<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Bloom Filter · 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/bloom-filter.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="Bloom Filter · 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 navListItemActive"><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"><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/bloom-filter.md" target="_blank" rel="noreferrer noopener">Edit</a><h1 class="postHeaderTitle">Bloom Filter</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>This Apache Druid (incubating) extension adds the ability to both construct bloom filters from query results, and filter query results by testing
against a bloom filter. Make sure to <a href="/docs/0.16.1-incubating/development/extensions.html#loading-extensions">include</a> <code>druid-bloom-filter</code> as an
extension.</p>
<p>A Bloom filter is a probabilistic data structure for performing a set membership check. A bloom filter is a good candidate
to use with Druid for cases where an explicit filter is impossible, e.g. filtering a query against a set of millions of
values.</p>
<p>Following are some characteristics of Bloom filters:</p>
<ul>
<li>Bloom filters are highly space efficient when compared to using a HashSet.</li>
<li>Because of the probabilistic nature of bloom filters, false positive results are possible (element was not actually
inserted into a bloom filter during construction, but <code>test()</code> says true)</li>
<li>False negatives are not possible (if element is present then <code>test()</code> will never say false).</li>
<li>The false positive probability of this implementation is currently fixed at 5%, but increasing the number of entries
that the filter can hold can decrease this false positive rate in exchange for overall size.</li>
<li>Bloom filters are sensitive to number of elements that will be inserted in the bloom filter. During the creation of bloom filter expected number of entries must be specified. If the number of insertions exceed
the specified initial number of entries then false positive probability will increase accordingly.</li>
</ul>
<p>This extension is currently based on <code>org.apache.hive.common.util.BloomKFilter</code> from <code>hive-storage-api</code>. Internally,
this implementation uses Murmur3 as the hash algorithm.</p>
<p>To construct a BloomKFilter externally with Java to use as a filter in a Druid query:</p>
<pre><code class="hljs css language-java">BloomKFilter bloomFilter = <span class="hljs-keyword">new</span> BloomKFilter(<span class="hljs-number">1500</span>);
bloomFilter.addString(<span class="hljs-string">"value 1"</span>);
bloomFilter.addString(<span class="hljs-string">"value 2"</span>);
bloomFilter.addString(<span class="hljs-string">"value 3"</span>);
ByteArrayOutputStream byteArrayOutputStream = <span class="hljs-keyword">new</span> ByteArrayOutputStream();
BloomKFilter.serialize(byteArrayOutputStream, bloomFilter);
String base64Serialized = Base64.encodeBase64String(byteArrayOutputStream.toByteArray());
</code></pre>
<p>This string can then be used in the native or SQL Druid query.</p>
<h2><a class="anchor" aria-hidden="true" id="filtering-queries-with-a-bloom-filter"></a><a href="#filtering-queries-with-a-bloom-filter" 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>Filtering queries with a Bloom Filter</h2>
<h3><a class="anchor" aria-hidden="true" id="json-specification-of-bloom-filter"></a><a href="#json-specification-of-bloom-filter" 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>JSON Specification of Bloom Filter</h3>
<pre><code class="hljs css language-json">{
  <span class="hljs-attr">"type"</span> : <span class="hljs-string">"bloom"</span>,
  <span class="hljs-attr">"dimension"</span> : &lt;dimension_name&gt;,
  <span class="hljs-attr">"bloomKFilter"</span> : &lt;serialized_bytes_for_BloomKFilter&gt;,
  <span class="hljs-attr">"extractionFn"</span> : &lt;extraction_fn&gt;
}
</code></pre>
<table>
<thead>
<tr><th>Property</th><th>Description</th><th>required?</th></tr>
</thead>
<tbody>
<tr><td><code>type</code></td><td>Filter Type. Should always be <code>bloom</code></td><td>yes</td></tr>
<tr><td><code>dimension</code></td><td>The dimension to filter over.</td><td>yes</td></tr>
<tr><td><code>bloomKFilter</code></td><td>Base64 encoded Binary representation of <code>org.apache.hive.common.util.BloomKFilter</code></td><td>yes</td></tr>
<tr><td><code>extractionFn</code></td><td><a href="../../querying/dimensionspecs.html#extraction-functions">Extraction function</a> to apply to the dimension values</td><td>no</td></tr>
</tbody>
</table>
<h3><a class="anchor" aria-hidden="true" id="serialized-format-for-bloomkfilter"></a><a href="#serialized-format-for-bloomkfilter" 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>Serialized Format for BloomKFilter</h3>
<p>Serialized BloomKFilter format:</p>
<ul>
<li>1 byte for the number of hash functions.</li>
<li>1 big endian int(That is how OutputStream works) for the number of longs in the bitset</li>
<li>big endian longs in the BloomKFilter bitset</li>
</ul>
<p>Note: <code>org.apache.hive.common.util.BloomKFilter</code> provides a serialize method which can be used to serialize bloom filters to outputStream.</p>
<h3><a class="anchor" aria-hidden="true" id="filtering-sql-queries"></a><a href="#filtering-sql-queries" 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>Filtering SQL Queries</h3>
<p>Bloom filters can be used in SQL <code>WHERE</code> clauses via the <code>bloom_filter_test</code> operator:</p>
<pre><code class="hljs css language-sql"><span class="hljs-keyword">SELECT</span> <span class="hljs-keyword">COUNT</span>(*) <span class="hljs-keyword">FROM</span> druid.foo <span class="hljs-keyword">WHERE</span> bloom_filter_test(&lt;expr&gt;, <span class="hljs-string">'&lt;serialized_bytes_for_BloomKFilter&gt;'</span>)
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="expression-and-virtual-column-support"></a><a href="#expression-and-virtual-column-support" 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>Expression and Virtual Column Support</h3>
<p>The bloom filter extension also adds a bloom filter <a href="/docs/0.16.1-incubating/misc/math-expr.html">Druid expression</a> which shares syntax
with the SQL operator.</p>
<pre><code class="hljs css language-sql">bloom_filter_test(&lt;expr&gt;, '&lt;serialized_bytes_for_BloomKFilter&gt;')
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="bloom-filter-query-aggregator"></a><a href="#bloom-filter-query-aggregator" 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>Bloom Filter Query Aggregator</h2>
<p>Input for a <code>bloomKFilter</code> can also be created from a druid query with the <code>bloom</code> aggregator. Note that it is very
important to set a reasonable value for the <code>maxNumEntries</code> parameter, which is the maximum number of distinct entries
that the bloom filter can represent without increasing the false positive rate. It may be worth performing a query using
one of the unique count sketches to calculate the value for this parameter in order to build a bloom filter appropriate
for the query.</p>
<h3><a class="anchor" aria-hidden="true" id="json-specification-of-bloom-filter-aggregator"></a><a href="#json-specification-of-bloom-filter-aggregator" 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>JSON Specification of Bloom Filter Aggregator</h3>
<pre><code class="hljs css language-json">{
      <span class="hljs-attr">"type"</span>: <span class="hljs-string">"bloom"</span>,
      <span class="hljs-attr">"name"</span>: &lt;output_field_name&gt;,
      <span class="hljs-attr">"maxNumEntries"</span>: &lt;maximum_number_of_elements_for_BloomKFilter&gt;
      <span class="hljs-string">"field"</span>: &lt;dimension_spec&gt;
    }
</code></pre>
<table>
<thead>
<tr><th>Property</th><th>Description</th><th>required?</th></tr>
</thead>
<tbody>
<tr><td><code>type</code></td><td>Aggregator Type. Should always be <code>bloom</code></td><td>yes</td></tr>
<tr><td><code>name</code></td><td>Output field name</td><td>yes</td></tr>
<tr><td><code>field</code></td><td><a href="/docs/0.16.1-incubating/querying/dimensionspecs.html">DimensionSpec</a> to add to <code>org.apache.hive.common.util.BloomKFilter</code></td><td>yes</td></tr>
<tr><td><code>maxNumEntries</code></td><td>Maximum number of distinct values supported by <code>org.apache.hive.common.util.BloomKFilter</code>, default <code>1500</code></td><td>no</td></tr>
</tbody>
</table>
<h3><a class="anchor" aria-hidden="true" id="example"></a><a href="#example" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example</h3>
<pre><code class="hljs css language-json">{
  <span class="hljs-attr">"queryType"</span>: <span class="hljs-string">"timeseries"</span>,
  <span class="hljs-attr">"dataSource"</span>: <span class="hljs-string">"wikiticker"</span>,
  <span class="hljs-attr">"intervals"</span>: [ <span class="hljs-string">"2015-09-12T00:00:00.000/2015-09-13T00:00:00.000"</span> ],
  <span class="hljs-attr">"granularity"</span>: <span class="hljs-string">"day"</span>,
  <span class="hljs-attr">"aggregations"</span>: [
    {
      <span class="hljs-attr">"type"</span>: <span class="hljs-string">"bloom"</span>,
      <span class="hljs-attr">"name"</span>: <span class="hljs-string">"userBloom"</span>,
      <span class="hljs-attr">"maxNumEntries"</span>: <span class="hljs-number">100000</span>,
      <span class="hljs-attr">"field"</span>: {
        <span class="hljs-attr">"type"</span>:<span class="hljs-string">"default"</span>,
        <span class="hljs-attr">"dimension"</span>:<span class="hljs-string">"user"</span>,
        <span class="hljs-attr">"outputType"</span>: <span class="hljs-string">"STRING"</span>
      }
    }
  ]
}
</code></pre>
<p>response</p>
<pre><code class="hljs css language-json">[{<span class="hljs-attr">"timestamp"</span>:<span class="hljs-string">"2015-09-12T00:00:00.000Z"</span>,<span class="hljs-attr">"result"</span>:{<span class="hljs-attr">"userBloom"</span>:<span class="hljs-string">"BAAAJhAAAA..."</span>}}]
</code></pre>
<p>These values can then be set in the filter specification described above.</p>
<p>Ordering results by a bloom filter aggregator, for example in a TopN query, will perform a comparatively expensive
linear scan <em>of the filter itself</em> to count the number of set bits as a means of approximating how many items have been
added to the set. As such, ordering by an alternate aggregation is recommended if possible.</p>
<h3><a class="anchor" aria-hidden="true" id="sql-bloom-filter-aggregator"></a><a href="#sql-bloom-filter-aggregator" 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>SQL Bloom Filter Aggregator</h3>
<p>Bloom filters can be computed in SQL expressions with the <code>bloom_filter</code> aggregator:</p>
<pre><code class="hljs css language-sql"><span class="hljs-keyword">SELECT</span> BLOOM_FILTER(&lt;expression&gt;, &lt;<span class="hljs-keyword">max</span> <span class="hljs-built_in">number</span> <span class="hljs-keyword">of</span> entries&gt;) <span class="hljs-keyword">FROM</span> druid.foo <span class="hljs-keyword">WHERE</span> dim2 = <span class="hljs-string">'abc'</span>
</code></pre>
<p>but requires the setting <code>druid.sql.planner.serializeComplexValues</code> to be set to <code>true</code>. Bloom filter results in an SQL
response are serialized into a base64 string, which can then be used in subsequent queries as a filter.</p>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/0.16.1-incubating/development/extensions-core/avro.html"><span class="arrow-prev">← </span><span>Apache Avro</span></a><a class="docs-next button" href="/docs/0.16.1-incubating/development/extensions-core/datasketches-extension.html"><span class="function-name-prevnext">DataSketches extension</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#filtering-queries-with-a-bloom-filter">Filtering queries with a Bloom Filter</a><ul class="toc-headings"><li><a href="#json-specification-of-bloom-filter">JSON Specification of Bloom Filter</a></li><li><a href="#serialized-format-for-bloomkfilter">Serialized Format for BloomKFilter</a></li><li><a href="#filtering-sql-queries">Filtering SQL Queries</a></li><li><a href="#expression-and-virtual-column-support">Expression and Virtual Column Support</a></li></ul></li><li><a href="#bloom-filter-query-aggregator">Bloom Filter Query Aggregator</a><ul class="toc-headings"><li><a href="#json-specification-of-bloom-filter-aggregator">JSON Specification of Bloom Filter Aggregator</a></li><li><a href="#example">Example</a></li><li><a href="#sql-bloom-filter-aggregator">SQL Bloom Filter Aggregator</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>