| <!DOCTYPE html> |
| <html lang="en"> |
| <head> |
| <meta charset="UTF-8" /> |
| <meta name="viewport" content="width=device-width, initial-scale=1.0"> |
| <meta name="description" content="Apache Druid"> |
| <meta name="keywords" content="druid,kafka,database,analytics,streaming,real-time,real time,apache,open source"> |
| <meta name="author" content="Apache Software Foundation"> |
| |
| <title>Druid | Developing on Apache Druid (incubating)</title> |
| |
| <link rel="alternate" type="application/atom+xml" href="/feed"> |
| <link rel="shortcut icon" href="/img/favicon.png"> |
| |
| <link rel="stylesheet" href="/assets/css/font-awesome-5.css"> |
| |
| <link href='//fonts.googleapis.com/css?family=Open+Sans+Condensed:300,700,300italic|Open+Sans:300italic,400italic,600italic,400,300,600,700' rel='stylesheet' type='text/css'> |
| |
| <link rel="stylesheet" href="/css/bootstrap-pure.css?v=1.1"> |
| <link rel="stylesheet" href="/css/base.css?v=1.1"> |
| <link rel="stylesheet" href="/css/header.css?v=1.1"> |
| <link rel="stylesheet" href="/css/footer.css?v=1.1"> |
| <link rel="stylesheet" href="/css/syntax.css?v=1.1"> |
| <link rel="stylesheet" href="/css/docs.css?v=1.1"> |
| |
| <script> |
| (function() { |
| var cx = '000162378814775985090:molvbm0vggm'; |
| var gcse = document.createElement('script'); |
| gcse.type = 'text/javascript'; |
| gcse.async = true; |
| gcse.src = (document.location.protocol == 'https:' ? 'https:' : 'http:') + |
| '//cse.google.com/cse.js?cx=' + cx; |
| var s = document.getElementsByTagName('script')[0]; |
| s.parentNode.insertBefore(gcse, s); |
| })(); |
| </script> |
| |
| |
| </head> |
| |
| <body> |
| <!-- Start page_header include --> |
| <script src="//ajax.googleapis.com/ajax/libs/jquery/2.2.4/jquery.min.js"></script> |
| |
| <div class="top-navigator"> |
| <div class="container"> |
| <div class="left-cont"> |
| <a class="logo" href="/"><span class="druid-logo"></span></a> |
| </div> |
| <div class="right-cont"> |
| <ul class="links"> |
| <li class=""><a href="/technology">Technology</a></li> |
| <li class=""><a href="/use-cases">Use Cases</a></li> |
| <li class=""><a href="/druid-powered">Powered By</a></li> |
| <li class=""><a href="/docs/latest/design/">Docs</a></li> |
| <li class=""><a href="/community/">Community</a></li> |
| <li class="header-dropdown"> |
| <a>Apache</a> |
| <div class="header-dropdown-menu"> |
| <a href="https://www.apache.org/" target="_blank">Foundation</a> |
| <a href="https://www.apache.org/events/current-event" target="_blank">Events</a> |
| <a href="https://www.apache.org/licenses/" target="_blank">License</a> |
| <a href="https://www.apache.org/foundation/thanks.html" target="_blank">Thanks</a> |
| <a href="https://www.apache.org/security/" target="_blank">Security</a> |
| <a href="https://www.apache.org/foundation/sponsorship.html" target="_blank">Sponsorship</a> |
| </div> |
| </li> |
| <li class=" button-link"><a href="/downloads.html">Download</a></li> |
| </ul> |
| </div> |
| </div> |
| <div class="action-button menu-icon"> |
| <span class="fa fa-bars"></span> MENU |
| </div> |
| <div class="action-button menu-icon-close"> |
| <span class="fa fa-times"></span> MENU |
| </div> |
| </div> |
| |
| <script type="text/javascript"> |
| var $menu = $('.right-cont'); |
| var $menuIcon = $('.menu-icon'); |
| var $menuIconClose = $('.menu-icon-close'); |
| |
| function showMenu() { |
| $menu.fadeIn(100); |
| $menuIcon.fadeOut(100); |
| $menuIconClose.fadeIn(100); |
| } |
| |
| $menuIcon.click(showMenu); |
| |
| function hideMenu() { |
| $menu.fadeOut(100); |
| $menuIconClose.fadeOut(100); |
| $menuIcon.fadeIn(100); |
| } |
| |
| $menuIconClose.click(hideMenu); |
| |
| $(window).resize(function() { |
| if ($(window).width() >= 840) { |
| $menu.fadeIn(100); |
| $menuIcon.fadeOut(100); |
| $menuIconClose.fadeOut(100); |
| } |
| else { |
| $menu.fadeOut(100); |
| $menuIcon.fadeIn(100); |
| $menuIconClose.fadeOut(100); |
| } |
| }); |
| </script> |
| |
| <!-- Stop page_header include --> |
| |
| |
| <div class="container doc-container"> |
| |
| |
| |
| |
| <p> Looking for the <a href="/docs/26.0.0/">latest stable documentation</a>?</p> |
| |
| |
| <div class="row"> |
| <div class="col-md-9 doc-content"> |
| <p> |
| <a class="btn btn-default btn-xs visible-xs-inline-block visible-sm-inline-block" href="#toc">Table of Contents</a> |
| </p> |
| <!-- |
| ~ 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. |
| --> |
| |
| <h1 id="developing-on-apache-druid-incubating">Developing on Apache Druid (incubating)</h1> |
| |
| <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 id="storage-format">Storage Format</h2> |
| |
| <p>Data in Druid is stored in a custom column format known as a <a href="../design/segments.html">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 id="segment-creation">Segment Creation</h2> |
| |
| <p>Raw data is ingested in <code>IncrementalIndex.java</code>, and segments are created in <code>IndexMerger.java</code>.</p> |
| |
| <h2 id="storage-engine">Storage Engine</h2> |
| |
| <p>Druid segments are memory mapped in <code>IndexIO.java</code> to be exposed for querying.</p> |
| |
| <h2 id="query-engine">Query Engine</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 id="coordination">Coordination</h2> |
| |
| <p>Most of the coordination logic for Historical processes is on the Druid Coordinator. The starting point here is <code>DruidCoordinator.java</code>.<br> |
| 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 id="real-time-ingestion">Real-time Ingestion</h2> |
| |
| <p>Druid loads data through <code>FirehoseFactory.java</code> classes. Firehoses often wrap other firehoses, where, similar to the design of the<br> |
| query runners, each firehose adds a layer of logic. Much of the core management logic is in <code>RealtimeManager.java</code> and the |
| persist and hand-off logic is in <code>RealtimePlumber.java</code>.</p> |
| |
| <h2 id="hadoop-based-batch-ingestion">Hadoop-based Batch Ingestion</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 id="internal-uis">Internal UIs</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 id="client-libraries">Client Libraries</h2> |
| |
| <p>We welcome contributions for new client libraries to interact with Druid. See client |
| <a href="/libraries.html">libraries</a> for existing client libraries.</p> |
| |
| </div> |
| <div class="col-md-3"> |
| <div class="searchbox"> |
| <gcse:searchbox-only></gcse:searchbox-only> |
| </div> |
| <div id="toc" class="nav toc hidden-print"> |
| </div> |
| </div> |
| </div> |
| </div> |
| |
| <!-- Start page_footer include --> |
| <footer class="druid-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/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="GitHub" href="https://github.com/apache/druid" target="_blank"><span class="fab fa-github"></span></a> |
| </div> |
| <div class="text-center license"> |
| Copyright © 2020 <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> |
| |
| <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> |
| <script> |
| function trackDownload(type, url) { |
| ga('send', 'event', 'download', type, url); |
| } |
| </script> |
| <script src="//code.jquery.com/jquery.min.js"></script> |
| <script src="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script> |
| <script src="/assets/js/druid.js"></script> |
| <!-- stop page_footer include --> |
| |
| |
| <script> |
| $(function() { |
| $(".toc").load("/docs/0.15.0-incubating/toc.html"); |
| |
| // There is no way to tell when .gsc-input will be async loaded into the page so just try to set a placeholder until it works |
| var tries = 0; |
| var timer = setInterval(function() { |
| tries++; |
| if (tries > 300) clearInterval(timer); |
| var searchInput = $('input.gsc-input'); |
| if (searchInput.length) { |
| searchInput.attr('placeholder', 'Search'); |
| clearInterval(timer); |
| } |
| }, 100); |
| }); |
| </script> |
| </body> |
| </html> |
