Added: helix/site-content/1.4.1-docs/tutorial_messaging.html URL: http://svn.apache.org/viewvc/helix/site-content/1.4.1-docs/tutorial_messaging.html?rev=1926553&view=auto ============================================================================== --- helix/site-content/1.4.1-docs/tutorial_messaging.html (added) +++ helix/site-content/1.4.1-docs/tutorial_messaging.html Wed Jun 18 18:28:44 2025 @@ -0,0 +1,295 @@ + +<!DOCTYPE html> + + + + + + +<!-- + Generated by Apache Maven Doxia at 2024-11-18 Rendered using Reflow Maven Skin 2.0.0 (https://olamy.github.io/reflow-maven-skin) +--> +<html xml:lang="en" lang="en"> + + <head> + <meta charset="UTF-8" /> + <title>Apache Helix – Tutorial - Messaging</title> + <meta name="viewport" content="width=device-width, initial-scale=1.0" /> + <meta name="description" content="" /> + <meta http-equiv="content-language" content="en" /> + + <link href="./css/bootstrap.min.css" rel="stylesheet" /> + <link href="./css/bootstrap-responsive.min.css" rel="stylesheet" /> + <link href="./css/docs.css" rel="stylesheet" /> + <link href="./css/reflow-skin.css" rel="stylesheet" /> + + + <link href="./css/lightbox.css" rel="stylesheet" /> + + <link href="./css/site.css" rel="stylesheet" /> + <link href="./css/print.css" rel="stylesheet" media="print" /> + + <!-- Le HTML5 shim, for IE6-8 support of HTML5 elements --> + <!--[if lt IE 9]> + <script src="./js/html5.js"></script> + <![endif]--> + + + + + + +<!-- Matomo --> +<script> + var _paq = window._paq = window._paq || []; 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id="bannerLeft"><img src="../images/helix-logo.jpg" alt='"''"' /></a> + <p class="lead">A cluster management framework for partitioned and replicated distributed resources</p> + </div> + <div class="pull-right"> + <a href="http://www.apache.org/"; id="bannerRight"><img src="../images/feather_small.gif" alt='"''"' /></a> + </div> + </div> + </div> + </div> + <div> + <ul class="breadcrumb"> + <li><a href="../" title="Apache Helix">Apache Helix</a></li> + <li class="divider">/</li> + <li><a href="./" title="Release 1.4.1">Release 1.4.1</a></li> + <li class="divider">/</li> + <li>Tutorial - Messaging</li> + <li class="publishDate version-date pull-right">Last Published: 2024-11-18</li> + </ul> + </div> + </header> + + <div class="main-body"> + <div class="row"> + <div class="span12"> + <div class="body-content"> +<!-- +Licensed to the Apache Software Foundation (ASF) under one +or more contributor license agreements. See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you under the Apache License, Version 2.0 (the +"License"); you may not use this file except in compliance +with the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, +software distributed under the License is distributed on an +"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +KIND, either express or implied. See the License for the +specific language governing permissions and limitations +under the License. +--> +<section> + <div class="page-header"> + <h2 id="Helix_Tutorial:_Messaging"><a href="./Tutorial.html">Helix Tutorial</a>: Messaging</h2> + </div> + <p>In this chapter, we'll learn about messaging, a convenient feature in Helix for sending messages between nodes of a cluster. This is an interesting feature that is quite useful in practice. It is common that nodes in a distributed system require a mechanism to interact with each other.</p> + <section> + <h3 id="Example:_Bootstrapping_a_Replica">Example: Bootstrapping a Replica</h3> + <p>Consider a search system where the index replica starts up and it does not have an index. A typical solution is to get the index from a common location, or to copy the index from another replica.</p> + <p>Helix provides a messaging API for intra-cluster communication between nodes in the system. This API provides a mechanism to specify the message recipient in terms of resource, partition, and state rather than specifying hostnames. Helix ensures that the message is delivered to all of the required recipients. In this particular use case, the instance can specify the recipient criteria as all replicas of the desired partition to bootstrap. Since Helix is aware of the global state of the system, it can send the message to the appropriate nodes. Once the nodes respond, Helix provides the bootstrapping replica with all the responses.</p> + <p>This is a very generic API and can also be used to schedule various periodic tasks in the cluster, such as data backups, log cleanup, etc. System Admins can also perform ad-hoc tasks, such as on-demand backups or a system command (such as rm -rf ;) across all nodes of the cluster</p> + <div class="source"> + <pre><code>ClusterMessagingService messagingService = manager.getMessagingService(); + +// Construct the Message +Message requestBackupUriRequest = new Message( + MessageType.USER_DEFINE_MSG, UUID.randomUUID().toString()); +requestBackupUriRequest + .setMsgSubType(BootstrapProcess.REQUEST_BOOTSTRAP_URL); +requestBackupUriRequest.setMsgState(MessageState.NEW); + +// Set the Recipient criteria: all nodes that satisfy the criteria will receive the message +Criteria recipientCriteria = new Criteria(); +recipientCriteria.setInstanceName("%"); +recipientCriteria.setRecipientInstanceType(InstanceType.PARTICIPANT); +recipientCriteria.setResource("MyDB"); +recipientCriteria.setPartition(""); + +// Should be processed only by process(es) that are active at the time of sending the message +// This means if the recipient is restarted after message is sent, it will not be processe. +recipientCriteria.setSessionSpecific(true); + +// wait for 30 seconds +int timeout = 30000; + +// the handler that will be invoked when any recipient responds to the message. +BootstrapReplyHandler responseHandler = new BootstrapReplyHandler(); + +// this will return only after all recipients respond or after timeout +int sentMessageCount = messagingService.sendAndWait(recipientCriteria, + requestBackupUriRequest, responseHandler, timeout); +</code></pre> + </div> + <p>See HelixManager.DefaultMessagingService in the <a class="externalLink" href="http://helix.apache.org/javadocs/1.4.1/reference/org/apache/helix/messaging/DefaultMessagingService.html";>Javadocs</a> for more information.</p> + </section> +</section> + </div> + </div> + </div> + </div> + + </div><!-- /container --> + + <!-- Footer + ================================================== --> + <footer class="well"> + <div class="container"> + <div class="row"> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Get Helix</li> + <li > + <a href="download.html" title="Download">Download</a> + </li> + <li > + <a href="Building.html" title="Building">Building</a> + </li> + <li > + <a href="releasenotes/release-1.4.1.html" title="Release Notes">Release Notes</a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Hands-On</li> + <li > + <a href="Quickstart.html" title="Quick Start">Quick Start</a> + </li> + <li > + <a href="Tutorial.html" title="Tutorial">Tutorial</a> + </li> + <li > + <a href="../javadocs/1.4.1" title="Javadocs">Javadocs</a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Recipes</li> + <li > + <a href="recipes/lock_manager.html" title="Distributed lock manager">Distributed lock manager</a> + </li> + <li > + <a href="recipes/rabbitmq_consumer_group.html" title="Rabbit MQ consumer group">Rabbit MQ consumer group</a> + </li> + <li > + <a href="recipes/rsync_replicated_file_store.html" title="Rsync replicated file store">Rsync replicated file store</a> + </li> + <li > + <a href="recipes/service_discovery.html" title="Service discovery">Service discovery</a> + </li> + <li > + <a href="recipes/task_dag_execution.html" title="Distributed task DAG execution">Distributed task DAG execution</a> + </li> + </ul> + </div> + </div> + </div> + </footer> + + <div class="container subfooter"> + <div class="row"> + <div class="span12"> + <p class="pull-right"><a href="#">Back to top</a></p> + <p class="copyright">Copyright ©2024 <a href="http://www.apache.org";>Apache Software Foundation</a>. 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Added: helix/site-content/1.4.1-docs/tutorial_participant.html URL: http://svn.apache.org/viewvc/helix/site-content/1.4.1-docs/tutorial_participant.html?rev=1926553&view=auto ============================================================================== --- helix/site-content/1.4.1-docs/tutorial_participant.html (added) +++ helix/site-content/1.4.1-docs/tutorial_participant.html Wed Jun 18 18:28:44 2025 @@ -0,0 +1,331 @@ + +<!DOCTYPE html> + + + + + + +<!-- + Generated by Apache Maven Doxia at 2024-11-18 Rendered using Reflow Maven Skin 2.0.0 (https://olamy.github.io/reflow-maven-skin) +--> +<html xml:lang="en" lang="en"> + + <head> + <meta charset="UTF-8" /> + <title>Apache Helix – Tutorial - Participant</title> + <meta name="viewport" content="width=device-width, initial-scale=1.0" /> + <meta name="description" content="" /> + <meta http-equiv="content-language" content="en" /> + + <link href="./css/bootstrap.min.css" rel="stylesheet" /> + <link href="./css/bootstrap-responsive.min.css" rel="stylesheet" /> + <link href="./css/docs.css" rel="stylesheet" /> + <link href="./css/reflow-skin.css" rel="stylesheet" /> + + + <link href="./css/lightbox.css" rel="stylesheet" /> + + <link href="./css/site.css" rel="stylesheet" /> + <link href="./css/print.css" rel="stylesheet" media="print" /> + + <!-- Le HTML5 shim, for IE6-8 support of HTML5 elements --> + <!--[if lt IE 9]> + <script src="./js/html5.js"></script> + <![endif]--> + + + + + + +<!-- Matomo --> +<script> + var _paq = window._paq = window._paq || []; 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id="bannerLeft"><img src="../images/helix-logo.jpg" alt='"''"' /></a> + <p class="lead">A cluster management framework for partitioned and replicated distributed resources</p> + </div> + <div class="pull-right"> + <a href="http://www.apache.org/"; id="bannerRight"><img src="../images/feather_small.gif" alt='"''"' /></a> + </div> + </div> + </div> + </div> + <div> + <ul class="breadcrumb"> + <li><a href="../" title="Apache Helix">Apache Helix</a></li> + <li class="divider">/</li> + <li><a href="./" title="Release 1.4.1">Release 1.4.1</a></li> + <li class="divider">/</li> + <li>Tutorial - Participant</li> + <li class="publishDate version-date pull-right">Last Published: 2024-11-18</li> + </ul> + </div> + </header> + + <div class="main-body"> + <div class="row"> + <div class="span12"> + <div class="body-content"> +<!-- +Licensed to the Apache Software Foundation (ASF) under one +or more contributor license agreements. See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you under the Apache License, Version 2.0 (the +"License"); you may not use this file except in compliance +with the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, +software distributed under the License is distributed on an +"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +KIND, either express or implied. See the License for the +specific language governing permissions and limitations +under the License. +--> +<section> + <div class="page-header"> + <h2 id="Helix_Tutorial:_Participant"><a href="./Tutorial.html">Helix Tutorial</a>: Participant</h2> + </div> + <p>In this chapter, we'll learn how to implement a <b>Participant</b>, which is a primary functional component of a distributed system.</p> + <section> + <h3 id="Start_a_Connection">Start a Connection</h3> + <p>The Helix manager is a common component that connects each system component with the controller.</p> + <p>It requires the following parameters:</p> + <ul> + <li>clusterName: A logical name to represent the group of nodes</li> + <li>instanceName: A logical name of the process creating the manager instance. Generally this is host:port</li> + <li>instanceType: Type of the process. This can be one of the following types, in this case, use PARTICIPANT + <ul> + <li>CONTROLLER: Process that controls the cluster, any number of controllers can be started but only one will be active at any given time</li> + <li>PARTICIPANT: Process that performs the actual task in the distributed system</li> + <li>SPECTATOR: Process that observes the changes in the cluster</li> + <li>ADMIN: To carry out system admin actions</li> + </ul> </li> + <li>zkConnectString: Connection string to ZooKeeper. This is of the form host1:port1,host2:port2,host3:port3</li> + </ul> + <p>After the Helix manager instance is created, the only thing that needs to be registered is the state model factory. The methods of the state model will be called when controller sends transitions to the participant. In this example, we'll use the OnlineOffline factory. Other options include:</p> + <ul> + <li>MasterSlaveStateModelFactory</li> + <li>LeaderStandbyStateModelFactory</li> + <li>BootstrapHandler</li> + </ul> + <div class="source"> + <pre><code>manager = HelixManagerFactory.getZKHelixManager(clusterName, + instanceName, + InstanceType.PARTICIPANT, + zkConnectString); +StateMachineEngine stateMach = manager.getStateMachineEngine(); + +//create a stateModelFactory that returns a statemodel object for each partition. +stateModelFactory = new OnlineOfflineStateModelFactory(); +stateMach.registerStateModelFactory(stateModelType, stateModelFactory); +manager.connect(); +</code></pre> + </div> + </section> + <section> + <h3 id="Example_State_Model_Factory">Example State Model Factory</h3> + <p>Helix doesn't know what it means to change from OFFLINE-->ONLINE or ONLINE-->OFFLINE. The following code snippet shows where you insert your system logic for these two state transitions.</p> + <div class="source"> + <pre><code>public class OnlineOfflineStateModelFactory extends + StateModelFactory<StateModel> { + @Override + public StateModel createNewStateModel(String stateUnitKey) { + OnlineOfflineStateModel stateModel = new OnlineOfflineStateModel(); + return stateModel; + } + @StateModelInfo(states = "{'OFFLINE','ONLINE'}", initialState = "OFFINE") + public static class OnlineOfflineStateModel extends StateModel { + @Transition(from = "OFFLINE", to = "ONLINE") + public void onBecomeOnlineFromOffline(Message message, + NotificationContext context) { + System.out.println("OnlineOfflineStateModel.onBecomeOnlineFromOffline()"); + + //////////////////////////////////////////////////////////////////////////////////////////////// + // Application logic to handle transition // + // For example, you might start a service, run initialization, etc // + //////////////////////////////////////////////////////////////////////////////////////////////// + } + + @Transition(from = "ONLINE", to = "OFFLINE") + public void onBecomeOfflineFromOnline(Message message, + NotificationContext context) { + System.out.println("OnlineOfflineStateModel.onBecomeOfflineFromOnline()"); + + //////////////////////////////////////////////////////////////////////////////////////////////// + // Application logic to handle transition // + // For example, you might shutdown a service, log this event, or change monitoring settings // + //////////////////////////////////////////////////////////////////////////////////////////////// + } + } +} +</code></pre> + </div> + </section> +</section> + </div> + </div> + </div> + </div> + + </div><!-- /container --> + + <!-- Footer + ================================================== --> + <footer class="well"> + <div class="container"> + <div class="row"> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Get Helix</li> + <li > + <a href="download.html" title="Download">Download</a> + </li> + <li > + <a href="Building.html" title="Building">Building</a> + </li> + <li > + <a href="releasenotes/release-1.4.1.html" title="Release Notes">Release Notes</a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Hands-On</li> + <li > + <a href="Quickstart.html" title="Quick Start">Quick Start</a> + </li> + <li > + <a href="Tutorial.html" title="Tutorial">Tutorial</a> + </li> + <li > + <a href="../javadocs/1.4.1" title="Javadocs">Javadocs</a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Recipes</li> + <li > + <a href="recipes/lock_manager.html" title="Distributed lock manager">Distributed lock manager</a> + </li> + <li > + <a href="recipes/rabbitmq_consumer_group.html" title="Rabbit MQ consumer group">Rabbit MQ consumer group</a> + </li> + <li > + <a href="recipes/rsync_replicated_file_store.html" title="Rsync replicated file store">Rsync replicated file store</a> + </li> + <li > + <a href="recipes/service_discovery.html" title="Service discovery">Service discovery</a> + </li> + <li > + <a href="recipes/task_dag_execution.html" title="Distributed task DAG execution">Distributed task DAG execution</a> + </li> + </ul> + </div> + </div> + </div> + </footer> + + <div class="container subfooter"> + <div class="row"> + <div class="span12"> + <p class="pull-right"><a href="#">Back to top</a></p> + <p class="copyright">Copyright ©2024 <a href="http://www.apache.org";>Apache Software Foundation</a>. 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id="bannerLeft"><img src="../images/helix-logo.jpg" alt='"''"' /></a> + <p class="lead">A cluster management framework for partitioned and replicated distributed resources</p> + </div> + <div class="pull-right"> + <a href="http://www.apache.org/"; id="bannerRight"><img src="../images/feather_small.gif" alt='"''"' /></a> + </div> + </div> + </div> + </div> + <div> + <ul class="breadcrumb"> + <li><a href="../" title="Apache Helix">Apache Helix</a></li> + <li class="divider">/</li> + <li><a href="./" title="Release 1.4.1">Release 1.4.1</a></li> + <li class="divider">/</li> + <li>Tutorial - Application Property Store</li> + <li class="publishDate version-date pull-right">Last Published: 2024-11-18</li> + </ul> + </div> + </header> + + <div class="main-body"> + <div class="row"> + <div class="span12"> + <div class="body-content"> +<!-- +Licensed to the Apache Software Foundation (ASF) under one +or more contributor license agreements. 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See the License for the +specific language governing permissions and limitations +under the License. +--> +<section> + <div class="page-header"> + <h2 id="Helix_Tutorial:_Application_Property_Store"><a href="./Tutorial.html">Helix Tutorial</a>: Application Property Store</h2> + </div> + <p>In this chapter, we'll learn how to use the application property store.</p> + <section> + <h3 id="Property_Store">Property Store</h3> + <p>It is common that an application needs support for distributed, shared data structures. Helix uses ZooKeeper to store the application data and hence provides notifications when the data changes.</p> + <p>While you could use ZooKeeper directly, Helix supports caching the data with a write-through cache. This is far more efficient than reading from ZooKeeper for every access.</p> + <p>See <a class="externalLink" href="http://helix.apache.org/javadocs/1.4.1/reference/org/apache/helix/store/package-summary.html";>HelixManager.getHelixPropertyStore</a> for details.</p> + </section> +</section> + </div> + </div> + </div> + </div> + + </div><!-- /container --> + + <!-- Footer + ================================================== --> + <footer class="well"> + <div class="container"> + <div class="row"> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Get Helix</li> + <li > + <a href="download.html" title="Download">Download</a> + </li> + <li > + <a href="Building.html" title="Building">Building</a> + </li> + <li > + <a href="releasenotes/release-1.4.1.html" title="Release Notes">Release Notes</a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Hands-On</li> + <li > + <a href="Quickstart.html" title="Quick Start">Quick Start</a> + </li> + <li > + <a href="Tutorial.html" title="Tutorial">Tutorial</a> + </li> + <li > + <a href="../javadocs/1.4.1" title="Javadocs">Javadocs</a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Recipes</li> + <li > + <a href="recipes/lock_manager.html" title="Distributed lock manager">Distributed lock manager</a> + </li> + <li > + <a href="recipes/rabbitmq_consumer_group.html" title="Rabbit MQ consumer group">Rabbit MQ consumer group</a> + </li> + <li > + <a href="recipes/rsync_replicated_file_store.html" title="Rsync replicated file store">Rsync replicated file store</a> + </li> + <li > + <a href="recipes/service_discovery.html" title="Service discovery">Service discovery</a> + </li> + <li > + <a href="recipes/task_dag_execution.html" title="Distributed task DAG execution">Distributed task DAG execution</a> + </li> + </ul> + </div> + </div> + </div> + </footer> + + <div class="container subfooter"> + <div class="row"> + <div class="span12"> + <p class="pull-right"><a href="#">Back to top</a></p> + <p class="copyright">Copyright ©2024 <a href="http://www.apache.org";>Apache Software Foundation</a>. 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id="bannerLeft"><img src="../images/helix-logo.jpg" alt='"''"' /></a> + <p class="lead">A cluster management framework for partitioned and replicated distributed resources</p> + </div> + <div class="pull-right"> + <a href="http://www.apache.org/"; id="bannerRight"><img src="../images/feather_small.gif" alt='"''"' /></a> + </div> + </div> + </div> + </div> + <div> + <ul class="breadcrumb"> + <li><a href="../" title="Apache Helix">Apache Helix</a></li> + <li class="divider">/</li> + <li><a href="./" title="Release 1.4.1">Release 1.4.1</a></li> + <li class="divider">/</li> + <li>Tutorial - Rebalancing Algorithms</li> + <li class="publishDate version-date pull-right">Last Published: 2024-11-18</li> + </ul> + </div> + </header> + + <div class="main-body"> + <div class="row"> + <div class="span12"> + <div class="body-content"> +<!-- +Licensed to the Apache Software Foundation (ASF) under one +or more contributor license agreements. See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you under the Apache License, Version 2.0 (the +"License"); you may not use this file except in compliance +with the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, +software distributed under the License is distributed on an +"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +KIND, either express or implied. See the License for the +specific language governing permissions and limitations +under the License. +--> +<section> + <div class="page-header"> + <h2 id="Helix_Tutorial:_Rebalancing_Algorithms"><a href="./Tutorial.html">Helix Tutorial</a>: Rebalancing Algorithms</h2> + </div> + <p>The placement of partitions in a distributed system is essential for the reliability and scalability of the system. For example, when a node fails, it is important that the partitions hosted on that node are reallocated evenly among the remaining nodes. Consistent hashing is one such algorithm that can satisfy this guarantee. Helix provides a variant of consistent hashing based on the RUSH algorithm, among others.</p> + <p>This means given a number of partitions, replicas and number of nodes, Helix does the automatic assignment of partition to nodes such that:</p> + <ul> + <li>Each node has the same number of partitions</li> + <li>Replicas of the same partition do not stay on the same node</li> + <li>When a node fails, the partitions will be equally distributed among the remaining nodes</li> + <li>When new nodes are added, the number of partitions moved will be minimized along with satisfying the above criteria</li> + </ul> + <p>Helix employs a rebalancing algorithm to compute the <i>ideal state</i> of the system. When the <i>current state</i> differs from the <i>ideal state</i>, Helix uses it as the target state of the system and computes the appropriate transitions needed to bring it to the <i>ideal state</i>.</p> + <p>Helix makes it easy to perform this operation, while giving you control over the algorithm. In this section, we'll see how to implement the desired behavior.</p> + <p>Helix has four options for rebalancing, in increasing order of customization by the system builder:</p> + <ul> + <li>FULL_AUTO</li> + <li>SEMI_AUTO</li> + <li>CUSTOMIZED</li> + <li>USER_DEFINED</li> + </ul> + <div class="source"> + <pre><code> |FULL_AUTO | SEMI_AUTO | CUSTOMIZED| USER_DEFINED | + ---------------------------------------------------------| + LOCATION | HELIX | APP | APP | APP | + ---------------------------------------------------------| + STATE | HELIX | HELIX | APP | APP | + ---------------------------------------------------------- +</code></pre> + </div> + <section> + <h3 id="FULL_AUTO">FULL_AUTO</h3> + <p>When the rebalance mode is set to FULL_AUTO, Helix controls both the location of the replica along with the state. This option is useful for applications where creation of a replica is not expensive.</p> + <p>For example, consider this system that uses a LeaderStandby state model, with 3 partitions and 2 replicas in the ideal state.</p> + <div class="source"> + <pre><code>{ + "id" : "MyResource", + "simpleFields" : { + "REBALANCE_MODE" : "FULL_AUTO", + "NUM_PARTITIONS" : "3", + "REPLICAS" : "2", + "STATE_MODEL_DEF_REF" : "LeaderStandby", + } + "listFields" : { + "MyResource_0" : [], + "MyResource_1" : [], + "MyResource_2" : [] + }, + "mapFields" : { + } +} +</code></pre> + </div> + <p>If there are 3 nodes in the cluster, then Helix will balance the leaders and standbys equally. The ideal state is therefore:</p> + <div class="source"> + <pre><code>{ + "id" : "MyResource", + "simpleFields" : { + "NUM_PARTITIONS" : "3", + "REPLICAS" : "2", + "STATE_MODEL_DEF_REF" : "LeaderStandby", + }, + "mapFields" : { + "MyResource_0" : { + "N1" : "LEADER", + "N2" : "STANDBY", + }, + "MyResource_1" : { + "N2" : "LEADER", + "N3" : "STANDBY", + }, + "MyResource_2" : { + "N3" : "LEADER", + "N1" : "STANDBY", + } + } +} +</code></pre> + </div> + <p>Another typical example is evenly distributing a group of tasks among the currently healthy processes. For example, if there are 60 tasks and 4 nodes, Helix assigns 15 tasks to each node. When one node fails, Helix redistributes its 15 tasks to the remaining 3 nodes, resulting in a balanced 20 tasks per node. Similarly, if a node is added, Helix re-allocates 3 tasks from each of the 4 nodes to the 5th node, resulting in a balanced distribution of 12 tasks per node..</p> + </section> + <section> + <h3 id="SEMI_AUTO">SEMI_AUTO</h3> + <p>When the application needs to control the placement of the replicas, use the SEMI_AUTO rebalance mode.</p> + <p>Example: In the ideal state below, the partition 'MyResource_0' is constrained to be placed only on node1 or node2. The choice of <i>state</i> is still controlled by Helix. That means MyResource_0.LEADER could be on node1 and MyResource_0.STANDBY on node2, or vice-versa but neither would be placed on node3.</p> + <div class="source"> + <pre><code>{ + "id" : "MyResource", + "simpleFields" : { + "REBALANCE_MODE" : "SEMI_AUTO", + "NUM_PARTITIONS" : "3", + "REPLICAS" : "2", + "STATE_MODEL_DEF_REF" : "LeaderStandby", + } + "listFields" : { + "MyResource_0" : [node1, node2], + "MyResource_1" : [node2, node3], + "MyResource_2" : [node3, node1] + }, + "mapFields" : { + } +} +</code></pre> + </div> + <p>The LeaderStandby state model requires that a partition has exactly one LEADER at all times, and the other replicas should be STANDBYs. In this simple example with 2 replicas per partition, there would be one LEADER and one STANDBY. Upon failover, a STANDBY has to assume leadership, and a new STANDBY will be generated.</p> + <p>In this mode when node1 fails, unlike in FULL_AUTO mode the partition is <i>not</i> moved from node1 to node3. Instead, Helix will decide to change the state of MyResource_0 on node2 from STANDBY to LEADER, based on the system constraints.</p> + </section> + <section> + <h3 id="CUSTOMIZED">CUSTOMIZED</h3> + <p>Helix offers a third mode called CUSTOMIZED, in which the application controls the placement <i>and</i> state of each replica. The application needs to implement a callback interface that Helix invokes when the cluster state changes. Within this callback, the application can recompute the idealstate. Helix will then issue appropriate transitions such that <i>Idealstate</i> and <i>Currentstate</i> converges.</p> + <p>Here's an example, again with 3 partitions, 2 replicas per partition, and the LeaderStandby state model:</p> + <div class="source"> + <pre><code>{ + "id" : "MyResource", + "simpleFields" : { + "REBALANCE_MODE" : "CUSTOMIZED", + "NUM_PARTITIONS" : "3", + "REPLICAS" : "2", + "STATE_MODEL_DEF_REF" : "LeaderStandby", + }, + "mapFields" : { + "MyResource_0" : { + "N1" : "LEADER", + "N2" : "STANDBY", + }, + "MyResource_1" : { + "N2" : "LEADER", + "N3" : "STANDBY", + }, + "MyResource_2" : { + "N3" : "LEADER", + "N1" : "STANDBY", + } + } +} +</code></pre> + </div> + <p>Suppose the current state of the system is âMyResource_0â -> {N1:LEADER, N2:STANDBY} and the application changes the ideal state to âMyResource_0â -> {N1:STANDBY,N2:LEADER}. While the application decides which node is LEADER and which is STANDBY, Helix will not blindly issue LEADER-->STANDBY to N1 and STANDBY-->LEADER to N2 in parallel, since that might result in a transient state where both N1 and N2 are leaders, which violates the LeaderStandby constraint that there is exactly one LEADER at a time. Helix will first issue LEADER-->STANDBY to N1 and after it is completed, it will issue STANDBY-->LEADER to N2.</p> + </section> + <section> + <h3 id="USER_DEFINED">USER_DEFINED</h3> + <p>For maximum flexibility, Helix exposes an interface that can allow applications to plug in custom rebalancing logic. By providing the name of a class that implements the Rebalancer interface, Helix will automatically call the contained method whenever there is a change to the live participants in the cluster. For more, see <a href="./tutorial_user_def_rebalancer.html">User-Defined Rebalancer</a>.</p> + </section> + <section> + <h3 id="Backwards_Compatibility">Backwards Compatibility</h3> + <p>In previous versions, FULL_AUTO was called AUTO_REBALANCE and SEMI_AUTO was called AUTO. Furthermore, they were presented as the IDEAL_STATE_MODE. Helix supports both IDEAL_STATE_MODE and REBALANCE_MODE, but IDEAL_STATE_MODE is now deprecated and may be phased out in future versions.</p> + </section> +</section> + </div> + </div> + </div> + </div> + + </div><!-- /container --> + + <!-- Footer + ================================================== --> + <footer class="well"> + <div class="container"> + <div class="row"> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Get Helix</li> + <li > + <a href="download.html" title="Download">Download</a> + </li> + <li > + <a href="Building.html" title="Building">Building</a> + </li> + <li > + <a href="releasenotes/release-1.4.1.html" title="Release Notes">Release Notes</a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Hands-On</li> + <li > + <a href="Quickstart.html" title="Quick Start">Quick Start</a> + </li> + <li > + <a href="Tutorial.html" title="Tutorial">Tutorial</a> + </li> + <li > + <a href="../javadocs/1.4.1" title="Javadocs">Javadocs</a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Recipes</li> + <li > + <a href="recipes/lock_manager.html" title="Distributed lock manager">Distributed lock manager</a> + </li> + <li > + <a href="recipes/rabbitmq_consumer_group.html" title="Rabbit MQ consumer group">Rabbit MQ consumer group</a> + </li> + <li > + <a href="recipes/rsync_replicated_file_store.html" title="Rsync replicated file store">Rsync replicated file store</a> + </li> + <li > + <a href="recipes/service_discovery.html" title="Service discovery">Service discovery</a> + </li> + <li > + <a href="recipes/task_dag_execution.html" title="Distributed task DAG execution">Distributed task DAG execution</a> + </li> + </ul> + </div> + </div> + </div> + </footer> + + <div class="container subfooter"> + <div class="row"> + <div class="span12"> + <p class="pull-right"><a href="#">Back to top</a></p> + <p class="copyright">Copyright ©2024 <a href="http://www.apache.org";>Apache Software Foundation</a>. 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