| <html lang="en" dir="ltr" class="docs-wrapper docs-doc-page docs-version-current plugin-docs plugin-id-default docs-doc-id-design/historical"> |
| <meta name="generator" content="Docusaurus v2.4.1"> |
| <title data-rh="true">Historical Process | 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/latest/design/historical"><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="Historical Process | 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/latest/design/historical"><link data-rh="true" rel="alternate" href="https://druid.apache.org/docs/latest/design/historical" hreflang="en"><link data-rh="true" rel="alternate" href="https://druid.apache.org/docs/latest/design/historical" 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.546f39eb.css"> |
| <link rel="preload" href="/assets/js/runtime~main.4c9a7172.js" as="script"> |
| <link rel="preload" href="/assets/js/main.3a5ab01b.js" as="script"> |
| <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 aria-current="page" class="navbar__item navbar__link navbar__link--active" href="/docs/latest/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"><main class="docMainContainer_gTbr docMainContainerEnhanced_Uz_u"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><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>Historical Process</h1></header><h3 class="anchor anchorWithStickyNavbar_LWe7" id="configuration">Configuration<a href="#configuration" class="hash-link" aria-label="Direct link to Configuration" title="Direct link to Configuration"></a></h3><p>For Apache Druid Historical Process Configuration, see <a href="/docs/latest/configuration/#historical">Historical Configuration</a>.</p><p>For basic tuning guidance for the Historical process, see <a href="/docs/latest/operations/basic-cluster-tuning#historical">Basic cluster tuning</a>.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="http-endpoints">HTTP endpoints<a href="#http-endpoints" class="hash-link" aria-label="Direct link to HTTP endpoints" title="Direct link to HTTP endpoints"></a></h3><p>For a list of API endpoints supported by the Historical, please see the <a href="/docs/latest/api-reference/service-status-api#historical">Service status API reference</a>.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="running">Running<a href="#running" class="hash-link" aria-label="Direct link to Running" title="Direct link to Running"></a></h3><div class="codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-text codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token plain">org.apache.druid.cli.Main server historical</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h3 class="anchor anchorWithStickyNavbar_LWe7" id="loading-and-serving-segments">Loading and serving segments<a href="#loading-and-serving-segments" class="hash-link" aria-label="Direct link to Loading and serving segments" title="Direct link to Loading and serving segments"></a></h3><p>Each Historical process copies or "pulls" segment files from Deep Storage to local disk in an area called the <em>segment cache</em>. Set the <code>druid.segmentCache.locations</code> to configure the size and location of the segment cache on each Historical process. See <a href="/docs/latest/configuration/#historical-general-configuration">Historical general configuration</a>.</p><p>See the <a href="/docs/latest/operations/basic-cluster-tuning#segment-cache-size">Tuning Guide</a> for more information.</p><p>The <a href="/docs/latest/design/coordinator">Coordinator</a> controls the assignment of segments to Historicals and the balance of segments between Historicals. Historical processes do not communicate directly with each other, nor do they communicate directly with the Coordinator. Instead, the Coordinator creates ephemeral entries in Zookeeper in a <a href="/docs/latest/configuration/#path-configuration">load queue path</a>. Each Historical process maintains a connection to Zookeeper, watching those paths for segment information.</p><p>For more information about how the Coordinator assigns segments to Historical processes, see <a href="/docs/latest/design/coordinator">Coordinator</a>.</p><p>When a Historical process detects a new entry in the Zookeeper load queue, it checks its own segment cache. If no information about the segment exists there, the Historical process first retrieves metadata from Zookeeper about the segment, including where the segment is located in Deep Storage and how it needs to decompress and process it.</p><p>For more information about segment metadata and Druid segments in general, see <a href="/docs/latest/design/segments">Segments</a>. </p><p>After a Historical process pulls down and processes a segment from Deep Storage, Druid advertises the segment as being available for queries from the Broker. This announcement by the Historical is made via Zookeeper, in a <a href="/docs/latest/configuration/#path-configuration">served segments path</a>.</p><p>For more information about how the Broker determines what data is available for queries, please see <a href="/docs/latest/design/broker">Broker</a>.</p><p>To make data from the segment cache available for querying as soon as possible, Historical services search the local segment cache upon startup and advertise the segments found there.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="loading-and-serving-segments-from-cache">Loading and serving segments from cache<a href="#loading-and-serving-segments-from-cache" class="hash-link" aria-label="Direct link to Loading and serving segments from cache" title="Direct link to Loading and serving segments from cache"></a></h3><p>The segment cache uses <a href="https://en.wikipedia.org/wiki/Mmap" target="_blank" rel="noopener noreferrer">memory mapping</a>. The cache consumes memory from the underlying operating system so Historicals can hold parts of segment files in memory to increase query performance at the data level. The in-memory segment cache is affected by the size of the Historical JVM, heap / direct memory buffers, and other processes on the operating system itself.</p><p>At query time, if the required part of a segment file is available in the memory mapped cache or "page cache", the Historical re-uses it and reads it directly from memory. If it is not in the memory-mapped cache, the Historical reads that part of the segment from disk. In this case, there is potential for new data to flush other segment data from memory. This means that if free operating system memory is close to <code>druid.server.maxSize</code>, the more likely that segment data will be available in memory and reduce query times. Conversely, the lower the free operating system memory, the more likely a Historical is to read segments from disk.</p><p>Note that this memory-mapped segment cache is in addition to other <a href="/docs/latest/querying/caching">query-level caches</a>.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="querying-segments">Querying segments<a href="#querying-segments" class="hash-link" aria-label="Direct link to Querying segments" title="Direct link to Querying segments"></a></h3><p>Please see <a href="/docs/latest/querying/">Querying</a> for more information on querying Historical processes.</p><p>A Historical can be configured to log and report metrics for every query it services.</p></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"></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="#configuration" class="table-of-contents__link toc-highlight">Configuration</a></li><li><a href="#http-endpoints" class="table-of-contents__link toc-highlight">HTTP endpoints</a></li><li><a href="#running" class="table-of-contents__link toc-highlight">Running</a></li><li><a href="#loading-and-serving-segments" class="table-of-contents__link toc-highlight">Loading and serving segments</a></li><li><a href="#loading-and-serving-segments-from-cache" class="table-of-contents__link toc-highlight">Loading and serving segments from cache</a></li><li><a href="#querying-segments" class="table-of-contents__link toc-highlight">Querying segments</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.4c9a7172.js"></script> |
| <script src="/assets/js/main.3a5ab01b.js"></script> |
