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Added: websites/staging/zookeeper/trunk/content/doc/r3.4.7/zookeeperAdmin.html ============================================================================== --- websites/staging/zookeeper/trunk/content/doc/r3.4.7/zookeeperAdmin.html (added) +++ websites/staging/zookeeper/trunk/content/doc/r3.4.7/zookeeperAdmin.html Thu Dec 3 04:30:43 2015 @@ -0,0 +1,1898 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd";> +<html> +<head> +<META http-equiv="Content-Type" content="text/html; charset=UTF-8"> +<meta content="Apache Forrest" name="Generator"> +<meta name="Forrest-version" content="0.9"> +<meta name="Forrest-skin-name" content="pelt"> +<title>ZooKeeper Administrator's Guide</title> +<link type="text/css" href="skin/basic.css" rel="stylesheet"> +<link media="screen" type="text/css" href="skin/screen.css" rel="stylesheet"> +<link media="print" type="text/css" href="skin/print.css" rel="stylesheet"> +<link type="text/css" href="skin/profile.css" rel="stylesheet"> +<script src="skin/getBlank.js" language="javascript" type="text/javascript"></script><script src="skin/getMenu.js" language="javascript" type="text/javascript"></script><script src="skin/fontsize.js" language="javascript" type="text/javascript"></script> +<link rel="shortcut icon" href="images/favicon.ico"> +</head> +<body onload="init()"> +<script type="text/javascript">ndeSetTextSize();</script> +<div id="top"> +<!--+ + |breadtrail + +--> +<div class="breadtrail"> +<a href="http://www.apache.org/";>Apache</a> > <a href="http://zookeeper.apache.org/";>ZooKeeper</a> > <a href="http://zookeeper.apache.org/";>ZooKeeper</a><script src="skin/breadcrumbs.js" language="JavaScript" type="text/javascript"></script> +</div> +<!--+ + |header + +--> +<div class="header"> +<!--+ + |start group logo + +--> +<div class="grouplogo"> +<a href="http://hadoop.apache.org/";><img class="logoImage" alt="Hadoop" src="images/hadoop-logo.jpg" title="Apache Hadoop"></a> +</div> +<!--+ + |end group logo + +--> +<!--+ + |start Project Logo + +--> +<div class="projectlogo"> +<a href="http://zookeeper.apache.org/";><img class="logoImage" alt="ZooKeeper" src="images/zookeeper_small.gif" title="ZooKeeper: distributed coordination"></a> +</div> +<!--+ + |end Project Logo + +--> +<!--+ + |start Search + +--> +<div class="searchbox"> +<form action="http://www.google.com/search"; method="get" class="roundtopsmall"> +<input value="zookeeper.apache.org" name="sitesearch" type="hidden"><input onFocus="getBlank (this, 'Search the site with google');" size="25" name="q" id="query" type="text" value="Search the site with google"> + <input name="Search" value="Search" type="submit"> +</form> +</div> +<!--+ + |end search + +--> +<!--+ + |start Tabs + +--> +<ul id="tabs"> +<li> +<a class="unselected" href="http://zookeeper.apache.org/";>Project</a> +</li> +<li> +<a class="unselected" href="https://cwiki.apache.org/confluence/display/ZOOKEEPER/";>Wiki</a> +</li> +<li class="current"> +<a class="selected" href="index.html">ZooKeeper 3.4 Documentation</a> +</li> +</ul> +<!--+ + |end Tabs + +--> +</div> +</div> +<div id="main"> +<div id="publishedStrip"> +<!--+ + |start Subtabs + +--> +<div id="level2tabs"></div> +<!--+ + |end Endtabs + +--> +<script type="text/javascript"><!-- +document.write("Last Published: " + document.lastModified); +// --></script> +</div> +<!--+ + |breadtrail + +--> +<div class="breadtrail"> + + + </div> +<!--+ + |start Menu, mainarea + +--> +<!--+ + |start Menu + +--> +<div id="menu"> +<div onclick="SwitchMenu('menu_1.1', 'skin/')" id="menu_1.1Title" class="menutitle">Overview</div> +<div id="menu_1.1" class="menuitemgroup"> +<div class="menuitem"> +<a href="index.html">Welcome</a> +</div> +<div class="menuitem"> +<a href="zookeeperOver.html">Overview</a> +</div> +<div class="menuitem"> +<a href="zookeeperStarted.html">Getting Started</a> +</div> +<div class="menuitem"> +<a href="releasenotes.html">Release Notes</a> +</div> +</div> +<div onclick="SwitchMenu('menu_1.2', 'skin/')" id="menu_1.2Title" class="menutitle">Developer</div> +<div id="menu_1.2" class="menuitemgroup"> +<div class="menuitem"> +<a href="api/index.html">API Docs</a> +</div> +<div class="menuitem"> +<a href="zookeeperProgrammers.html">Programmer's Guide</a> +</div> +<div class="menuitem"> +<a href="javaExample.html">Java Example</a> +</div> +<div class="menuitem"> +<a href="zookeeperTutorial.html">Barrier and Queue Tutorial</a> +</div> +<div class="menuitem"> +<a href="recipes.html">Recipes</a> +</div> +</div> +<div onclick="SwitchMenu('menu_1.3', 'skin/')" id="menu_1.3Title" class="menutitle">BookKeeper</div> +<div id="menu_1.3" class="menuitemgroup"> +<div class="menuitem"> +<a href="bookkeeperStarted.html">Getting started</a> +</div> +<div class="menuitem"> +<a href="bookkeeperOverview.html">Overview</a> +</div> +<div class="menuitem"> +<a href="bookkeeperConfig.html">Setup guide</a> +</div> +<div class="menuitem"> +<a href="bookkeeperProgrammer.html">Programmer's guide</a> +</div> +</div> +<div onclick="SwitchMenu('menu_selected_1.4', 'skin/')" id="menu_selected_1.4Title" class="menutitle" style="background-image: url('skin/images/chapter_open.gif');">Admin & Ops</div> +<div id="menu_selected_1.4" class="selectedmenuitemgroup" style="display: block;"> +<div class="menupage"> +<div class="menupagetitle">Administrator's Guide</div> +</div> +<div class="menuitem"> +<a href="zookeeperQuotas.html">Quota Guide</a> +</div> +<div class="menuitem"> +<a href="zookeeperJMX.html">JMX</a> +</div> +<div class="menuitem"> +<a href="zookeeperObservers.html">Observers Guide</a> +</div> +</div> +<div onclick="SwitchMenu('menu_1.5', 'skin/')" id="menu_1.5Title" class="menutitle">Contributor</div> +<div id="menu_1.5" class="menuitemgroup"> +<div class="menuitem"> +<a href="zookeeperInternals.html">ZooKeeper Internals</a> +</div> +</div> +<div onclick="SwitchMenu('menu_1.6', 'skin/')" id="menu_1.6Title" class="menutitle">Miscellaneous</div> +<div id="menu_1.6" class="menuitemgroup"> +<div class="menuitem"> +<a href="https://cwiki.apache.org/confluence/display/ZOOKEEPER";>Wiki</a> +</div> +<div class="menuitem"> +<a href="https://cwiki.apache.org/confluence/display/ZOOKEEPER/FAQ";>FAQ</a> +</div> +<div class="menuitem"> +<a href="http://zookeeper.apache.org/mailing_lists.html";>Mailing Lists</a> +</div> +</div> +<div id="credit"></div> +<div id="roundbottom"> +<img style="display: none" class="corner" height="15" width="15" alt="" src="skin/images/rc-b-l-15-1body-2menu-3menu.png"></div> +<!--+ + |alternative credits + +--> +<div id="credit2"></div> +</div> +<!--+ + |end Menu + +--> +<!--+ + |start content + +--> +<div id="content"> +<div title="Portable Document Format" class="pdflink"> +<a class="dida" href="zookeeperAdmin.pdf"><img alt="PDF -icon" src="skin/images/pdfdoc.gif" class="skin"><br> + PDF</a> +</div> +<h1>ZooKeeper Administrator's Guide</h1> +<h3>A Guide to Deployment and Administration</h3> +<div id="front-matter"> +<div id="minitoc-area"> +<ul class="minitoc"> +<li> +<a href="#ch_deployment">Deployment</a> +<ul class="minitoc"> +<li> +<a href="#sc_systemReq">System Requirements</a> +<ul class="minitoc"> +<li> +<a href="#sc_supportedPlatforms">Supported Platforms</a> +</li> +<li> +<a href="#sc_requiredSoftware">Required Software </a> +</li> +</ul> +</li> +<li> +<a href="#sc_zkMulitServerSetup">Clustered (Multi-Server) Setup</a> +</li> +<li> +<a href="#sc_singleAndDevSetup">Single Server and Developer Setup</a> +</li> +</ul> +</li> +<li> +<a href="#ch_administration">Administration</a> +<ul class="minitoc"> +<li> +<a href="#sc_designing">Designing a ZooKeeper Deployment</a> +<ul class="minitoc"> +<li> +<a href="#sc_CrossMachineRequirements">Cross Machine Requirements</a> +</li> +<li> +<a href="#Single+Machine+Requirements">Single Machine Requirements</a> +</li> +</ul> +</li> +<li> +<a href="#sc_provisioning">Provisioning</a> +</li> +<li> +<a href="#sc_strengthsAndLimitations">Things to Consider: ZooKeeper Strengths and Limitations</a> +</li> +<li> +<a href="#sc_administering">Administering</a> +</li> +<li> +<a href="#sc_maintenance">Maintenance</a> +<ul class="minitoc"> +<li> +<a href="#Ongoing+Data+Directory+Cleanup">Ongoing Data Directory Cleanup</a> +</li> +<li> +<a href="#Debug+Log+Cleanup+%28log4j%29">Debug Log Cleanup (log4j)</a> +</li> +</ul> +</li> +<li> +<a href="#sc_supervision">Supervision</a> +</li> +<li> +<a href="#sc_monitoring">Monitoring</a> +</li> +<li> +<a href="#sc_logging">Logging</a> +</li> +<li> +<a href="#sc_troubleshooting">Troubleshooting</a> +</li> +<li> +<a href="#sc_configuration">Configuration Parameters</a> +<ul class="minitoc"> +<li> +<a href="#sc_minimumConfiguration">Minimum Configuration</a> +</li> +<li> +<a href="#sc_advancedConfiguration">Advanced Configuration</a> +</li> +<li> +<a href="#sc_clusterOptions">Cluster Options</a> +</li> +<li> +<a href="#sc_authOptions">Authentication & Authorization Options</a> +</li> +<li> +<a href="#Experimental+Options%2FFeatures">Experimental Options/Features</a> +</li> +<li> +<a href="#Unsafe+Options">Unsafe Options</a> +</li> +<li> +<a href="#Communication+using+the+Netty+framework">Communication using the Netty framework</a> +</li> +</ul> +</li> +<li> +<a href="#sc_zkCommands">ZooKeeper Commands: The Four Letter Words</a> +</li> +<li> +<a href="#sc_dataFileManagement">Data File Management</a> +<ul class="minitoc"> +<li> +<a href="#The+Data+Directory">The Data Directory</a> +</li> +<li> +<a href="#The+Log+Directory">The Log Directory</a> +</li> +<li> +<a href="#sc_filemanagement">File Management</a> +</li> +</ul> +</li> +<li> +<a href="#sc_commonProblems">Things to Avoid</a> +</li> +<li> +<a href="#sc_bestPractices">Best Practices</a> +</li> +</ul> +</li> +</ul> +</div> +</div> + + + + + + + +<a name="ch_deployment"></a> +<h2 class="h3">Deployment</h2> +<div class="section"> +<p>This section contains information about deploying Zookeeper and + covers these topics:</p> +<ul> + +<li> + +<p> +<a href="#sc_systemReq">System Requirements</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_zkMulitServerSetup">Clustered (Multi-Server) Setup</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_singleAndDevSetup">Single Server and Developer Setup</a> +</p> + +</li> + +</ul> +<p>The first two sections assume you are interested in installing + ZooKeeper in a production environment such as a datacenter. The final + section covers situations in which you are setting up ZooKeeper on a + limited basis - for evaluation, testing, or development - but not in a + production environment.</p> +<a name="sc_systemReq"></a> +<h3 class="h4">System Requirements</h3> +<a name="sc_supportedPlatforms"></a> +<h4>Supported Platforms</h4> +<ul> + +<li> + +<p>GNU/Linux is supported as a development and production + platform for both server and client.</p> + +</li> + +<li> + +<p>Sun Solaris is supported as a development and production + platform for both server and client.</p> + +</li> + +<li> + +<p>FreeBSD is supported as a development and production + platform for clients only. Java NIO selector support in + the FreeBSD JVM is broken.</p> + +</li> + +<li> + +<p>Win32 is supported as a <em>development + platform</em> only for both server and client.</p> + +</li> + +<li> + +<p>MacOSX is supported as a <em>development + platform</em> only for both server and client.</p> + +</li> + +</ul> +<a name="sc_requiredSoftware"></a> +<h4>Required Software </h4> +<p>ZooKeeper runs in Java, release 1.6 or greater (JDK 6 or + greater). It runs as an <em>ensemble</em> of + ZooKeeper servers. Three ZooKeeper servers is the minimum + recommended size for an ensemble, and we also recommend that + they run on separate machines. At Yahoo!, ZooKeeper is + usually deployed on dedicated RHEL boxes, with dual-core + processors, 2GB of RAM, and 80GB IDE hard drives.</p> +<a name="sc_zkMulitServerSetup"></a> +<h3 class="h4">Clustered (Multi-Server) Setup</h3> +<p>For reliable ZooKeeper service, you should deploy ZooKeeper in a + cluster known as an <em>ensemble</em>. As long as a majority + of the ensemble are up, the service will be available. Because Zookeeper + requires a majority, it is best to use an + odd number of machines. For example, with four machines ZooKeeper can + only handle the failure of a single machine; if two machines fail, the + remaining two machines do not constitute a majority. However, with five + machines ZooKeeper can handle the failure of two machines. </p> + +<div class="note"> +<div class="label">Note</div> +<div class="content"> +<p>As mentioned in the Getting Started guide, a minimum of three servers are + required for a fault tolerant clustered setup, and it is strongly + recommended that you have an odd number of servers.</p> +<p>Usually three servers is more than enough for a production install, but + for maximum reliability during maintenance, you may wish to install + five servers. With three servers, if you perform maintenance on + one of them, you are vulnerable to a failure on one of the other + two servers during that maintenance. If you have five of them + running, you can take one down for maintenance, and know that + you're still OK if one of the other four suddenly fails.</p> +<p>Your redundancy considerations should include all aspects of your + environment. If you have three zookeeper servers, but their + network cables are all plugged into the same network switch, then + the failure of that switch will take down your entire ensemble.</p> +</div> +</div> + +<p>Here are the steps to setting a server that will be part of an + ensemble. These steps should be performed on every host in the + ensemble:</p> +<ol> + +<li> + +<p>Install the Java JDK. You can use the native packaging system + for your system, or download the JDK from:</p> + + +<p> +<a href="http://java.sun.com/javase/downloads/index.jsp";>http://java.sun.com/javase/downloads/index.jsp</a> +</p> + +</li> + + +<li> + +<p>Set the Java heap size. This is very important to avoid + swapping, which will seriously degrade ZooKeeper performance. To + determine the correct value, use load tests, and make sure you are + well below the usage limit that would cause you to swap. Be + conservative - use a maximum heap size of 3GB for a 4GB + machine.</p> + +</li> + + +<li> + +<p>Install the ZooKeeper Server Package. It can be downloaded + from: + </p> + +<p> + +<a href="http://zookeeper.apache.org/releases.html";> + http://zookeeper.apache.org/releases.html + </a> + +</p> + +</li> + + +<li> + +<p>Create a configuration file. This file can be called anything. + Use the following settings as a starting point:</p> + + +<pre class="code"> +tickTime=2000 +dataDir=/var/lib/zookeeper/ +clientPort=2181 +initLimit=5 +syncLimit=2 +server.1=zoo1:2888:3888 +server.2=zoo2:2888:3888 +server.3=zoo3:2888:3888</pre> + + +<p>You can find the meanings of these and other configuration + settings in the section <a href="#sc_configuration">Configuration Parameters</a>. A word + though about a few here:</p> + + +<p>Every machine that is part of the ZooKeeper ensemble should know + about every other machine in the ensemble. You accomplish this with + the series of lines of the form <strong>server.id=host:port:port</strong>. The parameters <strong>host</strong> and <strong>port</strong> are straightforward. You attribute the + server id to each machine by creating a file named + <span class="codefrag filename">myid</span>, one for each server, which resides in + that server's data directory, as specified by the configuration file + parameter <strong>dataDir</strong>.</p> +</li> + + +<li> +<p>The myid file + consists of a single line containing only the text of that machine's + id. So <span class="codefrag filename">myid</span> of server 1 would contain the text + "1" and nothing else. The id must be unique within the + ensemble and should have a value between 1 and 255.</p> + +</li> + + +<li> + +<p>If your configuration file is set up, you can start a + ZooKeeper server:</p> + + +<p> +<span class="codefrag computeroutput">$ java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf \ + org.apache.zookeeper.server.quorum.QuorumPeerMain zoo.cfg + </span> +</p> + + +<p>QuorumPeerMain starts a ZooKeeper server, + <a href="http://java.sun.com/javase/technologies/core/mntr-mgmt/javamanagement/";>JMX</a> + management beans are also registered which allows + management through a JMX management console. + The <a href="zookeeperJMX.html">ZooKeeper JMX + document</a> contains details on managing ZooKeeper with JMX. + </p> + + +<p>See the script <em>bin/zkServer.sh</em>, + which is included in the release, for an example + of starting server instances.</p> + + +</li> + + +<li> + +<p>Test your deployment by connecting to the hosts:</p> + + +<ul> + +<li> + +<p>In Java, you can run the following command to execute + simple operations:</p> + + +<p> +<span class="codefrag computeroutput">$ java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf:src/java/lib/jline-0.9.94.jar \ + org.apache.zookeeper.ZooKeeperMain -server 127.0.0.1:2181</span> +</p> + +</li> + + +<li> + +<p>In C, you can compile either the single threaded client or + the multithreaded client: or n the c subdirectory in the + ZooKeeper sources. This compiles the single threaded + client:</p> + + +<p> +<span class="codefrag computeroutput">$ make cli_st</span> +</p> + + +<p>And this compiles the mulithreaded client:</p> + + +<p> +<span class="codefrag computeroutput">$ make cli_mt</span> +</p> + +</li> + +</ul> + + +<p>Running either program gives you a shell in which to execute + simple file-system-like operations. To connect to ZooKeeper with the + multithreaded client, for example, you would run:</p> + + +<p> +<span class="codefrag computeroutput">$ cli_mt 127.0.0.1:2181</span> +</p> + +</li> + +</ol> +<a name="sc_singleAndDevSetup"></a> +<h3 class="h4">Single Server and Developer Setup</h3> +<p>If you want to setup ZooKeeper for development purposes, you will + probably want to setup a single server instance of ZooKeeper, and then + install either the Java or C client-side libraries and bindings on your + development machine.</p> +<p>The steps to setting up a single server instance are the similar + to the above, except the configuration file is simpler. You can find the + complete instructions in the <a href="zookeeperStarted.html#sc_InstallingSingleMode">Installing and + Running ZooKeeper in Single Server Mode</a> section of the <a href="zookeeperStarted.html">ZooKeeper Getting Started + Guide</a>.</p> +<p>For information on installing the client side libraries, refer to + the <a href="zookeeperProgrammers.html#Bindings">Bindings</a> + section of the <a href="zookeeperProgrammers.html">ZooKeeper + Programmer's Guide</a>.</p> +</div> + + +<a name="ch_administration"></a> +<h2 class="h3">Administration</h2> +<div class="section"> +<p>This section contains information about running and maintaining + ZooKeeper and covers these topics: </p> +<ul> + +<li> + +<p> +<a href="#sc_designing">Designing a ZooKeeper Deployment</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_provisioning">Provisioning</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_strengthsAndLimitations">Things to Consider: ZooKeeper Strengths and Limitations</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_administering">Administering</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_maintenance">Maintenance</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_supervision">Supervision</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_monitoring">Monitoring</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_logging">Logging</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_troubleshooting">Troubleshooting</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_configuration">Configuration Parameters</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_zkCommands">ZooKeeper Commands: The Four Letter Words</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_dataFileManagement">Data File Management</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_commonProblems">Things to Avoid</a> +</p> + +</li> + + +<li> + +<p> +<a href="#sc_bestPractices">Best Practices</a> +</p> + +</li> + +</ul> +<a name="sc_designing"></a> +<h3 class="h4">Designing a ZooKeeper Deployment</h3> +<p>The reliablity of ZooKeeper rests on two basic assumptions.</p> +<ol> + +<li> +<p> Only a minority of servers in a deployment + will fail. <em>Failure</em> in this context + means a machine crash, or some error in the network that + partitions a server off from the majority.</p> + +</li> + +<li> +<p> Deployed machines operate correctly. To + operate correctly means to execute code correctly, to have + clocks that work properly, and to have storage and network + components that perform consistently.</p> + +</li> + +</ol> +<p>The sections below contain considerations for ZooKeeper + administrators to maximize the probability for these assumptions + to hold true. Some of these are cross-machines considerations, + and others are things you should consider for each and every + machine in your deployment.</p> +<a name="sc_CrossMachineRequirements"></a> +<h4>Cross Machine Requirements</h4> +<p>For the ZooKeeper service to be active, there must be a + majority of non-failing machines that can communicate with + each other. To create a deployment that can tolerate the + failure of F machines, you should count on deploying 2xF+1 + machines. Thus, a deployment that consists of three machines + can handle one failure, and a deployment of five machines can + handle two failures. Note that a deployment of six machines + can only handle two failures since three machines is not a + majority. For this reason, ZooKeeper deployments are usually + made up of an odd number of machines.</p> +<p>To achieve the highest probability of tolerating a failure + you should try to make machine failures independent. For + example, if most of the machines share the same switch, + failure of that switch could cause a correlated failure and + bring down the service. The same holds true of shared power + circuits, cooling systems, etc.</p> +<a name="Single+Machine+Requirements"></a> +<h4>Single Machine Requirements</h4> +<p>If ZooKeeper has to contend with other applications for + access to resourses like storage media, CPU, network, or + memory, its performance will suffer markedly. ZooKeeper has + strong durability guarantees, which means it uses storage + media to log changes before the operation responsible for the + change is allowed to complete. You should be aware of this + dependency then, and take great care if you want to ensure + that ZooKeeper operations aren’t held up by your media. Here + are some things you can do to minimize that sort of + degradation: + </p> +<ul> + +<li> + +<p>ZooKeeper's transaction log must be on a dedicated + device. (A dedicated partition is not enough.) ZooKeeper + writes the log sequentially, without seeking Sharing your + log device with other processes can cause seeks and + contention, which in turn can cause multi-second + delays.</p> + +</li> + + +<li> + +<p>Do not put ZooKeeper in a situation that can cause a + swap. In order for ZooKeeper to function with any sort of + timeliness, it simply cannot be allowed to swap. + Therefore, make certain that the maximum heap size given + to ZooKeeper is not bigger than the amount of real memory + available to ZooKeeper. For more on this, see + <a href="#sc_commonProblems">Things to Avoid</a> + below. </p> + +</li> + +</ul> +<a name="sc_provisioning"></a> +<h3 class="h4">Provisioning</h3> +<p></p> +<a name="sc_strengthsAndLimitations"></a> +<h3 class="h4">Things to Consider: ZooKeeper Strengths and Limitations</h3> +<p></p> +<a name="sc_administering"></a> +<h3 class="h4">Administering</h3> +<p></p> +<a name="sc_maintenance"></a> +<h3 class="h4">Maintenance</h3> +<p>Little long term maintenance is required for a ZooKeeper + cluster however you must be aware of the following:</p> +<a name="Ongoing+Data+Directory+Cleanup"></a> +<h4>Ongoing Data Directory Cleanup</h4> +<p>The ZooKeeper <a href="#var_datadir">Data + Directory</a> contains files which are a persistent copy + of the znodes stored by a particular serving ensemble. These + are the snapshot and transactional log files. As changes are + made to the znodes these changes are appended to a + transaction log, occasionally, when a log grows large, a + snapshot of the current state of all znodes will be written + to the filesystem. This snapshot supercedes all previous + logs. + </p> +<p>A ZooKeeper server <strong>will not remove + old snapshots and log files</strong> when using the default + configuration (see autopurge below), this is the + responsibility of the operator. Every serving environment is + different and therefore the requirements of managing these + files may differ from install to install (backup for example). + </p> +<p>The PurgeTxnLog utility implements a simple retention + policy that administrators can use. The <a href="api/index.html">API docs</a> contains details on + calling conventions (arguments, etc...). + </p> +<p>In the following example the last count snapshots and + their corresponding logs are retained and the others are + deleted. The value of <count> should typically be + greater than 3 (although not required, this provides 3 backups + in the unlikely event a recent log has become corrupted). This + can be run as a cron job on the ZooKeeper server machines to + clean up the logs daily.</p> +<pre class="code"> java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf org.apache.zookeeper.server.PurgeTxnLog <dataDir> <snapDir> -n <count></pre> +<p>Automatic purging of the snapshots and corresponding + transaction logs was introduced in version 3.4.0 and can be + enabled via the following configuration parameters <strong>autopurge.snapRetainCount</strong> and <strong>autopurge.purgeInterval</strong>. For more on + this, see <a href="#sc_advancedConfiguration">Advanced Configuration</a> + below.</p> +<a name="Debug+Log+Cleanup+%28log4j%29"></a> +<h4>Debug Log Cleanup (log4j)</h4> +<p>See the section on <a href="#sc_logging">logging</a> in this document. It is + expected that you will setup a rolling file appender using the + in-built log4j feature. The sample configuration file in the + release tar's conf/log4j.properties provides an example of + this. + </p> +<a name="sc_supervision"></a> +<h3 class="h4">Supervision</h3> +<p>You will want to have a supervisory process that manages + each of your ZooKeeper server processes (JVM). The ZK server is + designed to be "fail fast" meaning that it will shutdown + (process exit) if an error occurs that it cannot recover + from. As a ZooKeeper serving cluster is highly reliable, this + means that while the server may go down the cluster as a whole + is still active and serving requests. Additionally, as the + cluster is "self healing" the failed server once restarted will + automatically rejoin the ensemble w/o any manual + interaction.</p> +<p>Having a supervisory process such as <a href="http://cr.yp.to/daemontools.html";>daemontools</a> or + <a href="http://en.wikipedia.org/wiki/Service_Management_Facility";>SMF</a> + (other options for supervisory process are also available, it's + up to you which one you would like to use, these are just two + examples) managing your ZooKeeper server ensures that if the + process does exit abnormally it will automatically be restarted + and will quickly rejoin the cluster.</p> +<a name="sc_monitoring"></a> +<h3 class="h4">Monitoring</h3> +<p>The ZooKeeper service can be monitored in one of two + primary ways; 1) the command port through the use of <a href="#sc_zkCommands">4 letter words</a> and 2) <a href="zookeeperJMX.html">JMX</a>. See the appropriate section for + your environment/requirements.</p> +<a name="sc_logging"></a> +<h3 class="h4">Logging</h3> +<p>ZooKeeper uses <strong>log4j</strong> version 1.2 as + its logging infrastructure. The ZooKeeper default <span class="codefrag filename">log4j.properties</span> + file resides in the <span class="codefrag filename">conf</span> directory. Log4j requires that + <span class="codefrag filename">log4j.properties</span> either be in the working directory + (the directory from which ZooKeeper is run) or be accessible from the classpath.</p> +<p>For more information, see + <a href="http://logging.apache.org/log4j/1.2/manual.html#defaultInit";>Log4j Default Initialization Procedure</a> + of the log4j manual.</p> +<a name="sc_troubleshooting"></a> +<h3 class="h4">Troubleshooting</h3> +<dl> + +<dt> +<term> Server not coming up because of file corruption</term> +</dt> +<dd> +<p>A server might not be able to read its database and fail to come up because of + some file corruption in the transaction logs of the ZooKeeper server. You will + see some IOException on loading ZooKeeper database. In such a case, + make sure all the other servers in your ensemble are up and working. Use "stat" + command on the command port to see if they are in good health. After you have verified that + all the other servers of the ensemble are up, you can go ahead and clean the database + of the corrupt server. Delete all the files in datadir/version-2 and datalogdir/version-2/. + Restart the server. + </p> +</dd> + +</dl> +<a name="sc_configuration"></a> +<h3 class="h4">Configuration Parameters</h3> +<p>ZooKeeper's behavior is governed by the ZooKeeper configuration + file. This file is designed so that the exact same file can be used by + all the servers that make up a ZooKeeper server assuming the disk + layouts are the same. If servers use different configuration files, care + must be taken to ensure that the list of servers in all of the different + configuration files match.</p> +<a name="sc_minimumConfiguration"></a> +<h4>Minimum Configuration</h4> +<p>Here are the minimum configuration keywords that must be defined + in the configuration file:</p> +<dl> + +<dt> +<term>clientPort</term> +</dt> +<dd> +<p>the port to listen for client connections; that is, the + port that clients attempt to connect to.</p> +</dd> + + +<dt> +<term>dataDir</term> +</dt> +<dd> +<p>the location where ZooKeeper will store the in-memory + database snapshots and, unless specified otherwise, the + transaction log of updates to the database.</p> +<div class="note"> +<div class="label">Note</div> +<div class="content"> + +<p>Be careful where you put the transaction log. A + dedicated transaction log device is key to consistent good + performance. Putting the log on a busy device will adversely + effect performance.</p> + +</div> +</div> +</dd> + + +<dt> +<term>tickTime</term> +</dt> +<dd> +<p>the length of a single tick, which is the basic time unit + used by ZooKeeper, as measured in milliseconds. It is used to + regulate heartbeats, and timeouts. For example, the minimum + session timeout will be two ticks.</p> +</dd> + +</dl> +<a name="sc_advancedConfiguration"></a> +<h4>Advanced Configuration</h4> +<p>The configuration settings in the section are optional. You can + use them to further fine tune the behaviour of your ZooKeeper servers. + Some can also be set using Java system properties, generally of the + form <em>zookeeper.keyword</em>. The exact system + property, when available, is noted below.</p> +<dl> + +<dt> +<term>dataLogDir</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p>This option will direct the machine to write the + transaction log to the <strong>dataLogDir</strong> rather than the <strong>dataDir</strong>. This allows a dedicated log + device to be used, and helps avoid competition between logging + and snaphots.</p> +<div class="note"> +<div class="label">Note</div> +<div class="content"> + +<p>Having a dedicated log device has a large impact on + throughput and stable latencies. It is highly recommened to + dedicate a log device and set <strong>dataLogDir</strong> to point to a directory on + that device, and then make sure to point <strong>dataDir</strong> to a directory + <em>not</em> residing on that device.</p> + +</div> +</div> +</dd> + + +<dt> +<term>globalOutstandingLimit</term> +</dt> +<dd> +<p>(Java system property: <strong>zookeeper.globalOutstandingLimit.</strong>)</p> +<p>Clients can submit requests faster than ZooKeeper can + process them, especially if there are a lot of clients. To + prevent ZooKeeper from running out of memory due to queued + requests, ZooKeeper will throttle clients so that there is no + more than globalOutstandingLimit outstanding requests in the + system. The default limit is 1,000.</p> +</dd> + + +<dt> +<term>preAllocSize</term> +</dt> +<dd> +<p>(Java system property: <strong>zookeeper.preAllocSize</strong>)</p> +<p>To avoid seeks ZooKeeper allocates space in the + transaction log file in blocks of preAllocSize kilobytes. The + default block size is 64M. One reason for changing the size of + the blocks is to reduce the block size if snapshots are taken + more often. (Also, see <strong>snapCount</strong>).</p> +</dd> + + +<dt> +<term>snapCount</term> +</dt> +<dd> +<p>(Java system property: <strong>zookeeper.snapCount</strong>)</p> +<p>ZooKeeper logs transactions to a transaction + log. After snapCount transactions are written to a log + file a snapshot is started and a new transaction log + file is created. The default snapCount is + 100,000.</p> +</dd> + + +<dt> +<term>traceFile</term> +</dt> +<dd> +<p>(Java system property: <strong>requestTraceFile</strong>)</p> +<p>If this option is defined, requests will be will logged to + a trace file named traceFile.year.month.day. Use of this option + provides useful debugging information, but will impact + performance. (Note: The system property has no zookeeper prefix, + and the configuration variable name is different from the system + property. Yes - it's not consistent, and it's annoying.)</p> +</dd> + + +<dt> +<term>maxClientCnxns</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p>Limits the number of concurrent connections (at the socket + level) that a single client, identified by IP address, may make + to a single member of the ZooKeeper ensemble. This is used to + prevent certain classes of DoS attacks, including file + descriptor exhaustion. The default is 60. Setting this to 0 + entirely removes the limit on concurrent connections.</p> +</dd> + + +<dt> +<term>clientPortAddress</term> +</dt> +<dd> +<p> +<strong>New in 3.3.0:</strong> the + address (ipv4, ipv6 or hostname) to listen for client + connections; that is, the address that clients attempt + to connect to. This is optional, by default we bind in + such a way that any connection to the <strong>clientPort</strong> for any + address/interface/nic on the server will be + accepted.</p> +</dd> + + +<dt> +<term>minSessionTimeout</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p> +<strong>New in 3.3.0:</strong> the + minimum session timeout in milliseconds that the server + will allow the client to negotiate. Defaults to 2 times + the <strong>tickTime</strong>.</p> +</dd> + + +<dt> +<term>maxSessionTimeout</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p> +<strong>New in 3.3.0:</strong> the + maximum session timeout in milliseconds that the server + will allow the client to negotiate. Defaults to 20 times + the <strong>tickTime</strong>.</p> +</dd> + + +<dt> +<term>fsync.warningthresholdms</term> +</dt> +<dd> +<p>(Java system property: <strong>fsync.warningthresholdms</strong>)</p> +<p> +<strong>New in 3.3.4:</strong> A + warning message will be output to the log whenever an + fsync in the Transactional Log (WAL) takes longer than + this value. The values is specified in milliseconds and + defaults to 1000. This value can only be set as a + system property.</p> +</dd> + + +<dt> +<term>autopurge.snapRetainCount</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p> +<strong>New in 3.4.0:</strong> + When enabled, ZooKeeper auto purge feature retains + the <strong>autopurge.snapRetainCount</strong> most + recent snapshots and the corresponding transaction logs in the + <strong>dataDir</strong> and <strong>dataLogDir</strong> respectively and deletes the rest. + Defaults to 3. Minimum value is 3.</p> +</dd> + + +<dt> +<term>autopurge.purgeInterval</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p> +<strong>New in 3.4.0:</strong> The + time interval in hours for which the purge task has to + be triggered. Set to a positive integer (1 and above) + to enable the auto purging. Defaults to 0.</p> +</dd> + + +<dt> +<term>syncEnabled</term> +</dt> +<dd> +<p>(Java system property: <strong>zookeeper.observer.syncEnabled</strong>)</p> +<p> +<strong>New in 3.4.6, 3.5.0:</strong> + The observers now log transaction and write snapshot to disk + by default like the participants. This reduces the recovery time + of the observers on restart. Set to "false" to disable this + feature. Default is "true"</p> +</dd> + +</dl> +<a name="sc_clusterOptions"></a> +<h4>Cluster Options</h4> +<p>The options in this section are designed for use with an ensemble + of servers -- that is, when deploying clusters of servers.</p> +<dl> + +<dt> +<term>electionAlg</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p>Election implementation to use. A value of "0" corresponds + to the original UDP-based version, "1" corresponds to the + non-authenticated UDP-based version of fast leader election, "2" + corresponds to the authenticated UDP-based version of fast + leader election, and "3" corresponds to TCP-based version of + fast leader election. Currently, algorithm 3 is the default</p> +<div class="note"> +<div class="label">Note</div> +<div class="content"> + +<p> The implementations of leader election 0, 1, and 2 are now + <strong> deprecated </strong>. We have the intention + of removing them in the next release, at which point only the + FastLeaderElection will be available. + </p> + +</div> +</div> +</dd> + + +<dt> +<term>initLimit</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p>Amount of time, in ticks (see <a href="#id_tickTime">tickTime</a>), to allow followers to + connect and sync to a leader. Increased this value as needed, if + the amount of data managed by ZooKeeper is large.</p> +</dd> + + +<dt> +<term>leaderServes</term> +</dt> +<dd> +<p>(Java system property: zookeeper.<strong>leaderServes</strong>)</p> +<p>Leader accepts client connections. Default value is "yes". + The leader machine coordinates updates. For higher update + throughput at thes slight expense of read throughput the leader + can be configured to not accept clients and focus on + coordination. The default to this option is yes, which means + that a leader will accept client connections.</p> +<div class="note"> +<div class="label">Note</div> +<div class="content"> + +<p>Turning on leader selection is highly recommended when + you have more than three ZooKeeper servers in an ensemble.</p> + +</div> +</div> +</dd> + + +<dt> +<term>server.x=[hostname]:nnnnn[:nnnnn], etc</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p>servers making up the ZooKeeper ensemble. When the server + starts up, it determines which server it is by looking for the + file <span class="codefrag filename">myid</span> in the data directory. That file + contains the server number, in ASCII, and it should match + <strong>x</strong> in <strong>server.x</strong> in the left hand side of this + setting.</p> +<p>The list of servers that make up ZooKeeper servers that is + used by the clients must match the list of ZooKeeper servers + that each ZooKeeper server has.</p> +<p>There are two port numbers <strong>nnnnn</strong>. + The first followers use to connect to the leader, and the second is for + leader election. The leader election port is only necessary if electionAlg + is 1, 2, or 3 (default). If electionAlg is 0, then the second port is not + necessary. If you want to test multiple servers on a single machine, then + different ports can be used for each server.</p> +</dd> + + +<dt> +<term>syncLimit</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p>Amount of time, in ticks (see <a href="#id_tickTime">tickTime</a>), to allow followers to sync + with ZooKeeper. If followers fall too far behind a leader, they + will be dropped.</p> +</dd> + + +<dt> +<term>group.x=nnnnn[:nnnnn]</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p>Enables a hierarchical quorum construction."x" is a group identifier + and the numbers following the "=" sign correspond to server identifiers. + The left-hand side of the assignment is a colon-separated list of server + identifiers. Note that groups must be disjoint and the union of all groups + must be the ZooKeeper ensemble. </p> +<p> You will find an example <a href="zookeeperHierarchicalQuorums.html">here</a> + +</p> +</dd> + + +<dt> +<term>weight.x=nnnnn</term> +</dt> +<dd> +<p>(No Java system property)</p> +<p>Used along with "group", it assigns a weight to a server when + forming quorums. Such a value corresponds to the weight of a server + when voting. There are a few parts of ZooKeeper that require voting + such as leader election and the atomic broadcast protocol. By default + the weight of server is 1. If the configuration defines groups, but not + weights, then a value of 1 will be assigned to all servers. + </p> +<p> You will find an example <a href="zookeeperHierarchicalQuorums.html">here</a> + +</p> +</dd> + + +<dt> +<term>cnxTimeout</term> +</dt> +<dd> +<p>(Java system property: zookeeper.<strong>cnxTimeout</strong>)</p> +<p>Sets the timeout value for opening connections for leader election notifications. + Only applicable if you are using electionAlg 3. + </p> +<div class="note"> +<div class="label">Note</div> +<div class="content"> + +<p>Default value is 5 seconds.</p> + +</div> +</div> +</dd> + +</dl> +<p></p> +<a name="sc_authOptions"></a> +<h4>Authentication & Authorization Options</h4> +<p>The options in this section allow control over + authentication/authorization performed by the service.</p> +<dl> + +<dt> +<term>zookeeper.DigestAuthenticationProvider.superDigest</term> +</dt> +<dd> +<p>(Java system property only: <strong>zookeeper.DigestAuthenticationProvider.superDigest</strong>)</p> +<p>By default this feature is <strong>disabled</strong> +</p> +<p> +<strong>New in 3.2:</strong> + Enables a ZooKeeper ensemble administrator to access the + znode hierarchy as a "super" user. In particular no ACL + checking occurs for a user authenticated as + super.</p> +<p>org.apache.zookeeper.server.auth.DigestAuthenticationProvider + can be used to generate the superDigest, call it with + one parameter of "super:<password>". Provide the + generated "super:<data>" as the system property value + when starting each server of the ensemble.</p> +<p>When authenticating to a ZooKeeper server (from a + ZooKeeper client) pass a scheme of "digest" and authdata + of "super:<password>". Note that digest auth passes + the authdata in plaintext to the server, it would be + prudent to use this authentication method only on + localhost (not over the network) or over an encrypted + connection.</p> +</dd> + +</dl> +<a name="Experimental+Options%2FFeatures"></a> +<h4>Experimental Options/Features</h4> +<p>New features that are currently considered experimental.</p> +<dl> + +<dt> +<term>Read Only Mode Server</term> +</dt> +<dd> +<p>(Java system property: <strong>readonlymode.enabled</strong>)</p> +<p> +<strong>New in 3.4.0:</strong> + Setting this value to true enables Read Only Mode server + support (disabled by default). ROM allows clients + sessions which requested ROM support to connect to the + server even when the server might be partitioned from + the quorum. In this mode ROM clients can still read + values from the ZK service, but will be unable to write + values and see changes from other clients. See + ZOOKEEPER-784 for more details. + </p> +</dd> + + +</dl> +<a name="Unsafe+Options"></a> +<h4>Unsafe Options</h4> +<p>The following options can be useful, but be careful when you use + them. The risk of each is explained along with the explanation of what + the variable does.</p> +<dl> + +<dt> +<term>forceSync</term> +</dt> +<dd> +<p>(Java system property: <strong>zookeeper.forceSync</strong>)</p> +<p>Requires updates to be synced to media of the transaction + log before finishing processing the update. If this option is + set to no, ZooKeeper will not require updates to be synced to + the media.</p> +</dd> + + +<dt> +<term>jute.maxbuffer:</term> +</dt> +<dd> +<p>(Java system property:<strong> + jute.maxbuffer</strong>)</p> +<p>This option can only be set as a Java system property. + There is no zookeeper prefix on it. It specifies the maximum + size of the data that can be stored in a znode. The default is + 0xfffff, or just under 1M. If this option is changed, the system + property must be set on all servers and clients otherwise + problems will arise. This is really a sanity check. ZooKeeper is + designed to store data on the order of kilobytes in size.</p> +</dd> + + +<dt> +<term>skipACL</term> +</dt> +<dd> +<p>(Java system property: <strong>zookeeper.skipACL</strong>)</p> +<p>Skips ACL checks. This results in a boost in throughput, + but opens up full access to the data tree to everyone.</p> +</dd> + + +<dt> +<term>quorumListenOnAllIPs</term> +</dt> +<dd> +<p>When set to true the ZooKeeper server will listen + for connections from its peers on all available IP addresses, + and not only the address configured in the server list of the + configuration file. It affects the connections handling the + ZAB protocol and the Fast Leader Election protocol. Default + value is <strong>false</strong>.</p> +</dd> + + +</dl> +<a name="Communication+using+the+Netty+framework"></a> +<h4>Communication using the Netty framework</h4> +<p> +<strong>New in + 3.4:</strong> <a href="http://jboss.org/netty";>Netty</a> + is an NIO based client/server communication framework, it + simplifies (over NIO being used directly) many of the + complexities of network level communication for java + applications. Additionally the Netty framework has built + in support for encryption (SSL) and authentication + (certificates). These are optional features and can be + turned on or off individually. + </p> +<p>Prior to version 3.4 ZooKeeper has always used NIO + directly, however in versions 3.4 and later Netty is + supported as an option to NIO (replaces). NIO continues to + be the default, however Netty based communication can be + used in place of NIO by setting the environment variable + "zookeeper.serverCnxnFactory" to + "org.apache.zookeeper.server.NettyServerCnxnFactory". You + have the option of setting this on either the client(s) or + server(s), typically you would want to set this on both, + however that is at your discretion. + </p> +<p> + TBD - tuning options for netty - currently there are none that are netty specific but we should add some. Esp around max bound on the number of reader worker threads netty creates. + </p> +<p> + TBD - how to manage encryption + </p> +<p> + TBD - how to manage certificates + </p> +<a name="sc_zkCommands"></a> +<h3 class="h4">ZooKeeper Commands: The Four Letter Words</h3> +<p>ZooKeeper responds to a small set of commands. Each command is + composed of four letters. You issue the commands to ZooKeeper via telnet + or nc, at the client port.</p> +<p>Three of the more interesting commands: "stat" gives some + general information about the server and connected clients, + while "srvr" and "cons" give extended details on server and + connections respectively.</p> +<dl> + +<dt> +<term>conf</term> +</dt> +<dd> +<p> +<strong>New in 3.3.0:</strong> Print + details about serving configuration.</p> +</dd> + + +<dt> +<term>cons</term> +</dt> +<dd> +<p> +<strong>New in 3.3.0:</strong> List + full connection/session details for all clients connected + to this server. Includes information on numbers of packets + received/sent, session id, operation latencies, last + operation performed, etc...</p> +</dd> + + +<dt> +<term>crst</term> +</dt> +<dd> +<p> +<strong>New in 3.3.0:</strong> Reset + connection/session statistics for all connections.</p> +</dd> + + +<dt> +<term>dump</term> +</dt> +<dd> +<p>Lists the outstanding sessions and ephemeral nodes. This + only works on the leader.</p> +</dd> + + +<dt> +<term>envi</term> +</dt> +<dd> +<p>Print details about serving environment</p> +</dd> + + +<dt> +<term>ruok</term> +</dt> +<dd> +<p>Tests if server is running in a non-error state. The server + will respond with imok if it is running. Otherwise it will not + respond at all.</p> +<p>A response of "imok" does not necessarily indicate that the + server has joined the quorum, just that the server process is active + and bound to the specified client port. Use "stat" for details on + state wrt quorum and client connection information.</p> +</dd> + + +<dt> +<term>srst</term> +</dt> +<dd> +<p>Reset server statistics.</p> +</dd> + + +<dt> +<term>srvr</term> +</dt> +<dd> +<p> +<strong>New in 3.3.0:</strong> Lists + full details for the server.</p> +</dd> + + +<dt> +<term>stat</term> +</dt> +<dd> +<p>Lists brief details for the server and connected + clients.</p> +</dd> + + +<dt> +<term>wchs</term> +</dt> +<dd> +<p> +<strong>New in 3.3.0:</strong> Lists + brief information on watches for the server.</p> +</dd> + + +<dt> +<term>wchc</term> +</dt> +<dd> +<p> +<strong>New in 3.3.0:</strong> Lists + detailed information on watches for the server, by + session. This outputs a list of sessions(connections) + with associated watches (paths). Note, depending on the + number of watches this operation may be expensive (ie + impact server performance), use it carefully.</p> +</dd> + + +<dt> +<term>wchp</term> +</dt> +<dd> +<p> +<strong>New in 3.3.0:</strong> Lists + detailed information on watches for the server, by path. + This outputs a list of paths (znodes) with associated + sessions. Note, depending on the number of watches this + operation may be expensive (ie impact server performance), + use it carefully.</p> +</dd> + + + +<dt> +<term>mntr</term> +</dt> +<dd> +<p> +<strong>New in 3.4.0:</strong> Outputs a list + of variables that could be used for monitoring the health of the cluster.</p> +<pre class="code">$ echo mntr | nc localhost 2185 + +zk_version 3.4.0 +zk_avg_latency 0 +zk_max_latency 0 +zk_min_latency 0 +zk_packets_received 70 +zk_packets_sent 69 +zk_outstanding_requests 0 +zk_server_state leader +zk_znode_count 4 +zk_watch_count 0 +zk_ephemerals_count 0 +zk_approximate_data_size 27 +zk_followers 4 - only exposed by the Leader +zk_synced_followers 4 - only exposed by the Leader +zk_pending_syncs 0 - only exposed by the Leader +zk_open_file_descriptor_count 23 - only available on Unix platforms +zk_max_file_descriptor_count 1024 - only available on Unix platforms +</pre> +<p>The output is compatible with java properties format and the content + may change over time (new keys added). Your scripts should expect changes.</p> +<p>ATTENTION: Some of the keys are platform specific and some of the keys are only exported by the Leader. </p> +<p>The output contains multiple lines with the following format:</p> +<pre class="code">key \t value</pre> +</dd> + +</dl> +<p>Here's an example of the <strong>ruok</strong> + command:</p> +<pre class="code">$ echo ruok | nc 127.0.0.1 5111 +imok +</pre> +<a name="sc_dataFileManagement"></a> +<h3 class="h4">Data File Management</h3> +<p>ZooKeeper stores its data in a data directory and its transaction + log in a transaction log directory. By default these two directories are + the same. The server can (and should) be configured to store the + transaction log files in a separate directory than the data files. + Throughput increases and latency decreases when transaction logs reside + on a dedicated log devices.</p> +<a name="The+Data+Directory"></a> +<h4>The Data Directory</h4> +<p>This directory has two files in it:</p> +<ul> + +<li> + +<p> +<span class="codefrag filename">myid</span> - contains a single integer in + human readable ASCII text that represents the server id.</p> + +</li> + + +<li> + +<p> +<span class="codefrag filename">snapshot.<zxid></span> - holds the fuzzy + snapshot of a data tree.</p> + +</li> + +</ul> +<p>Each ZooKeeper server has a unique id. This id is used in two + places: the <span class="codefrag filename">myid</span> file and the configuration file. + The <span class="codefrag filename">myid</span> file identifies the server that + corresponds to the given data directory. The configuration file lists + the contact information for each server identified by its server id. + When a ZooKeeper server instance starts, it reads its id from the + <span class="codefrag filename">myid</span> file and then, using that id, reads from the + configuration file, looking up the port on which it should + listen.</p> +<p>The <span class="codefrag filename">snapshot</span> files stored in the data + directory are fuzzy snapshots in the sense that during the time the + ZooKeeper server is taking the snapshot, updates are occurring to the + data tree. The suffix of the <span class="codefrag filename">snapshot</span> file names + is the <em>zxid</em>, the ZooKeeper transaction id, of the + last committed transaction at the start of the snapshot. Thus, the + snapshot includes a subset of the updates to the data tree that + occurred while the snapshot was in process. The snapshot, then, may + not correspond to any data tree that actually existed, and for this + reason we refer to it as a fuzzy snapshot. Still, ZooKeeper can + recover using this snapshot because it takes advantage of the + idempotent nature of its updates. By replaying the transaction log + against fuzzy snapshots ZooKeeper gets the state of the system at the + end of the log.</p> +<a name="The+Log+Directory"></a> +<h4>The Log Directory</h4> +<p>The Log Directory contains the ZooKeeper transaction logs. + Before any update takes place, ZooKeeper ensures that the transaction + that represents the update is written to non-volatile storage. A new + log file is started each time a snapshot is begun. The log file's + suffix is the first zxid written to that log.</p> +<a name="sc_filemanagement"></a> +<h4>File Management</h4> +<p>The format of snapshot and log files does not change between + standalone ZooKeeper servers and different configurations of + replicated ZooKeeper servers. Therefore, you can pull these files from + a running replicated ZooKeeper server to a development machine with a + stand-alone ZooKeeper server for trouble shooting.</p> +<p>Using older log and snapshot files, you can look at the previous + state of ZooKeeper servers and even restore that state. The + LogFormatter class allows an administrator to look at the transactions + in a log.</p> +<p>The ZooKeeper server creates snapshot and log files, but + never deletes them. The retention policy of the data and log + files is implemented outside of the ZooKeeper server. The + server itself only needs the latest complete fuzzy snapshot + and the log files from the start of that snapshot. See the + <a href="#sc_maintenance">maintenance</a> section in + this document for more details on setting a retention policy + and maintenance of ZooKeeper storage. + </p> +<a name="sc_commonProblems"></a> +<h3 class="h4">Things to Avoid</h3> +<p>Here are some common problems you can avoid by configuring + ZooKeeper correctly:</p> +<dl> + +<dt> +<term>inconsistent lists of servers</term> +</dt> +<dd> +<p>The list of ZooKeeper servers used by the clients must match + the list of ZooKeeper servers that each ZooKeeper server has. + Things work okay if the client list is a subset of the real list, + but things will really act strange if clients have a list of + ZooKeeper servers that are in different ZooKeeper clusters. Also, + the server lists in each Zookeeper server configuration file + should be consistent with one another.</p> +</dd> + + +<dt> +<term>incorrect placement of transasction log</term> +</dt> +<dd> +<p>The most performance critical part of ZooKeeper is the + transaction log. ZooKeeper syncs transactions to media before it + returns a response. A dedicated transaction log device is key to + consistent good performance. Putting the log on a busy device will + adversely effect performance. If you only have one storage device, + put trace files on NFS and increase the snapshotCount; it doesn't + eliminate the problem, but it should mitigate it.</p> +</dd> + + +<dt> +<term>incorrect Java heap size</term> +</dt> +<dd> +<p>You should take special care to set your Java max heap size + correctly. In particular, you should not create a situation in + which ZooKeeper swaps to disk. The disk is death to ZooKeeper. + Everything is ordered, so if processing one request swaps the + disk, all other queued requests will probably do the same. the + disk. DON'T SWAP.</p> +<p>Be conservative in your estimates: if you have 4G of RAM, do + not set the Java max heap size to 6G or even 4G. For example, it + is more likely you would use a 3G heap for a 4G machine, as the + operating system and the cache also need memory. The best and only + recommend practice for estimating the heap size your system needs + is to run load tests, and then make sure you are well below the + usage limit that would cause the system to swap.</p> +</dd> + +</dl> +<a name="sc_bestPractices"></a> +<h3 class="h4">Best Practices</h3> +<p>For best results, take note of the following list of good + Zookeeper practices:</p> +<p>For multi-tennant installations see the <a href="zookeeperProgrammers.html#ch_zkSessions">section</a> + detailing ZooKeeper "chroot" support, this can be very useful + when deploying many applications/services interfacing to a + single ZooKeeper cluster.</p> +</div> + +<p align="right"> +<font size="-2"></font> +</p> +</div> +<!--+ + |end content + +--> +<div class="clearboth"> </div> +</div> +<div id="footer"> +<!--+ + |start bottomstrip + +--> +<div class="lastmodified"> +<script type="text/javascript"><!-- +document.write("Last Published: " + document.lastModified); +// --></script> +</div> +<div class="copyright"> + Copyright © + 2008-2013 <a href="http://www.apache.org/licenses/";>The Apache Software Foundation.</a> +</div> +<!--+ + |end bottomstrip + +--> +</div> +</body> +</html> Added: websites/staging/zookeeper/trunk/content/doc/r3.4.7/zookeeperAdmin.pdf ============================================================================== Binary file - no diff available. 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The basic idea is + very simple. First, we split servers into groups, and add a line for each group listing + the servers that form this group. Next we have to assign a weight to each server. + </p> + + +<p> + The following example shows how to configure a system with three groups of three servers + each, and we assign a weight of 1 to each server: + </p> + + +<pre class="code"> + group.1=1:2:3 + group.2=4:5:6 + group.3=7:8:9 + + weight.1=1 + weight.2=1 + weight.3=1 + weight.4=1 + weight.5=1 + weight.6=1 + weight.7=1 + weight.8=1 + weight.9=1 + </pre> + + +<p> + When running the system, we are able to form a quorum once we have a majority of votes from + a majority of non-zero-weight groups. Groups that have zero weight are discarded and not + considered when forming quorums. Looking at the example, we are able to form a quorum once + we have votes from at least two servers from each of two different groups. + </p> + +<p align="right"> +<font size="-2"></font> +</p> +</div> +<!--+ + |end content + +--> +<div class="clearboth"> </div> +</div> +<div id="footer"> +<!--+ + |start bottomstrip + +--> +<div class="lastmodified"> +<script type="text/javascript"><!-- +document.write("Last Published: " + document.lastModified); +// --></script> +</div> +<div class="copyright"> + Copyright © + 2008-2013 <a href="http://www.apache.org/licenses/";>The Apache Software Foundation.</a> +</div> +<!--+ + |end bottomstrip + +--> +</div> +</body> +</html> Added: websites/staging/zookeeper/trunk/content/doc/r3.4.7/zookeeperHierarchicalQuorums.pdf ============================================================================== Binary file - no diff available. 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