implementation</td><td>yes</td><td>null</td></tr>
<tr><td>reverseLoadingCacheSpec</td><td>JSON Object</td><td>Reverse lookup cache  implementation</td><td>yes</td><td>null</td></tr>
</tbody>
</table>
<h5><a class="anchor" aria-hidden="true" id="example-loading-on-heap-guava"></a><a href="#example-loading-on-heap-guava" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example Loading On-heap Guava</h5>
<p>Guava cache configuration spec.</p>
<table>
<thead>
<tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr>
</thead>
<tbody>
<tr><td>concurrencyLevel</td><td>int</td><td>Allowed concurrency among update operations</td><td>no</td><td>4</td></tr>
<tr><td>initialCapacity</td><td>int</td><td>Initial capacity size</td><td>no</td><td>null</td></tr>
<tr><td>maximumSize</td><td>long</td><td>Specifies the maximum number of entries the cache may contain.</td><td>no</td><td>null (infinite capacity)</td></tr>
<tr><td>expireAfterAccess</td><td>long</td><td>Specifies the eviction time after last read in milliseconds.</td><td>no</td><td>null (No read-time-based eviction when set to null)</td></tr>
<tr><td>expireAfterWrite</td><td>long</td><td>Specifies the eviction time after last write in milliseconds.</td><td>no</td><td>null (No write-time-based eviction when set to null)</td></tr>
</tbody>
</table>
<pre><code class="hljs css language-json">{
   <span class="hljs-attr">"type"</span>:<span class="hljs-string">"loadingLookup"</span>,
   <span class="hljs-attr">"dataFetcher"</span>:{ <span class="hljs-attr">"type"</span>:<span class="hljs-string">"jdbcDataFetcher"</span>, <span class="hljs-attr">"connectorConfig"</span>:<span class="hljs-string">"jdbc://mysql://localhost:3306/my_data_base"</span>, <span class="hljs-attr">"table"</span>:<span class="hljs-string">"lookup_table_name"</span>, <span class="hljs-attr">"keyColumn"</span>:<span class="hljs-string">"key_column_name"</span>, <span class="hljs-attr">"valueColumn"</span>: <span class="hljs-string">"value_column_name"</span>},
   <span class="hljs-attr">"loadingCacheSpec"</span>:{<span class="hljs-attr">"type"</span>:<span class="hljs-string">"guava"</span>},
   <span class="hljs-attr">"reverseLoadingCacheSpec"</span>:{<span class="hljs-attr">"type"</span>:<span class="hljs-string">"guava"</span>, <span class="hljs-attr">"maximumSize"</span>:<span class="hljs-number">500000</span>, <span class="hljs-attr">"expireAfterAccess"</span>:<span class="hljs-number">100000</span>, <span class="hljs-attr">"expireAfterAccess"</span>:<span class="hljs-number">10000</span>}
}
</code></pre>
<h5><a class="anchor" aria-hidden="true" id="example-loading-off-heap-mapdb"></a><a href="#example-loading-off-heap-mapdb" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example Loading Off-heap MapDB</h5>
<p>Off heap cache is backed by <a href="http://www.mapdb.org/">MapDB</a> implementation. MapDB is using direct memory as memory pool, please take that into account when limiting the JVM direct memory setup.</p>
<table>
<thead>
<tr><th>Field</th><th>Type</th><th>Description</th><th>Required</th><th>default</th></tr>
</thead>
<tbody>
<tr><td>maxStoreSize</td><td>double</td><td>maximal size of store in GB, if store is larger entries will start expiring</td><td>no</td><td>0</td></tr>
<tr><td>maxEntriesSize</td><td>long</td><td>Specifies the maximum number of entries the cache may contain.</td><td>no</td><td>0 (infinite capacity)</td></tr>
<tr><td>expireAfterAccess</td><td>long</td><td>Specifies the eviction time after last read in milliseconds.</td><td>no</td><td>0 (No read-time-based eviction when set to null)</td></tr>
<tr><td>expireAfterWrite</td><td>long</td><td>Specifies the eviction time after last write in milliseconds.</td><td>no</td><td>0 (No write-time-based eviction when set to null)</td></tr>
</tbody>
</table>
<pre><code class="hljs css language-json">{
   <span class="hljs-attr">"type"</span>:<span class="hljs-string">"loadingLookup"</span>,
   <span class="hljs-attr">"dataFetcher"</span>:{ <span class="hljs-attr">"type"</span>:<span class="hljs-string">"jdbcDataFetcher"</span>, <span class="hljs-attr">"connectorConfig"</span>:<span class="hljs-string">"jdbc://mysql://localhost:3306/my_data_base"</span>, <span class="hljs-attr">"table"</span>:<span class="hljs-string">"lookup_table_name"</span>, <span class="hljs-attr">"keyColumn"</span>:<span class="hljs-string">"key_column_name"</span>, <span class="hljs-attr">"valueColumn"</span>: <span class="hljs-string">"value_column_name"</span>},
   <span class="hljs-attr">"loadingCacheSpec"</span>:{<span class="hljs-attr">"type"</span>:<span class="hljs-string">"mapDb"</span>, <span class="hljs-attr">"maxEntriesSize"</span>:<span class="hljs-number">100000</span>},
   <span class="hljs-attr">"reverseLoadingCacheSpec"</span>:{<span class="hljs-attr">"type"</span>:<span class="hljs-string">"mapDb"</span>, <span class="hljs-attr">"maxStoreSize"</span>:<span class="hljs-number">5</span>, <span class="hljs-attr">"expireAfterAccess"</span>:<span class="hljs-number">100000</span>, <span class="hljs-attr">"expireAfterAccess"</span>:<span class="hljs-number">10000</span>}
}
</code></pre>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/0.16.1-incubating/development/extensions-core/druid-kerberos.html"><span class="arrow-prev">← </span><span>Kerberos</span></a><a class="docs-next button" href="/docs/0.16.1-incubating/development/extensions-core/google.html"><span>Google Cloud Storage</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#description">Description</a></li><li><a href="#architecture">Architecture</a><ul class="toc-headings"><li><a href="#data-fetcher-layer">Data Fetcher layer</a></li><li><a href="#caching-layer">Caching layer</a></li></ul></li><li><a href="#configuration-and-operation">Configuration and Operation:</a><ul class="toc-headings"><li><a href="#polling-lookup">Polling Lookup</a></li><li><a href="#loading-lookup-1">Loading lookup</a></li></ul></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/0.16.1-incubating/latest">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/incubator-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>
                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({
                
                apiKey: '2de99082a9f38e49dfaa059bbe4c901d',
                indexName: 'apache_druid',
                inputSelector: '#search_input_react',
                algoliaOptions: {"facetFilters":["language:en","version:../../incubator-druid-website-src/"]}
              });
            </script></body></html>