http://git-wip-us.apache.org/repos/asf/zookeeper/blob/ab59048a/docs/zookeeperAdmin.html ---------------------------------------------------------------------- diff --git a/docs/zookeeperAdmin.html b/docs/zookeeperAdmin.html deleted file mode 100644 index 487c853..0000000 --- a/docs/zookeeperAdmin.html +++ /dev/null @@ -1,2669 +0,0 @@ -<!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 3.5 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_selected_1.3', 'skin/')" id="menu_selected_1.3Title" class="menutitle" style="background-image: url('skin/images/chapter_open.gif');">Admin & Ops</div> -<div id="menu_selected_1.3" 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 class="menuitem"> -<a href="zookeeperReconfig.html">Dynamic Reconfiguration</a> -</div> -</div> -<div onclick="SwitchMenu('menu_1.4', 'skin/')" id="menu_1.4Title" class="menutitle">Contributor</div> -<div id="menu_1.4" class="menuitemgroup"> -<div class="menuitem"> -<a href="zookeeperInternals.html">ZooKeeper Internals</a> -</div> -</div> -<div onclick="SwitchMenu('menu_1.5', 'skin/')" id="menu_1.5Title" class="menutitle">Miscellaneous</div> -<div id="menu_1.5" 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">Encryption, 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="#Disabling+data+directory+autocreation">Disabling data directory autocreation</a> -</li> -<li> -<a href="#sc_performance_options">Performance Tuning Options</a> -</li> -<li> -<a href="#Communication+using+the+Netty+framework">Communication using the Netty framework</a> -</li> -<li> -<a href="#sc_adminserver_config">AdminServer configuration</a> -</li> -</ul> -</li> -<li> -<a href="#sc_zkCommands">ZooKeeper Commands</a> -<ul class="minitoc"> -<li> -<a href="#sc_4lw">The Four Letter Words</a> -</li> -<li> -<a href="#sc_adminserver">The AdminServer</a> -</li> -</ul> -</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> -<li> -<a href="#Recovery+-+TxnLogToolkit">Recovery - TxnLogToolkit</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> -<p>ZooKeeper consists of multiple components. Some components are - supported broadly, and other components are supported only on a smaller - set of platforms.</p> -<ul> - -<li> - -<p> -<strong>Client</strong> is the Java client - library, used by applications to connect to a ZooKeeper ensemble. - </p> - -</li> - -<li> - -<p> -<strong>Server</strong> is the Java server - that runs on the ZooKeeper ensemble nodes.</p> - -</li> - -<li> - -<p> -<strong>Native Client</strong> is a client - implemented in C, similar to the Java client, used by applications - to connect to a ZooKeeper ensemble.</p> - -</li> - -<li> - -<p> -<strong>Contrib</strong> refers to multiple - optional add-on components.</p> - -</li> - -</ul> -<p>The following matrix describes the level of support committed for - running each component on different operating system platforms.</p> -<table class="ForrestTable" cellspacing="1" cellpadding="4"> -<caption>Support Matrix</caption> - -<title>Support Matrix</title> - - -<tr> - -<th>Operating System</th> - <th>Client</th> - <th>Server</th> - <th>Native Client</th> - <th>Contrib</th> - -</tr> - - -<tr> - -<td>GNU/Linux</td> - <td>Development and Production</td> - <td>Development and Production</td> - <td>Development and Production</td> - <td>Development and Production</td> - -</tr> - -<tr> - -<td>Solaris</td> - <td>Development and Production</td> - <td>Development and Production</td> - <td>Not Supported</td> - <td>Not Supported</td> - -</tr> - -<tr> - -<td>FreeBSD</td> - <td>Development and Production</td> - <td>Development and Production</td> - <td>Not Supported</td> - <td>Not Supported</td> - -</tr> - -<tr> - -<td>Windows</td> - <td>Development and Production</td> - <td>Development and Production</td> - <td>Not Supported</td> - <td>Not Supported</td> - -</tr> - -<tr> - -<td>Mac OS X</td> - <td>Development Only</td> - <td>Development Only</td> - <td>Not Supported</td> - <td>Not Supported</td> - -</tr> - - -</table> -<p>For any operating system not explicitly mentioned as supported in - the matrix, components may or may not work. The ZooKeeper community - will fix obvious bugs that are reported for other platforms, but there - is no full support.</p> -<a name="sc_requiredSoftware"></a> -<h4>Required Software </h4> -<p>ZooKeeper runs in Java, release 1.8 or greater (JDK 8 or - greater, FreeBSD support requires openjdk8). 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 - <a href="zookeeperStarted.html">ZooKeeper Getting Started Guide</a> - , 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. <strong>IMPORTANT:</strong> if you - enable extended features such as TTL Nodes (see below) the id must be - between 1 and 254 due to internal limitations.</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-1.7.5.jar:lib/slf4j-log4j12-1.7.5.jar:lib/log4j-1.2.17.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> - - -<p>In Java, you can run the following command to execute - simple operations:</p> - - -<p> -<span class="codefrag computeroutput">$ bin/zkCli.sh -server 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</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 resources 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 and a new transaction log file is created - for future transactions. During snapshotting, ZooKeeper may - continue appending incoming transactions to the old log file. - Therefore, some transactions which are newer than a snapshot - may be found in the last transaction log preceding the - snapshot. - </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-1.7.5.jar:lib/slf4j-log4j12-1.7.5.jar:lib/log4j-1.2.17.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> -<p>It is also recommended to configure the ZooKeeper server process to - terminate and dump its heap if an - <span class="codefrag computeroutput">OutOfMemoryError</span> occurs. This is achieved - by launching the JVM with the following arguments on Linux and Windows - respectively. The <span class="codefrag filename">zkServer.sh</span> and - <span class="codefrag filename">zkServer.cmd</span> scripts that ship with ZooKeeper set - these options. - </p> -<pre class="code">-XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p'</pre> -<pre class="code">"-XX:+HeapDumpOnOutOfMemoryError" "-XX:OnOutOfMemoryError=cmd /c taskkill /pid %%%%p /t /f"</pre> -<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><a href="http://www.slf4j.org";>SLF4J</a></strong> - version 1.7.5 as its logging infrastructure. For backward compatibility it is bound to - <strong>LOG4J</strong> but you can use - <strong><a href="http://logback.qos.ch/";>LOGBack</a></strong> - or any other supported logging framework of your choice. - </p> -<p> - 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 about SLF4J, see - <a href="http://www.slf4j.org/manual.html";>its manual</a>.</p> -<p>For more information about LOG4J, 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> -<div class="note"> -<div class="label">Note</div> -<div class="content"> - -<p>In 3.5.0 and later, some of these parameters should be placed in - a dynamic configuration file. If they are placed in the static - configuration file, ZooKeeper will automatically move them over to the - dynamic configuration file. See <a href="zookeeperReconfig.html"> - Dynamic Reconfiguration</a> for more information.</p> - -</div> -</div> -<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>secureClientPort</term> -</dt> -<dd> -<p>the port to listen on for secure client connections using SSL. - - <strong>clientPort</strong> specifies - the port for plaintext connections while <strong> - secureClientPort</strong> specifies the port for SSL - connections. Specifying both enables mixed-mode while omitting - either will disable that mode.</p> -<p>Note that SSL feature will be enabled when user plugs-in - zookeeper.serverCnxnFactory, zookeeper.clientCnxnSocket as Netty.</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 records its transactions using snapshots and - a transaction log (think write-ahead log).The number of - transactions recorded in the transaction log before a snapshot - can be taken (and the transaction log rolled) is determined - by snapCount. In order to prevent all of the machines in the quorum - from taking a snapshot at the same time, each ZooKeeper server - will take a snapshot when the number of transactions in the transaction log - reaches a runtime generated random value in the [snapCount/2+1, snapCount] - range.The default snapCount is 100,000.</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>zookeeper.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> - - -<dt> -<term>zookeeper.extendedTypesEnabled</term> -</dt> -<dd> -<p>(Java system property only: <strong>zookeeper.extendedTypesEnabled</strong>)</p> -<p> -<strong>New in 3.5.4, 3.6.0:</strong> Define to "true" to enable - extended features such as the creation of <a href="zookeeperProgrammers.html#TTL+Nodes">TTL Nodes</a>. - They are disabled by default. IMPORTANT: when enabled server IDs must - be less than 255 due to internal limitations. - </p> -</dd> - - -<dt> -<term>zookeeper.emulate353TTLNodes</term> -</dt> -<dd> -<p>(Java system property only: <strong>zookeeper.emulate353TTLNodes</strong>)</p> -<p> -<strong>New in 3.5.4, 3.6.0:</strong> Due to - <a href="https://issues.apache.org/jira/browse/ZOOKEEPER-2901";>ZOOKEEPER-2901</a> TTL nodes - created in version 3.5.3 are not supported in 3.5.4/3.6.0. However, a workaround is provided via the - zookeeper.emulate353TTLNodes system property. If you used TTL nodes in ZooKeeper 3.5.3 and need to maintain - compatibility set <strong>zookeeper.emulate353TTLNodes</strong> to "true" in addition to - <strong>zookeeper.extendedTypesEnabled</strong>. NOTE: due to the bug, server IDs - must be 127 or less. Additionally, the maximum support TTL value is 1099511627775 which is smaller - than what was allowed in 3.5.3 (1152921504606846975)</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> - - -<dt> -<term>standaloneEnabled</term> -</dt> -<dd> -<p>(No Java system property)</p> -<p> -<strong>New in 3.5.0:</strong> - When set to false, a single server can be started in replicated - mode, a lone participant can run with observers, and a cluster - can reconfigure down to one node, and up from one node. The - default is true for backwards compatibility. It can be set - using QuorumPeerConfig's setStandaloneEnabled method or by - adding "standaloneEnabled=false" or "standaloneEnabled=true" - to a server's config file. - </p> -</dd> - - -<dt> -<term>reconfigEnabled</term> -</dt> -<dd> -<p>(No Java system property)</p> -<p> -<strong>New in 3.5.3:</strong> - This controls the enabling or disabling of - <a href="zookeeperReconfig.html"> - Dynamic Reconfiguration</a> feature. When the feature - is enabled, users can perform reconfigure operations through - the ZooKeeper client API or through ZooKeeper command line tools - assuming users are authorized to perform such operations. - When the feature is disabled, no user, including the super user, - can perform a reconfiguration. Any attempt to reconfigure will return an error. - <strong>"reconfigEnabled"</strong> option can be set as - <strong>"reconfigEnabled=false"</strong> or - <strong>"reconfigEnabled=true"</strong> - to a server's config file, or using QuorumPeerConfig's - setReconfigEnabled method. The default value is false. - - If present, the value should be consistent across every server in - the entire ensemble. Setting the value as true on some servers and false - on other servers will cause inconsistent behavior depending on which server - is elected as leader. If the leader has a setting of - <strong>"reconfigEnabled=true"</strong>, then the ensemble - will have reconfig feature enabled. If the leader has a setting of - <strong>"reconfigEnabled=false"</strong>, then the ensemble - will have reconfig feature disabled. It is thus recommended to have a consistent - value for <strong>"reconfigEnabled"</strong> across servers - in the ensemble. - </p> -</dd> - - -<dt> -<term>4lw.commands.whitelist</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.4lw.commands.whitelist</strong>)</p> -<p> -<strong>New in 3.5.3:</strong> - A list of comma separated <a href="#sc_4lw">Four Letter Words</a> - commands that user wants to use. A valid Four Letter Words - command must be put in this list else ZooKeeper server will - not enable the command. - By default the whitelist only contains "srvr" command - which zkServer.sh uses. The rest of four letter word commands are disabled - by default. - </p> -<p>Here's an example of the configuration that enables stat, ruok, conf, and isro - command while disabling the rest of Four Letter Words command:</p> -<pre class="code"> - 4lw.commands.whitelist=stat, ruok, conf, isro - </pre> -<p>If you really need enable all four letter word commands by default, you can use - the asterisk option so you don't have to include every command one by one in the list. - As an example, this will enable all four letter word commands: - </p> -<pre class="code"> - 4lw.commands.whitelist=* - </pre> -</dd> - - -<dt> -<term>tcpKeepAlive</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.tcpKeepAlive</strong>)</p> -<p> -<strong>New in 3.5.4:</strong> - Setting this to true sets the TCP keepAlive flag on the - sockets used by quorum members to perform elections. - This will allow for connections between quorum members to - remain up when there is network infrastructure that may - otherwise break them. Some NATs and firewalls may terminate - or lose state for long running or idle connections.</p> -<p> Enabling this option relies on OS level settings to work - properly, check your operating system's options regarding TCP - keepalive for more information. Defaults to - <strong>false</strong>. - </p> -</dd> - - -</dl> -<p></p> -<a name="sc_authOptions"></a> -<h4>Encryption, Authentication, Authorization Options</h4> -<p>The options in this section allow control over - encryption/authentication/authorization performed by the service.</p> -<dl> - -<dt> -<term>DigestAuthenticationProvider.superDigest</term> -</dt> -<dd> -<p>(Java system property: <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> - - -<dt> -<term>X509AuthenticationProvider.superUser</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.X509AuthenticationProvider.superUser</strong>)</p> -<p>The SSL-backed way to enable a ZooKeeper ensemble - administrator to access the znode hierarchy as a "super" user. - When this parameter is set to an X500 principal name, only an - authenticated client with that principal will be able to bypass - ACL checking and have full privileges to all znodes.</p> -</dd> - - -<dt> -<term>zookeeper.superUser</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.superUser</strong>)</p> -<p>Similar to <strong>zookeeper.X509AuthenticationProvider.superUser</strong> - but is generic for SASL based logins. It stores the name of - a user that can access the znode hierarchy as a "super" user. - </p> -</dd> - - -<dt> -<term>ssl.keyStore.location and ssl.keyStore.password</term> -</dt> -<dd> -<p>(Java system properties: <strong> - zookeeper.ssl.keyStore.location</strong> and <strong>zookeeper.ssl.keyStore.password</strong>)</p> -<p>Specifies the file path to a JKS containing the local - credentials to be used for SSL connections, and the - password to unlock the file.</p> -</dd> - - -<dt> -<term>ssl.trustStore.location and ssl.trustStore.password</term> -</dt> -<dd> -<p>(Java system properties: <strong> - zookeeper.ssl.trustStore.location</strong> and <strong>zookeeper.ssl.trustStore.password</strong>)</p> -<p>Specifies the file path to a JKS containing the remote - credentials to be used for SSL connections, and the - password to unlock the file.</p> -</dd> - - -<dt> -<term>ssl.authProvider</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.ssl.authProvider</strong>)</p> -<p>Specifies a subclass of <strong> - org.apache.zookeeper.auth.X509AuthenticationProvider</strong> - to use for secure client authentication. This is useful in - certificate key infrastructures that do not use JKS. It may be - necessary to extend <strong>javax.net.ssl.X509KeyManager - </strong> and <strong>javax.net.ssl.X509TrustManager</strong> - to get the desired behavior from the SSL stack. To configure the - ZooKeeper server to use the custom provider for authentication, - choose a scheme name for the custom AuthenticationProvider and - set the property <strong>zookeeper.authProvider.[scheme] - </strong> to the fully-qualified class name of the custom - implementation. This will load the provider into the ProviderRegistry. - Then set this property <strong> - zookeeper.ssl.authProvider=[scheme]</strong> and that provider - will be used for secure authentication.</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="Disabling+data+directory+autocreation"></a> -<h4>Disabling data directory autocreation</h4> -<p> -<strong>New in 3.5:</strong> The default - behavior of a ZooKeeper server is to automatically create the - data directory (specified in the configuration file) when - started if that directory does not already exist. This can be - inconvenient and even dangerous in some cases. Take the case - where a configuration change is made to a running server, - wherein the <strong>dataDir</strong> parameter - is accidentally changed. When the ZooKeeper server is - restarted it will create this non-existent directory and begin - serving - with an empty znode namespace. This scenario can - result in an effective "split brain" situation (i.e. data in - both the new invalid directory and the original valid data - store). As such is would be good to have an option to turn off - this autocreate behavior. In general for production - environments this should be done, unfortunately however the - default legacy behavior cannot be changed at this point and - therefore this must be done on a case by case basis. This is - left to users and to packagers of ZooKeeper distributions. - </p> -<p>When running <strong>zkServer.sh</strong> autocreate can be disabled - by setting the environment variable <strong>ZOO_DATADIR_AUTOCREATE_DISABLE</strong> to 1. - When running ZooKeeper servers directly from class files this - can be accomplished by setting <strong>zookeeper.datadir.autocreate=false</strong> on - the java command line, i.e. <strong>-Dzookeeper.datadir.autocreate=false</strong> - -</p> -<p>When this feature is disabled, and the ZooKeeper server - determines that the required directories do not exist it will - generate an error and refuse to start. - </p> -<p>A new script <strong>zkServer-initialize.sh</strong> is provided to - support this new feature. If autocreate is disabled it is - necessary for the user to first install ZooKeeper, then create - the data directory (and potentially txnlog directory), and - then start the server. Otherwise as mentioned in the previous - paragraph the server will not start. Running <strong>zkServer-initialize.sh</strong> will create the - required directories, and optionally setup the myid file - (optional command line parameter). This script can be used - even if the autocreate feature itself is not used, and will - likely be of use to users as this (setup, including creation - of the myid file) has been an issue for users in the past. - Note that this script ensures the data directories exist only, - it does not create a config file, but rather requires a config - file to be available in order to execute. - </p> -<a name="sc_performance_options"></a> -<h4>Performance Tuning Options</h4> -<p> -<strong>New in 3.5.0:</strong> Several subsystems have been reworked - to improve read throughput. This includes multi-threading of the NIO communication subsystem and - request processing pipeline (Commit Processor). NIO is the default client/server communication - subsystem. Its threading model comprises 1 acceptor thread, 1-N selector threads and 0-M - socket I/O worker threads. In the request processing pipeline the system can be configured - to process multiple read request at once while maintaining the same consistency guarantee - (same-session read-after-write). The Commit Processor threading model comprises 1 main - thread and 0-N worker threads. - </p> -<p> - The default values are aimed at maximizing read throughput on a dedicated ZooKeeper machine. - Both subsystems need to have sufficient amount of threads to achieve peak read throughput. - </p> -<dl> - - -<dt> -<term>zookeeper.nio.numSelectorThreads</term> -</dt> -<dd> -<p>(Java system property only: <strong>zookeeper.nio.numSelectorThreads</strong>) - </p> -<p> -<strong>New in 3.5.0:</strong> - Number of NIO selector threads. At least 1 selector thread required. - It is recommended to use more than one selector for large numbers - of client connections. The default value is sqrt( number of cpu cores / 2 ). - </p> -</dd> - - -<dt> -<term>zookeeper.nio.numWorkerThreads</term> -</dt> -<dd> -<p>(Java system property only: <strong>zookeeper.nio.numWorkerThreads</strong>) - </p> -<p> -<strong>New in 3.5.0:</strong> - Number of NIO worker threads. If configured with 0 worker threads, the selector threads - do the socket I/O directly. The default value is 2 times the number of cpu cores. - </p> -</dd> - - -<dt> -<term>zookeeper.commitProcessor.numWorkerThreads</term> -</dt> -<dd> -<p>(Java system property only: <strong>zookeeper.commitProcessor.numWorkerThreads</strong>) - </p> -<p> -<strong>New in 3.5.0:</strong> - Number of Commit Processor worker threads. If configured with 0 worker threads, the main thread - will process the request directly. The default value is the number of cpu cores. - </p> -</dd> - - -<dt> -<term>znode.container.checkIntervalMs</term> -</dt> -<dd> -<p>(Java system property only)</p> -<p> -<strong>New in 3.5.1:</strong> The - time interval in milliseconds for each check of candidate container - and ttl nodes. Default is "60000".</p> -</dd> - - -<dt> -<term>znode.container.maxPerMinute</term> -</dt> -<dd> -<p>(Java system property only)</p> -<p> -<strong>New in 3.5.1:</strong> The - maximum number of container nodes that can be deleted per - minute. This prevents herding during container deletion. - Default is "10000".</p> -</dd> - -</dl> -<a name="Communication+using+the+Netty+framework"></a> -<h4>Communication using the Netty framework</h4> -<p> -<a href="http://netty.io";>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>In versions 3.5+, a ZooKeeper server can use Netty - instead of NIO (default option) by setting the environment - variable <strong>zookeeper.serverCnxnFactory</strong> - to <strong>org.apache.zookeeper.server.NettyServerCnxnFactory</strong>; - for the client, set <strong>zookeeper.clientCnxnSocket</strong> - to <strong>org.apache.zookeeper.ClientCnxnSocketNetty</strong>. - </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_adminserver_config"></a> -<h4>AdminServer configuration</h4> -<p> -<strong>New in 3.5.0:</strong> The following - options are used to configure the <a href="#sc_adminserver">AdminServer</a>.</p> -<dl> - -<dt> -<term>admin.enableServer</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.admin.enableServer</strong>)</p> -<p>Set to "false" to disable the AdminServer. By default the - AdminServer is enabled.</p> -</dd> - - -<dt> -<term>admin.serverAddress</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.admin.serverAddress</strong>)</p> -<p>The address the embedded Jetty server listens on. Defaults to 0.0.0.0.</p> -</dd> - - -<dt> -<term>admin.serverPort</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.admin.serverPort</strong>)</p> -<p>The port the embedded Jetty server listens on. Defaults to 8080.</p> -</dd> - - -<dt> -<term>admin.idleTimeout</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.admin.idleTimeout</strong>)</p> -<p>Set the maximum idle time in milliseconds that a connection can wait - before sending or receiving data. Defaults to 30000 ms.</p> -</dd> - - - -<dt> -<term>admin.commandURL</term> -</dt> -<dd> -<p>(Java system property: <strong>zookeeper.admin.commandURL</strong>)</p> -<p>The URL for listing and issuing commands relative to the - root URL. Defaults to "/commands".</p> -</dd> - -</dl> -<a name="sc_zkCommands"></a> -<h3 class="h4">ZooKeeper Commands</h3> -<a name="sc_4lw"></a> -<h4>The Four Letter Words</h4> -<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> -<p> -<strong>New in 3.5.3:</strong> - Four Letter Words need to be explicitly white listed before using. - Please refer <strong>4lw.commands.whitelist</strong> - described in <a href="#sc_clusterOptions"> - cluster configuration section</a> for details. - Moving forward, Four Letter Words will be deprecated, please use - <a href="#sc_adminserver">AdminServer</a> instead. - </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>dirs</term> -</dt> -<dd> -<p> -<strong>New in 3.5.1:</strong> - Shows the total size of snapshot and log files in bytes - </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_num_alive_connections 1 - 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 - zk_last_proposal_size 23 - zk_min_proposal_size 23 - zk_max_proposal_size 64 - </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> - - -<dt> -<term>isro</term> -</dt> -<dd> -<p> -<strong>New in 3.4.0:</strong> Tests if - server is running in read-only mode. The server will respond with - "ro" if in read-only mode or "rw" if not in read-only mode.</p> -</dd> - - -<dt> -<term>gtmk</term> -</dt> -<dd> -<p>Gets the current trace mask as a 64-bit signed long value in - decimal format. See <span class="codefrag command">stmk</span> for an explanation of - the possible values.</p> -</dd> - - -<dt> -<term>stmk</term> -</dt> -<dd> -<p>Sets the current trace mask. The trace mask is 64 bits, - where each bit enables or disables a specific category of trace - logging on the server. Log4J must be configured to enable - <span class="codefrag command">TRACE</span> level first in order to see trace logging - messages. The bits of the trace mask correspond to the following - trace logging categories.</p> -<table class="ForrestTable" cellspacing="1" cellpadding="4"> -<caption>Trace Mask Bit Values</caption> - -<title>Trace Mask Bit Values</title> - - -<tr> - -<td>0b0000000000</td> - <td>Unused, reserved for future use.</td> - -</tr> - -<tr> - -<td>0b0000000010</td> - <td>Logs client requests, excluding ping - requests.</td> - -</tr> - -<tr> - -<td>0b0000000100</td> - <td>Unused, reserved for future use.</td> - -</tr> - -<tr> - -<td>0b0000001000</td> - <td>Logs client ping requests.</td> - -</tr> - -<tr> - -<td>0b0000010000</td> - <td>Logs packets received from the quorum peer that is - the current leader, excluding ping requests.</td> - -</tr> - -<tr> - -<td>0b0000100000</td> - <td>Logs addition, removal and validation of client - sessions.</td> - -</tr> - -<tr> - -<td>0b0001000000</td> - <td>Logs delivery of watch events to client - sessions.</td> - -</tr> - -<tr> - -<td>0b0010000000</td> - <td>Logs ping packets received from the quorum peer - that is the current leader.</td> - -</tr> - -<tr> - -<td>0b0100000000</td> - <td>Unused, reserved for future use.</td> - -</tr> - -<tr> - -<td>0b1000000000</td> - <td>Unused, reserved for future use.</td> - -</tr> - - -</table> -<p>All remaining bits in the 64-bit value are unused and - reserved for future use. Multiple trace logging categories are - specified by calculating the bitwise OR of the documented values. - The default trace mask is 0b0100110010. Thus, by default, trace - logging includes client requests, packets received from the - leader and sessions.</p> -<p>To set a different trace mask, send a request containing the - <span class="codefrag command">stmk</span> four-letter word followed by the trace - mask represented as a 64-bit signed long value. This example uses - the Perl <span class="codefrag command">pack</span> function to construct a trace - mask that enables all trace logging categories described above and - convert it to a 64-bit signed long value with big-endian byte - order. The result is appended to <span class="codefrag command">stmk</span> and sent - to the server using netcat. The server responds with the new - trace mask in decimal format.</p> -<pre class="code">$ perl -e "print 'stmk', pack('q>', 0b0011111010)" | nc localhost 2181 -250 - </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_adminserver"></a> -<h4>The AdminServer</h4> -<p> -<strong>New in 3.5.0: </strong>The AdminServer is - an embedded Jetty server that provides an HTTP interface to the four - letter word commands. By default, the server is started on port 8080, - and commands are issued by going to the URL "/commands/[command name]", - e.g., http://localhost:8080/commands/stat. The command response is - returned as JSON. Unlike the original protocol, commands are not - restricted to four-letter names, and commands can have multiple names; - for instance, "stmk" can also be referred to as "set_trace_mask". To - view a list of all available commands, point a browser to the URL - /commands (e.g., http://localhost:8080/commands). See the <a href="#sc_adminserver_config">AdminServer configuration options</a> - for how to change the port and URLs.</p> -<p>The AdminServer is enabled by default, but can be disabled by either:</p> -<ul> - -<li> -<p>Setting the zookeeper.admin.enableServer system - property to false.</p> -</li> - -<li> -<p>Removing Jetty from the classpath. (This option is - useful if you would like to override ZooKeeper's jetty - dependency.)</p> -</li> - -</ul> -<p>Note that the TCP four letter word interface is still available if - the AdminServer is disabled.</p> -<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 when the number of transactions written to the - current log file reaches a (variable) threshold. The threshold is - computed using the same parameter which influences the frequency of - snapshotting (see snapCount above). 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 l
<TRUNCATED> http://git-wip-us.apache.org/repos/asf/zookeeper/blob/ab59048a/docs/zookeeperAdmin.pdf ---------------------------------------------------------------------- diff --git a/docs/zookeeperAdmin.pdf b/docs/zookeeperAdmin.pdf deleted file mode 100644 index 3c81835..0000000 Binary files a/docs/zookeeperAdmin.pdf and /dev/null differ
