Modified: helix/site-content/0.9.9-docs/tutorial_throttling.html URL: http://svn.apache.org/viewvc/helix/site-content/0.9.9-docs/tutorial_throttling.html?rev=1900184&r1=1900183&r2=1900184&view=diff ============================================================================== --- helix/site-content/0.9.9-docs/tutorial_throttling.html (original) +++ helix/site-content/0.9.9-docs/tutorial_throttling.html Sat Apr 23 04:22:15 2022 @@ -1,200 +1,190 @@ - <!DOCTYPE html> + + <!-- - Generated by Apache Maven Doxia at 2022-04-23 - Rendered using Maven Reflow Skin 1.0.0 (http://andriusvelykis.github.com/reflow-maven-skin) + | Generated by Apache Maven Doxia Site Renderer 1.11.1 from src/site/markdown/tutorial_throttling.md at 2022-04-23 + | Rendered using Apache Maven Fluido Skin 1.11.0-SNAPSHOT +--> +<html xmlns="http://www.w3.org/1999/xhtml"; lang="en"> + <head> + <meta charset="UTF-8" /> + <meta name="viewport" content="width=device-width, initial-scale=1" /> + <meta name="generator" content="Apache Maven Doxia Site Renderer 1.11.1" /> + <title>Apache Helix – Tutorial - Throttling</title> + <link rel="stylesheet" href="./css/apache-maven-fluido-1.11.0-SNAPSHOT.min.css" /> + <link rel="stylesheet" href="./css/site.css" /> + <link rel="stylesheet" href="./css/print.css" media="print" /> + <script src="./js/apache-maven-fluido-1.11.0-SNAPSHOT.min.js"></script> +<script type="text/javascript"> + + var _gaq = _gaq || []; + _gaq.push(['_setAccount', 'UA-3211522-12']); + _gaq.push(['_trackPageview']); + + (function() { + var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; + ga.src = ('https:' == document.location.protocol ? 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All Rights Reserved.</p> - <p><a href="http://github.com/andriusvelykis/reflow-maven-skin"; title="Reflow Maven skin">Reflow Maven skin</a> by <a href="http://andrius.velykis.lt"; target="_blank" title="Andrius Velykis">Andrius Velykis</a>.</p> - </div> - </div> - </div> - - <!-- Le javascript - ================================================== --> - <!-- Placed at the end of the document so the pages load faster --> - - <!-- Fallback jQuery loading from Google CDN: - http://stackoverflow.com/questions/1014203/best-way-to-use-googles-hosted-jquery-but-fall-back-to-my-hosted-library-on-go --> - <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js";></script> - <script type="text/javascript"> - if (typeof jQuery == 'undefined') - { - document.write(unescape("%3Cscript src='./js/jquery-1.8.3.min.js' type='text/javascript'%3E%3C/script%3E")); - } - </script> - - <script src="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.2.2/js/bootstrap.min.js";></script> - <script src="./js/lightbox.js"></script> - <script src="./js/jquery.smooth-scroll.min.js"></script> - <!-- back button support for smooth scroll --> - <script src="./js/jquery.ba-bbq.min.js"></script> - - <script src="./js/reflow-skin.js"></script> - - </body> +<section> +<h2><a name="Helix_Tutorial:_Throttling"></a><a href="./Tutorial.html">Helix Tutorial</a>: Throttling</h2> +<p>In this chapter, we'll learn how to control the parallel execution of cluster tasks. Only a centralized cluster manager with global knowledge (i.e. Helix) is capable of coordinating this decision.</p><section> +<h3><a name="Throttling"></a>Throttling</h3> +<p>Since all state changes in the system are triggered through transitions, Helix can control the number of transitions that can happen in parallel. Some of the transitions may be lightweight, but some might involve moving data, which is quite expensive from a network and IOPS perspective.</p> +<p>Helix allows applications to set a threshold on transitions. The threshold can be set at multiple scopes:</p> +<ul> + +<li>MessageType e.g STATE_TRANSITION</li> +<li>TransitionType e.g SLAVE-MASTER</li> +<li>Resource e.g database</li> +<li>Node i.e per-node maximum transitions in parallel</li> +</ul></section></section> + </main> + </div> + </div> + <hr/> + <footer> + <div class="container-fluid"> + <div class="row-fluid"> +<div class="row span16"><div>Apache Helix, Apache, the Apache feather logo, and the Apache Helix project logos are trademarks of The Apache Software Foundation. + All other marks mentioned may be trademarks or registered trademarks of their respective owners.</div> + <a href="https://helix.apache.org/0.9.9-docs/privacy-policy.html";>Privacy Policy</a> + </div> + </div> + </div> + </footer> +<script> + if(anchors) { + anchors.add(); + } +</script> + </body> </html> \ No newline at end of file
Modified: helix/site-content/0.9.9-docs/tutorial_ui.html URL: http://svn.apache.org/viewvc/helix/site-content/0.9.9-docs/tutorial_ui.html?rev=1900184&r1=1900183&r2=1900184&view=diff ============================================================================== --- helix/site-content/0.9.9-docs/tutorial_ui.html (original) +++ helix/site-content/0.9.9-docs/tutorial_ui.html Sat Apr 23 04:22:15 2022 @@ -1,200 +1,254 @@ - <!DOCTYPE html> + + <!-- - Generated by Apache Maven Doxia at 2022-04-23 - Rendered using Maven Reflow Skin 1.0.0 (http://andriusvelykis.github.com/reflow-maven-skin) + | Generated by Apache Maven Doxia Site Renderer 1.11.1 from src/site/markdown/tutorial_ui.md at 2022-04-23 + | Rendered using Apache Maven Fluido Skin 1.11.0-SNAPSHOT +--> +<html xmlns="http://www.w3.org/1999/xhtml"; lang="en"> + <head> + <meta charset="UTF-8" /> + <meta name="viewport" content="width=device-width, initial-scale=1" /> + <meta name="generator" content="Apache Maven Doxia Site Renderer 1.11.1" /> + <title>Apache Helix – Tutorial - Helix UI Setup</title> + <link rel="stylesheet" href="./css/apache-maven-fluido-1.11.0-SNAPSHOT.min.css" /> + <link rel="stylesheet" href="./css/site.css" /> + <link rel="stylesheet" href="./css/print.css" media="print" /> + <script src="./js/apache-maven-fluido-1.11.0-SNAPSHOT.min.js"></script> +<script type="text/javascript"> + + var _gaq = _gaq || []; + _gaq.push(['_setAccount', 'UA-3211522-12']); + _gaq.push(['_trackPageview']); + + (function() { + var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; + ga.src = ('https:' == document.location.protocol ? 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All Rights Reserved.</p> - <p><a href="http://github.com/andriusvelykis/reflow-maven-skin"; title="Reflow Maven skin">Reflow Maven skin</a> by <a href="http://andrius.velykis.lt"; target="_blank" title="Andrius Velykis">Andrius Velykis</a>.</p> - </div> - </div> - </div> - - <!-- Le javascript - ================================================== --> - <!-- Placed at the end of the document so the pages load faster --> - - <!-- Fallback jQuery loading from Google CDN: - http://stackoverflow.com/questions/1014203/best-way-to-use-googles-hosted-jquery-but-fall-back-to-my-hosted-library-on-go --> - <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js";></script> - <script type="text/javascript"> - if (typeof jQuery == 'undefined') - { - document.write(unescape("%3Cscript src='./js/jquery-1.8.3.min.js' type='text/javascript'%3E%3C/script%3E")); - } - </script> - - <script src="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.2.2/js/bootstrap.min.js";></script> - <script src="./js/lightbox.js"></script> - <script src="./js/jquery.smooth-scroll.min.js"></script> - <!-- back button support for smooth scroll --> - <script src="./js/jquery.ba-bbq.min.js"></script> - - <script src="./js/reflow-skin.js"></script> - - </body> +<section> +<h2><a name="Helix_Tutorial:_Helix_UI_Setup"></a><a href="./Tutorial.html">Helix Tutorial</a>: Helix UI Setup</h2> +<p>Helix now provides a modern web user interface for users to manage Helix clusters in a more convenient way (aka Helix UI). Currently the following features are supported via Helix UI:</p> +<ul> + +<li>View all Helix clusters exposed by Helix REST service</li> +<li>View detailed cluster information</li> +<li>View resources / instances in a Helix cluster</li> +<li>View partition placement and health status in a resource</li> +<li>Create new Helix clusters</li> +<li>Enable / Disable a cluster / resource / instance</li> +<li>Add an instance into a Helix cluster</li> +</ul><section> +<h3><a name="Prerequisites"></a>Prerequisites</h3> +<p>Since Helix UI is talking with Helix REST service to manage Helix clusters, a well deployed Helix REST service is required and necessary. Please refer to this tutorial to setup a functional Helix REST service: <a href="./tutorial_rest_service.html">Helix REST Service 2.0</a>.</p></section><section> +<h3><a name="Installation"></a>Installation</h3> +<p>To get and run Helix UI locally, simply use the following command lines:</p> + +<div class="source"><pre class="prettyprint"><code>git clone https://git-wip-us.apache.org/repos/asf/helix.git +cd helix/helix-front +git checkout tags/helix-0.9.9 +../build +cd target/helix-front-pkg/bin +chmod +x *.sh +</code></pre></div></section><section> +<h3><a name="Configuration"></a>Configuration</h3> +<p>Helix UI does not need any configuration if you have started Helix REST service without specifying a port ( Helix REST service will be serving through <a class="externalLink" href="http://localhost:8100/admin/v2";>http://localhost:8100/admin/v2</a> ). If you have specified a customized port or you need to wire in additional REST services, please navigate to <code>../dist/server/config.js</code> and edit the following section accordingly:</p> + +<div class="source"><pre class="prettyprint"><code>... +exports.HELIX_ENDPOINTS = { + <service nickname>: [ + { + <nickname of REST endpoint>: '<REST endpoint url>' + } + ] +}; +... +</code></pre></div> +<p>For example, if you have multiple Helix REST services deployed (all listening on port 12345), and you want to divide them into two services, and each service will contain two groups (e.g. staging and production), and each group will contain two fabrics as well, you may configure the above section like this:</p> + +<div class="source"><pre class="prettyprint"><code>... +exports.HELIX_ENDPOINTS = { + service1: [ + { + staging1: 'http://staging1.service1.com:12345/admin/v2', + staging2: 'http://staging2.service1.com:12345/admin/v2' + }, + { + production1: 'http://production1.service1.com:12345/admin/v2', + production2: 'http://production2.service1.com:12345/admin/v2' + } + ], + service2: [ + { + staging1: 'http://staging1.service2.com:12345/admin/v2', + staging2: 'http://staging2.service2.com:12345/admin/v2' + }, + { + production1: 'http://production1.service2.com:12345/admin/v2', + production2: 'http://production2.service2.com:12345/admin/v2' + } + ] +}; +... + +</code></pre></div></section><section> +<h3><a name="Launch_Helix_UI"></a>Launch Helix UI</h3> + +<div class="source"><pre class="prettyprint"><code>./start-helix-ui.sh +</code></pre></div> +<p>Helix UI will be listening on your port <code>3000</code> by default. Just use any browser to navigate to <a class="externalLink" href="http://localhost:3000";>http://localhost:3000</a> to get started.</p></section><section> +<h3><a name="Introduction"></a>Introduction</h3> +<p>The primary UI will look like this:</p> +<p><img src="./images/UIScreenshot.png" alt="UI Screenshot" /></p> +<p>The left side is the cluster list, and the right side is the detailed cluster view if you click one on the left. You will find resource list, workflow list and instance list of the cluster as well as the cluster configurations.</p> +<p>When navigating into a single resource, Helix UI will show the partition placement with comparison of idealStates and externalViews like this:</p> +<p><img src="./images/UIScreenshot2.png" alt="UI Screenshot" /></p></section></section> + </main> + </div> + </div> + <hr/> + <footer> + <div class="container-fluid"> + <div class="row-fluid"> +<div class="row span16"><div>Apache Helix, Apache, the Apache feather logo, and the Apache Helix project logos are trademarks of The Apache Software Foundation. + All other marks mentioned may be trademarks or registered trademarks of their respective owners.</div> + <a href="https://helix.apache.org/0.9.9-docs/privacy-policy.html";>Privacy Policy</a> + </div> + </div> + </div> + </footer> +<script> + if(anchors) { + anchors.add(); + } +</script> + </body> </html> \ No newline at end of file Modified: helix/site-content/0.9.9-docs/tutorial_user_content_store.html URL: http://svn.apache.org/viewvc/helix/site-content/0.9.9-docs/tutorial_user_content_store.html?rev=1900184&r1=1900183&r2=1900184&view=diff ============================================================================== --- helix/site-content/0.9.9-docs/tutorial_user_content_store.html (original) +++ helix/site-content/0.9.9-docs/tutorial_user_content_store.html Sat Apr 23 04:22:15 2022 @@ -1,200 +1,221 @@ - <!DOCTYPE html> + + <!-- - Generated by Apache Maven Doxia at 2022-04-23 - Rendered using Maven Reflow Skin 1.0.0 (http://andriusvelykis.github.com/reflow-maven-skin) + | Generated by Apache Maven Doxia Site Renderer 1.11.1 from src/site/markdown/tutorial_user_content_store.md at 2022-04-23 + | Rendered using Apache Maven Fluido Skin 1.11.0-SNAPSHOT +--> +<html xmlns="http://www.w3.org/1999/xhtml"; lang="en"> + <head> + <meta charset="UTF-8" /> + <meta name="viewport" content="width=device-width, initial-scale=1" /> + <meta name="generator" content="Apache Maven Doxia Site Renderer 1.11.1" /> + <title>Apache Helix – Tutorial - User Defined Content Store for Tasks</title> + <link rel="stylesheet" href="./css/apache-maven-fluido-1.11.0-SNAPSHOT.min.css" /> + <link rel="stylesheet" href="./css/site.css" /> + <link rel="stylesheet" href="./css/print.css" media="print" /> + <script src="./js/apache-maven-fluido-1.11.0-SNAPSHOT.min.js"></script> +<script type="text/javascript"> + + var _gaq = _gaq || []; + _gaq.push(['_setAccount', 'UA-3211522-12']); + _gaq.push(['_trackPageview']); + + (function() { + var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; + ga.src = ('https:' == document.location.protocol ? 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All Rights Reserved.</p> - <p><a href="http://github.com/andriusvelykis/reflow-maven-skin"; title="Reflow Maven skin">Reflow Maven skin</a> by <a href="http://andrius.velykis.lt"; target="_blank" title="Andrius Velykis">Andrius Velykis</a>.</p> - </div> - </div> - </div> - - <!-- Le javascript - ================================================== --> - <!-- Placed at the end of the document so the pages load faster --> - - <!-- Fallback jQuery loading from Google CDN: - http://stackoverflow.com/questions/1014203/best-way-to-use-googles-hosted-jquery-but-fall-back-to-my-hosted-library-on-go --> - <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js";></script> - <script type="text/javascript"> - if (typeof jQuery == 'undefined') - { - document.write(unescape("%3Cscript src='./js/jquery-1.8.3.min.js' type='text/javascript'%3E%3C/script%3E")); - } - </script> - - <script src="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.2.2/js/bootstrap.min.js";></script> - <script src="./js/lightbox.js"></script> - <script src="./js/jquery.smooth-scroll.min.js"></script> - <!-- back button support for smooth scroll --> - <script src="./js/jquery.ba-bbq.min.js"></script> - - <script src="./js/reflow-skin.js"></script> - - </body> +<section> +<h2><a name="Helix_Tutorial:_User_Defined_Content_Store_for_Tasks"></a><a href="./Tutorial.html">Helix Tutorial</a>: User Defined Content Store for Tasks</h2> +<p>The purpose of user defined content store is to provide an easy use feature for some task dedicated meta temporary store. +In this chapter, we'll learn how to implement and use content store in the user defined tasks.</p><section> +<h3><a name="Content_Store_Implementation"></a>Content Store Implementation</h3> +<p>Extends abstract class UserContentStore.</p> + +<div class="source"><pre class="prettyprint"><code>private static class ContentStoreTask extends UserContentStore implements Task { + @Override public TaskResult run() { + ... + } + @Override public void cancel() { + ... + } +} +</code></pre></div> +<p>The default methods support 3 types of scopes:</p> +<ol style="list-style-type: decimal"> + +<li>WORKFLOW: Define the content store in workflow level</li> +<li>JOB: Define the content store in job level</li> +<li>TASK: Define the content store in task level</li> +</ol></section><section> +<h3><a name="Content_Store_Usage"></a>Content Store Usage</h3> +<p>Access content store in Task.run() method.</p> + +<div class="source"><pre class="prettyprint"><code> private static class ContentStoreTask extends UserContentStore implements Task { + @Override public TaskResult run() { + // put values into the store + putUserContent("ContentTest", "Value1", Scope.JOB); + putUserContent("ContentTest", "Value2", Scope.WORKFLOW); + putUserContent("ContentTest", "Value3", Scope.TASK); + + // get the values with the same key in the different scopes + if (!getUserContent("ContentTest", Scope.JOB).equals("Value1") || + !getUserContent("ContentTest", Scope.WORKFLOW).equals("Value2") || + !getUserContent("ContentTest", Scope.TASK).equals("Value3")) { + return new TaskResult(TaskResult.Status.FAILED, null); + } + + return new TaskResult(TaskResult.Status.COMPLETED, null); + } + } +</code></pre></div></section></section> + </main> + </div> + </div> + <hr/> + <footer> + <div class="container-fluid"> + <div class="row-fluid"> +<div class="row span16"><div>Apache Helix, Apache, the Apache feather logo, and the Apache Helix project logos are trademarks of The Apache Software Foundation. + All other marks mentioned may be trademarks or registered trademarks of their respective owners.</div> + <a href="https://helix.apache.org/0.9.9-docs/privacy-policy.html";>Privacy Policy</a> + </div> + </div> + </div> + </footer> +<script> + if(anchors) { + anchors.add(); 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All Rights Reserved.</p> - <p><a href="http://github.com/andriusvelykis/reflow-maven-skin"; title="Reflow Maven skin">Reflow Maven skin</a> by <a href="http://andrius.velykis.lt"; target="_blank" title="Andrius Velykis">Andrius Velykis</a>.</p> - </div> - </div> - </div> - - <!-- Le javascript - ================================================== --> - <!-- Placed at the end of the document so the pages load faster --> - - <!-- Fallback jQuery loading from Google CDN: - http://stackoverflow.com/questions/1014203/best-way-to-use-googles-hosted-jquery-but-fall-back-to-my-hosted-library-on-go --> - <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js";></script> - <script type="text/javascript"> - if (typeof jQuery == 'undefined') - { - document.write(unescape("%3Cscript src='./js/jquery-1.8.3.min.js' type='text/javascript'%3E%3C/script%3E")); - } - </script> - - <script src="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.2.2/js/bootstrap.min.js";></script> - <script src="./js/lightbox.js"></script> - <script src="./js/jquery.smooth-scroll.min.js"></script> - <!-- back button support for smooth scroll --> - <script src="./js/jquery.ba-bbq.min.js"></script> - - <script src="./js/reflow-skin.js"></script> - - </body> +<section> +<h2><a name="Helix_Tutorial:_User-Defined_Rebalancing"></a><a href="./Tutorial.html">Helix Tutorial</a>: User-Defined Rebalancing</h2> +<p>Even though Helix can compute both the location and the state of replicas internally using a default fully-automatic rebalancer, specific applications may require rebalancing strategies that optimize for different requirements. Thus, Helix allows applications to plug in arbitrary rebalancer algorithms that implement a provided interface. One of the main design goals of Helix is to provide maximum flexibility to any distributed application. Thus, it allows applications to fully implement the rebalancer, which is the core constraint solver in the system, if the application developer so chooses.</p> +<p>Whenever the state of the cluster changes, as is the case when participants join or leave the cluster, Helix automatically calls the rebalancer to compute a new mapping of all the replicas in the resource. When using a pluggable rebalancer, the only required step is to register it with Helix. Subsequently, no additional bootstrapping steps are necessary. Helix uses reflection to look up and load the class dynamically at runtime. As a result, it is also technically possible to change the rebalancing strategy used at any time.</p> +<p>The Rebalancer interface is as follows:</p> + +<div class="source"><pre class="prettyprint"><code>void init(HelixManager manager); + +IdealState computeNewIdealState(String resourceName, IdealState currentIdealState, + final CurrentStateOutput currentStateOutput, final ClusterDataCache clusterData); +</code></pre></div> +<p>The first parameter is the resource to rebalance, the second is pre-existing ideal mappings, the third is a snapshot of the actual placements and state assignments, and the fourth is a full cache of all of the cluster data available to Helix. Internally, Helix implements the same interface for its own rebalancing routines, so a user-defined rebalancer will be cognizant of the same information about the cluster as an internal implementation. Helix strives to provide applications the ability to implement algorithms that may require a large portion of the entire state of the cluster to make the best placement and state assignment decisions possible.</p> +<p>An IdealState is a full representation of the location of each replica of each partition of a given resource. This is a simple representation of the placement that the algorithm believes is the best possible. If the placement meets all defined constraints, this is what will become the actual state of the distributed system.</p><section> +<h3><a name="Specifying_a_Rebalancer"></a>Specifying a Rebalancer</h3> +<p>For implementations that set up the cluster through existing code, the following HelixAdmin calls will update the Rebalancer class:</p> + +<div class="source"><pre class="prettyprint"><code>IdealState idealState = helixAdmin.getResourceIdealState(clusterName, resourceName); +idealState.setRebalanceMode(RebalanceMode.USER_DEFINED); +idealState.setRebalancerClassName(className); +helixAdmin.setResourceIdealState(clusterName, resourceName, idealState); +</code></pre></div> +<p>There are two key fields to set to specify that a pluggable rebalancer should be used. First, the rebalance mode should be set to USER_DEFINED, and second the rebalancer class name should be set to a class that implements Rebalancer and is within the scope of the project. The class name is a fully-qualified class name consisting of its package and its name. Without specification of the USER_DEFINED mode, the user-defined rebalancer class will not be used even if specified. Furthermore, Helix will not attempt to rebalance the resources through its standard routines if its mode is USER_DEFINED, regardless of whether or not a rebalancer class is registered.</p></section><section> +<h3><a name="Example"></a>Example</h3> +<p>In the next release (0.7.0), we will provide a full recipe of a user-defined rebalancer in action.</p> +<p>Consider the case where partitions are locks in a lock manager and 6 locks are to be distributed evenly to a set of participants, and only one participant can hold each lock. We can define a rebalancing algorithm that simply takes the modulus of the lock number and the number of participants to evenly distribute the locks across participants. Helix allows capping the number of partitions a participant can accept, but since locks are lightweight, we do not need to define a restriction in this case. The following is a succinct implementation of this algorithm.</p> + +<div class="source"><pre class="prettyprint"><code>@Override +IdealState computeNewIdealState(String resourceName, IdealState currentIdealState, + final CurrentStateOutput currentStateOutput, final ClusterDataCache clusterData) { + // Get the list of live participants in the cluster + List<String> liveParticipants = new ArrayList<String>(clusterData.getLiveInstances().keySet()); + + // Count the number of participants allowed to lock each lock (in this example, this is 1) + int lockHolders = Integer.parseInt(currentIdealState.getReplicas()); + + // Fairly assign the lock state to the participants using a simple mod-based sequential + // assignment. For instance, if each lock can be held by 3 participants, lock 0 would be held + // by participants (0, 1, 2), lock 1 would be held by (1, 2, 3), and so on, wrapping around the + // number of participants as necessary. + int i = 0; + for (String partition : currentIdealState.getPartitionSet()) { + List<String> preferenceList = new ArrayList<String>(); + for (int j = i; j < i + lockHolders; j++) { + int participantIndex = j % liveParticipants.size(); + String participant = liveParticipants.get(participantIndex); + // enforce that a participant can only have one instance of a given lock + if (!preferenceList.contains(participant)) { + preferenceList.add(participant); + } + } + currentIdealState.setPreferenceList(partition, preferenceList); + i++; + } + return assignment; +} +</code></pre></div> +<p>Here are the IdealState preference lists emitted by the user-defined rebalancer for a 3-participant system whenever there is a change to the set of participants.</p> +<ul> + +<li>Participant_A joins</li> +</ul> + +<div class="source"><pre class="prettyprint"><code>{ + "lock_0": ["Participant_A"], + "lock_1": ["Participant_A"], + "lock_2": ["Participant_A"], + "lock_3": ["Participant_A"], + "lock_4": ["Participant_A"], + "lock_5": ["Participant_A"], +} +</code></pre></div> +<p>A preference list is a mapping for each resource of partition to the participants serving each replica. The state model is a simple LOCKED/RELEASED model, so participant A holds all lock partitions in the LOCKED state.</p> +<ul> + +<li>Participant_B joins</li> +</ul> + +<div class="source"><pre class="prettyprint"><code>{ + "lock_0": ["Participant_A"], + "lock_1": ["Participant_B"], + "lock_2": ["Participant_A"], + "lock_3": ["Participant_B"], + "lock_4": ["Participant_A"], + "lock_5": ["Participant_B"], +} +</code></pre></div> +<p>Now that there are two participants, the simple mod-based function assigns every other lock to the second participant. On any system change, the rebalancer is invoked so that the application can define how to redistribute its resources.</p> +<ul> + +<li>Participant_C joins (steady state)</li> +</ul> + +<div class="source"><pre class="prettyprint"><code>{ + "lock_0": ["Participant_A"], + "lock_1": ["Participant_B"], + "lock_2": ["Participant_C"], + "lock_3": ["Participant_A"], + "lock_4": ["Participant_B"], + "lock_5": ["Participant_C"], +} +</code></pre></div> +<p>This is the steady state of the system. Notice that four of the six locks now have a different owner. That is because of the naïve modulus-based assignmemt approach used by the user-defined rebalancer. However, the interface is flexible enough to allow you to employ consistent hashing or any other scheme if minimal movement is a system requirement.</p> +<ul> + +<li>Participant_B fails</li> +</ul> + +<div class="source"><pre class="prettyprint"><code>{ + "lock_0": ["Participant_A"], + "lock_1": ["Participant_C"], + "lock_2": ["Participant_A"], + "lock_3": ["Participant_C"], + "lock_4": ["Participant_A"], + "lock_5": ["Participant_C"], +} +</code></pre></div> +<p>On any node failure, as in the case of node addition, the rebalancer is invoked automatically so that it can generate a new mapping as a response to the change. Helix ensures that the Rebalancer has the opportunity to reassign locks as required by the application.</p> +<ul> + +<li>Participant_B (or the replacement for the original Participant_B) rejoins</li> +</ul> + +<div class="source"><pre class="prettyprint"><code>{ + "lock_0": ["Participant_A"], + "lock_1": ["Participant_B"], + "lock_2": ["Participant_C"], + "lock_3": ["Participant_A"], + "lock_4": ["Participant_B"], + "lock_5": ["Participant_C"], +} +</code></pre></div> +<p>The rebalancer was invoked once again and the resulting IdealState preference lists reflect the steady state.</p></section><section> +<h3><a name="Caveats"></a>Caveats</h3> +<ul> + +<li>The rebalancer class must be available at runtime, or else Helix will not attempt to rebalance at all</li> +<li>The Helix controller will only take into account the preference lists in the new IdealState for this release. In 0.7.0, Helix rebalancers will be able to compute the full resource assignment, including the states.</li> +<li>Helix does not currently persist the new IdealState computed by the user-defined rebalancer. However, the Helix property store is available for saving any computed state. In 0.7.0, Helix will persist the result of running the rebalancer.</li> +</ul></section></section> + </main> + </div> + </div> + <hr/> + <footer> + <div class="container-fluid"> + <div class="row-fluid"> +<div class="row span16"><div>Apache Helix, Apache, the Apache feather logo, and the Apache Helix project logos are trademarks of The Apache Software Foundation. + All other marks mentioned may be trademarks or registered trademarks of their respective owners.</div> + <a href="https://helix.apache.org/0.9.9-docs/privacy-policy.html";>Privacy Policy</a> + </div> + </div> + </div> + </footer> +<script> + if(anchors) { + anchors.add(); + } +</script> + </body> </html> \ No newline at end of file
