| <!doctype html> |
| <html lang="en" dir="ltr" class="docs-wrapper docs-doc-page docs-version-current plugin-docs plugin-id-default docs-doc-id-development/overview"> |
| <head> |
| <meta charset="UTF-8"> |
| <meta name="generator" content="Docusaurus v2.4.1"> |
| <title data-rh="true">Developing on Apache Druid | Apache® Druid</title><meta data-rh="true" name="viewport" content="width=device-width,initial-scale=1"><meta data-rh="true" name="twitter:card" content="summary_large_image"><meta data-rh="true" property="og:image" content="https://druid.apache.org/img/druid_nav.png"><meta data-rh="true" name="twitter:image" content="https://druid.apache.org/img/druid_nav.png"><meta data-rh="true" property="og:url" content="https://druid.apache.org/docs/27.0.0/development/overview"><meta data-rh="true" name="docusaurus_locale" content="en"><meta data-rh="true" name="docsearch:language" content="en"><meta data-rh="true" name="docusaurus_version" content="current"><meta data-rh="true" name="docusaurus_tag" content="docs-default-current"><meta data-rh="true" name="docsearch:version" content="current"><meta data-rh="true" name="docsearch:docusaurus_tag" content="docs-default-current"><meta data-rh="true" property="og:title" content="Developing on Apache Druid | Apache® Druid"><meta data-rh="true" name="description" content="<!--"><meta data-rh="true" property="og:description" content="<!--"><link data-rh="true" rel="icon" href="/img/favicon.png"><link data-rh="true" rel="canonical" href="https://druid.apache.org/docs/27.0.0/development/overview"><link data-rh="true" rel="alternate" href="https://druid.apache.org/docs/27.0.0/development/overview" hreflang="en"><link data-rh="true" rel="alternate" href="https://druid.apache.org/docs/27.0.0/development/overview" hreflang="x-default"><link rel="preconnect" href="https://www.google-analytics.com"> |
| <link rel="preconnect" href="https://www.googletagmanager.com"> |
| <script async src="https://www.googletagmanager.com/gtag/js?id=UA-131010415-1"></script> |
| <script>function gtag(){dataLayer.push(arguments)}window.dataLayer=window.dataLayer||[],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"> |
| <script src="https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.4/clipboard.min.js"></script><link rel="stylesheet" href="/assets/css/styles.f80751b3.css"> |
| <link rel="preload" href="/assets/js/runtime~main.5371e784.js" as="script"> |
| <link rel="preload" href="/assets/js/main.832012d1.js" as="script"> |
| </head> |
| <body class="navigation-with-keyboard"> |
| <script>!function(){function t(t){document.documentElement.setAttribute("data-theme",t)}var e=function(){var t=null;try{t=new URLSearchParams(window.location.search).get("docusaurus-theme")}catch(t){}return t}()||function(){var t=null;try{t=localStorage.getItem("theme")}catch(t){}return t}();t(null!==e?e:"light")}()</script><div id="__docusaurus"> |
| <div role="region" aria-label="Skip to main content"><a class="skipToContent_fXgn" href="#__docusaurus_skipToContent_fallback">Skip to main content</a></div><nav aria-label="Main" class="navbar navbar--fixed-top navbar--dark"><div class="navbar__inner"><div class="navbar__items"><button aria-label="Toggle navigation bar" aria-expanded="false" class="navbar__toggle clean-btn" type="button"><svg width="30" height="30" viewBox="0 0 30 30" aria-hidden="true"><path stroke="currentColor" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2" d="M4 7h22M4 15h22M4 23h22"></path></svg></button><a class="navbar__brand" href="/"><div class="navbar__logo"><img src="/img/druid_nav.png" alt="Apache® Druid" class="themedImage_ToTc themedImage--light_HNdA"><img src="/img/druid_nav.png" alt="Apache® Druid" class="themedImage_ToTc themedImage--dark_i4oU"></div></a></div><div class="navbar__items navbar__items--right"><a class="navbar__item navbar__link" href="/technology">Technology</a><a class="navbar__item navbar__link" href="/use-cases">Use Cases</a><a class="navbar__item navbar__link" href="/druid-powered">Powered By</a><a class="navbar__item navbar__link" href="/docs/27.0.0/design/">Docs</a><a class="navbar__item navbar__link" href="/community/">Community</a><div class="navbar__item dropdown dropdown--hoverable dropdown--right"><a href="#" aria-haspopup="true" aria-expanded="false" role="button" class="navbar__link">Apache®</a><ul class="dropdown__menu"><li><a href="https://www.apache.org/" target="_blank" rel="noopener noreferrer" class="dropdown__link">Foundation<svg width="12" height="12" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li><a href="https://apachecon.com/?ref=druid.apache.org" target="_blank" rel="noopener noreferrer" class="dropdown__link">Events<svg width="12" height="12" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li><a href="https://www.apache.org/licenses/" target="_blank" rel="noopener noreferrer" class="dropdown__link">License<svg width="12" height="12" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li><a href="https://www.apache.org/foundation/thanks.html" target="_blank" rel="noopener noreferrer" class="dropdown__link">Thanks<svg width="12" height="12" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li><a href="https://www.apache.org/security/" target="_blank" rel="noopener noreferrer" class="dropdown__link">Security<svg width="12" height="12" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li><a href="https://www.apache.org/foundation/sponsorship.html" target="_blank" rel="noopener noreferrer" class="dropdown__link">Sponsorship<svg width="12" height="12" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li></ul></div><a class="navbar__item navbar__link" href="/downloads/">Download</a><div class="searchBox_ZlJk"><div class="navbar__search"><span aria-label="expand searchbar" role="button" class="search-icon" tabindex="0"></span><input type="search" id="search_input_react" placeholder="Loading..." aria-label="Search" class="navbar__search-input search-bar" disabled=""></div></div></div></div><div role="presentation" class="navbar-sidebar__backdrop"></div></nav><div id="__docusaurus_skipToContent_fallback" class="main-wrapper mainWrapper_z2l0 docsWrapper_BCFX"><button aria-label="Scroll back to top" class="clean-btn theme-back-to-top-button backToTopButton_sjWU" type="button"></button><div class="docPage__5DB"><aside class="theme-doc-sidebar-container docSidebarContainer_b6E3"><div class="sidebarViewport_Xe31"><div class="sidebar_njMd"><nav aria-label="Docs sidebar" class="menu thin-scrollbar menu_SIkG"><ul class="theme-doc-sidebar-menu menu__list"><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/design/">Getting started</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/tutorials/tutorial-msq-extern">Tutorials</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/design/architecture">Design</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/ingestion/">Ingestion</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/data-management/">Data management</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/querying/sql">Querying</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/api-reference/">API reference</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/configuration/">Configuration</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/operations/web-console">Operations</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" aria-expanded="true" href="/docs/27.0.0/development/overview">Development</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="/docs/27.0.0/development/overview">Developing on Druid</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/27.0.0/development/modules">Creating extensions</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/27.0.0/development/javascript">JavaScript functionality</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/27.0.0/development/build">Build from source</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/27.0.0/development/versioning">Versioning</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/27.0.0/development/contribute-to-docs">Contribute to Druid docs</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/27.0.0/development/experimental">Experimental features</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/27.0.0/misc/papers-and-talks">Misc</a></div></li></ul></nav></div></div></aside><main class="docMainContainer_gTbr"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label="Breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="/"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Development</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Developing on Druid</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Developing on Apache Druid</h1></header><p>Druid's codebase consists of several major components. For developers interested in learning the code, this document provides |
| a high level overview of the main components that make up Druid and the relevant classes to start from to learn the code.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="storage-format">Storage format<a href="#storage-format" class="hash-link" aria-label="Direct link to Storage format" title="Direct link to Storage format"></a></h2><p>Data in Druid is stored in a custom column format known as a <a href="/docs/27.0.0/design/segments">segment</a>. Segments are composed of |
| different types of columns. <code>Column.java</code> and the classes that extend it is a great place to looking into the storage format.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="segment-creation">Segment creation<a href="#segment-creation" class="hash-link" aria-label="Direct link to Segment creation" title="Direct link to Segment creation"></a></h2><p>Raw data is ingested in <code>IncrementalIndex.java</code>, and segments are created in <code>IndexMerger.java</code>.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="storage-engine">Storage engine<a href="#storage-engine" class="hash-link" aria-label="Direct link to Storage engine" title="Direct link to Storage engine"></a></h2><p>Druid segments are memory mapped in <code>IndexIO.java</code> to be exposed for querying.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="query-engine">Query engine<a href="#query-engine" class="hash-link" aria-label="Direct link to Query engine" title="Direct link to Query engine"></a></h2><p>Most of the logic related to Druid queries can be found in the Query* classes. Druid leverages query runners to run queries. |
| Query runners often embed other query runners and each query runner adds on a layer of logic. A good starting point to trace |
| the query logic is to start from <code>QueryResource.java</code>.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="coordination">Coordination<a href="#coordination" class="hash-link" aria-label="Direct link to Coordination" title="Direct link to Coordination"></a></h2><p>Most of the coordination logic for Historical processes is on the Druid Coordinator. The starting point here is <code>DruidCoordinator.java</code>. |
| Most of the coordination logic for (real-time) ingestion is in the Druid indexing service. The starting point here is <code>OverlordResource.java</code>.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="real-time-ingestion">Real-time Ingestion<a href="#real-time-ingestion" class="hash-link" aria-label="Direct link to Real-time Ingestion" title="Direct link to Real-time Ingestion"></a></h2><p>Druid loads data through <code>FirehoseFactory.java</code> classes. Firehoses often wrap other firehoses, where, similar to the design of the |
| query runners, each firehose adds a layer of logic, and the persist and hand-off logic is in <code>RealtimePlumber.java</code>.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="hadoop-based-batch-ingestion">Hadoop-based Batch Ingestion<a href="#hadoop-based-batch-ingestion" class="hash-link" aria-label="Direct link to Hadoop-based Batch Ingestion" title="Direct link to Hadoop-based Batch Ingestion"></a></h2><p>The two main Hadoop indexing classes are <code>HadoopDruidDetermineConfigurationJob.java</code> for the job to determine how many Druid |
| segments to create, and <code>HadoopDruidIndexerJob.java</code>, which creates Druid segments.</p><p>At some point in the future, we may move the Hadoop ingestion code out of core Druid.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="internal-uis">Internal UIs<a href="#internal-uis" class="hash-link" aria-label="Direct link to Internal UIs" title="Direct link to Internal UIs"></a></h2><p>Druid currently has two internal UIs. One is for the Coordinator and one is for the Overlord.</p><p>At some point in the future, we will likely move the internal UI code out of core Druid.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="client-libraries">Client libraries<a href="#client-libraries" class="hash-link" aria-label="Direct link to Client libraries" title="Direct link to Client libraries"></a></h2><p>We welcome contributions for new client libraries to interact with Druid. See the |
| <a href="https://druid.apache.org/libraries.html" target="_blank" rel="noopener noreferrer">Community and third-party libraries</a> page for links to existing client |
| libraries.</p></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"><a class="pagination-nav__link pagination-nav__link--prev" href="/docs/27.0.0/operations/use_sbt_to_build_fat_jar"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Content for build.sbt</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/docs/27.0.0/development/modules"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">Creating extensions</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#storage-format" class="table-of-contents__link toc-highlight">Storage format</a></li><li><a href="#segment-creation" class="table-of-contents__link toc-highlight">Segment creation</a></li><li><a href="#storage-engine" class="table-of-contents__link toc-highlight">Storage engine</a></li><li><a href="#query-engine" class="table-of-contents__link toc-highlight">Query engine</a></li><li><a href="#coordination" class="table-of-contents__link toc-highlight">Coordination</a></li><li><a href="#real-time-ingestion" class="table-of-contents__link toc-highlight">Real-time Ingestion</a></li><li><a href="#hadoop-based-batch-ingestion" class="table-of-contents__link toc-highlight">Hadoop-based Batch Ingestion</a></li><li><a href="#internal-uis" class="table-of-contents__link toc-highlight">Internal UIs</a></li><li><a href="#client-libraries" class="table-of-contents__link toc-highlight">Client libraries</a></li></ul></div></div></div></div></main></div></div><footer class="footer"><div class="container container-fluid"><div class="footer__bottom text--center"><div class="margin-bottom--sm"><img src="/img/favicon.png" class="themedImage_ToTc themedImage--light_HNdA footer__logo"><img src="/img/favicon.png" class="themedImage_ToTc themedImage--dark_i4oU footer__logo"></div><div class="footer__copyright">Copyright © 2023 Apache Software Foundation. Except where otherwise noted, licensed under CC BY-SA 4.0. 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></div></footer></div> |
| <script src="/assets/js/runtime~main.5371e784.js"></script> |
| <script src="/assets/js/main.832012d1.js"></script> |
| </body> |
| </html> |
