docs/0.14.0-incubating/dependencies/zookeeper.html - druid-website - Git at Google

 <!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 | ZooKeeper</title>

 <link rel="alternate" type="application/atom+xml" href="/feed">
 <link rel="shortcut icon" href="/img/favicon.png">

 <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.2/css/all.css" integrity="sha384-fnmOCqbTlWIlj8LyTjo7mOUStjsKC4pOpQbqyi7RrhN7udi9RwhKkMHpvLbHG9Sr" crossorigin="anonymous">

 <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/0.16.1-incubating/">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="zookeeper">ZooKeeper</h1>

 <p>Apache Druid (incubating) uses <a href="http://zookeeper.apache.org/">Apache ZooKeeper</a> (ZK) for management of current cluster state. The operations that happen over ZK are</p>

 <ol>
 <li> <a href="../design/coordinator.html">Coordinator</a> leader election</li>
 <li> Segment &quot;publishing&quot; protocol from <a href="../design/historical.html">Historical</a> and <a href="../design/realtime.html">Realtime</a></li>
 <li> Segment load/drop protocol between <a href="../design/coordinator.html">Coordinator</a> and <a href="../design/historical.html">Historical</a></li>
 <li> <a href="../design/overlord.html">Overlord</a> leader election</li>
 <li> <a href="../design/overlord.html">Overlord</a> and <a href="../design/middlemanager.html">MiddleManager</a> task management</li>
 </ol>

 <h3 id="coordinator-leader-election">Coordinator Leader Election</h3>

 <p>We use the Curator LeadershipLatch recipe to do leader election at path</p>
 <div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.coordinatorPath}/_COORDINATOR
 </code></pre></div>
 <h3 id="segment-publishing-protocol-from-historical-and-realtime">Segment &quot;publishing&quot; protocol from Historical and Realtime</h3>

 <p>The <code>announcementsPath</code> and <code>servedSegmentsPath</code> are used for this.</p>

 <p>All <a href="../design/historical.html">Historical</a> and <a href="../design/realtime.html">Realtime</a> processes publish themselves on the <code>announcementsPath</code>, specifically, they will create an ephemeral znode at</p>
 <div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.announcementsPath}/${druid.host}
 </code></pre></div>
 <p>Which signifies that they exist. They will also subsequently create a permanent znode at</p>
 <div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.servedSegmentsPath}/${druid.host}
 </code></pre></div>
 <p>And as they load up segments, they will attach ephemeral znodes that look like</p>
 <div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.servedSegmentsPath}/${druid.host}/_segment_identifier_
 </code></pre></div>
 <p>Processes like the <a href="../design/coordinator.html">Coordinator</a> and <a href="../design/broker.html">Broker</a> can then watch these paths to see which processes are currently serving which segments.</p>

 <h3 id="segment-load-drop-protocol-between-coordinator-and-historical">Segment load/drop protocol between Coordinator and Historical</h3>

 <p>The <code>loadQueuePath</code> is used for this.</p>

 <p>When the <a href="../design/coordinator.html">Coordinator</a> decides that a <a href="../design/historical.html">Historical</a> process should load or drop a segment, it writes an ephemeral znode to</p>
 <div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.loadQueuePath}/_host_of_historical_process/_segment_identifier
 </code></pre></div>
 <p>This znode will contain a payload that indicates to the Historical process what it should do with the given segment. When the Historical process is done with the work, it will delete the znode in order to signify to the Coordinator that it is complete.</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>&ensp;·&ensp;
     <a href="/use-cases">Use Cases</a>&ensp;·&ensp;
     <a href="/druid-powered">Powered by Druid</a>&ensp;·&ensp;
     <a href="/docs/latest">Docs</a>&ensp;·&ensp;
     <a href="/community/">Community</a>&ensp;·&ensp;
     <a href="/downloads.html">Download</a>&ensp;·&ensp;
     <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>&ensp;·&ensp;
     <a title="Follow Druid" href="https://twitter.com/druidio" target="_blank"><span class="fab fa-twitter"></span></a>&ensp;·&ensp;
     <a title="Download via Apache" href="https://www.apache.org/dyn/closer.cgi?path=/incubator/druid/0.16.1-incubating/apache-druid-0.16.1-incubating-bin.tar.gz" target="_blank"><span class="fas fa-feather"></span></a>&ensp;·&ensp;
     <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>

 <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/0.14.0-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>
	<!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 \| ZooKeeper</title>

	<link rel="alternate" type="application/atom+xml" href="/feed">
	<link rel="shortcut icon" href="/img/favicon.png">

	<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.2/css/all.css" integrity="sha384-fnmOCqbTlWIlj8LyTjo7mOUStjsKC4pOpQbqyi7RrhN7udi9RwhKkMHpvLbHG9Sr" crossorigin="anonymous">

	<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/0.16.1-incubating/">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="zookeeper">ZooKeeper</h1>

	<p>Apache Druid (incubating) uses <a href="http://zookeeper.apache.org/">Apache ZooKeeper</a> (ZK) for management of current cluster state. The operations that happen over ZK are</p>

	<ol>
	<li> <a href="../design/coordinator.html">Coordinator</a> leader election</li>
	<li> Segment "publishing" protocol from <a href="../design/historical.html">Historical</a> and <a href="../design/realtime.html">Realtime</a></li>
	<li> Segment load/drop protocol between <a href="../design/coordinator.html">Coordinator</a> and <a href="../design/historical.html">Historical</a></li>
	<li> <a href="../design/overlord.html">Overlord</a> leader election</li>
	<li> <a href="../design/overlord.html">Overlord</a> and <a href="../design/middlemanager.html">MiddleManager</a> task management</li>
	</ol>

	<h3 id="coordinator-leader-election">Coordinator Leader Election</h3>

	<p>We use the Curator LeadershipLatch recipe to do leader election at path</p>
	<div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.coordinatorPath}/_COORDINATOR
	</code></pre></div>
	<h3 id="segment-publishing-protocol-from-historical-and-realtime">Segment "publishing" protocol from Historical and Realtime</h3>

	<p>The <code>announcementsPath</code> and <code>servedSegmentsPath</code> are used for this.</p>

	<p>All <a href="../design/historical.html">Historical</a> and <a href="../design/realtime.html">Realtime</a> processes publish themselves on the <code>announcementsPath</code>, specifically, they will create an ephemeral znode at</p>
	<div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.announcementsPath}/${druid.host}
	</code></pre></div>
	<p>Which signifies that they exist. They will also subsequently create a permanent znode at</p>
	<div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.servedSegmentsPath}/${druid.host}
	</code></pre></div>
	<p>And as they load up segments, they will attach ephemeral znodes that look like</p>
	<div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.servedSegmentsPath}/${druid.host}/_segment_identifier_
	</code></pre></div>
	<p>Processes like the <a href="../design/coordinator.html">Coordinator</a> and <a href="../design/broker.html">Broker</a> can then watch these paths to see which processes are currently serving which segments.</p>

	<h3 id="segment-load-drop-protocol-between-coordinator-and-historical">Segment load/drop protocol between Coordinator and Historical</h3>

	<p>The <code>loadQueuePath</code> is used for this.</p>

	<p>When the <a href="../design/coordinator.html">Coordinator</a> decides that a <a href="../design/historical.html">Historical</a> process should load or drop a segment, it writes an ephemeral znode to</p>
	<div class="highlight"><pre><code class="language-text" data-lang="text"><span></span>${druid.zk.paths.loadQueuePath}/_host_of_historical_process/_segment_identifier
	</code></pre></div>
	<p>This znode will contain a payload that indicates to the Historical process what it should do with the given segment. When the Historical process is done with the work, it will delete the znode in order to signify to the Coordinator that it is complete.</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>&ensp;·&ensp;
	<a href="/use-cases">Use Cases</a>&ensp;·&ensp;
	<a href="/druid-powered">Powered by Druid</a>&ensp;·&ensp;
	<a href="/docs/latest">Docs</a>&ensp;·&ensp;
	<a href="/community/">Community</a>&ensp;·&ensp;
	<a href="/downloads.html">Download</a>&ensp;·&ensp;
	<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>&ensp;·&ensp;
	<a title="Follow Druid" href="https://twitter.com/druidio" target="_blank"><span class="fab fa-twitter"></span></a>&ensp;·&ensp;
	<a title="Download via Apache" href="https://www.apache.org/dyn/closer.cgi?path=/incubator/druid/0.16.1-incubating/apache-druid-0.16.1-incubating-bin.tar.gz" target="_blank"><span class="fas fa-feather"></span></a>&ensp;·&ensp;
	<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>

	<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/0.14.0-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>