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Posted to commits@helix.apache.org by ka...@apache.org on 2014/01/02 01:14:10 UTC
[10/31] Rearrange website directory structure
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/recipes/user_def_rebalancer.md
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+<!---
+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.
+-->
+
+Lock Manager with a User-Defined Rebalancer
+-------------------------------------------
+Helix is able to compute node preferences and state assignments automatically using general-purpose algorithms. In many cases, a distributed system implementer may choose to instead define a customized approach to computing the location of replicas, the state mapping, or both in response to the addition or removal of participants. The following is an implementation of the [Distributed Lock Manager](./lock_manager.html) that includes a user-defined rebalancer.
+
+### Define the Cluster and Resource
+
+The YAML file below fully defines the cluster and the locks. A lock can be in one of two states: locked and unlocked. Transitions can happen in either direction, and the locked is preferred. A resource in this example is the entire collection of locks to distribute. A partition is mapped to a lock; in this case that means there are 12 locks. These 12 locks will be distributed across 3 nodes. The constraints indicate that only one replica of a lock can be in the locked state at any given time. These locks can each only have a single holder, defined by a replica count of 1.
+
+Notice the rebalancer section of the definition. The mode is set to USER_DEFINED and the class name refers to the plugged-in rebalancer implementation that inherits from [HelixRebalancer](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/controller/rebalancer/HelixRebalancer.html). This implementation is called whenever the state of the cluster changes, as is the case when participants are added or removed from the system.
+
+Location: `incubator-helix/recipes/user-defined-rebalancer/src/main/resources/lock-manager-config.yaml`
+
+```
+clusterName: lock-manager-custom-rebalancer # unique name for the cluster
+resources:
+ - name: lock-group # unique resource name
+ rebalancer: # we will provide our own rebalancer
+ mode: USER_DEFINED
+ class: org.apache.helix.userdefinedrebalancer.LockManagerRebalancer
+ partitions:
+ count: 12 # number of locks
+ replicas: 1 # number of simultaneous holders for each lock
+ stateModel:
+ name: lock-unlock # unique model name
+ states: [LOCKED, RELEASED, DROPPED] # the list of possible states
+ transitions: # the list of possible transitions
+ - name: Unlock
+ from: LOCKED
+ to: RELEASED
+ - name: Lock
+ from: RELEASED
+ to: LOCKED
+ - name: DropLock
+ from: LOCKED
+ to: DROPPED
+ - name: DropUnlock
+ from: RELEASED
+ to: DROPPED
+ - name: Undrop
+ from: DROPPED
+ to: RELEASED
+ initialState: RELEASED
+ constraints:
+ state:
+ counts: # maximum number of replicas of a partition that can be in each state
+ - name: LOCKED
+ count: "1"
+ - name: RELEASED
+ count: "-1"
+ - name: DROPPED
+ count: "-1"
+ priorityList: [LOCKED, RELEASED, DROPPED] # states in order of priority
+ transition: # transitions priority to enforce order that transitions occur
+ priorityList: [Unlock, Lock, Undrop, DropUnlock, DropLock]
+participants: # list of nodes that can acquire locks
+ - name: localhost_12001
+ host: localhost
+ port: 12001
+ - name: localhost_12002
+ host: localhost
+ port: 12002
+ - name: localhost_12003
+ host: localhost
+ port: 12003
+```
+
+Then, Helix\'s YAMLClusterSetup tool can read in the configuration and bootstrap the cluster immediately:
+
+```
+YAMLClusterSetup setup = new YAMLClusterSetup(zkAddress);
+InputStream input =
+ Thread.currentThread().getContextClassLoader()
+ .getResourceAsStream("lock-manager-config.yaml");
+YAMLClusterSetup.YAMLClusterConfig config = setup.setupCluster(input);
+```
+
+### Write a Rebalancer
+Below is a full implementation of a rebalancer that extends [HelixRebalancer](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/controller/rebalancer/HelixRebalancer.html). In this case, it simply throws out the previous resource assignment, computes the target node for as many partition replicas as can hold a lock in the LOCKED state (in this example, one), and assigns them the LOCKED state (which is at the head of the state preference list). Clearly a more robust implementation would likely examine the current ideal state to maintain current assignments, and the full state list to handle models more complicated than this one. However, for a simple lock holder implementation, this is sufficient.
+
+Location: `incubator-helix/recipes/user-rebalanced-lock-manager/src/main/java/org/apache/helix/userdefinedrebalancer/LockManagerRebalancer.java`
+
+```
+@Override
+public void init(HelixManager manager, ControllerContextProvider contextProvider) {
+ // do nothing; this rebalancer is independent of the manager
+}
+
+@Override
+public ResourceAssignment computeResourceMapping(RebalancerConfig rebalancerConfig,
+ ResourceAssignment prevAssignment, Cluster cluster, ResourceCurrentState currentState) {
+ // get a typed config
+ PartitionedRebalancerConfig config = PartitionedRebalancerConfig.from(rebalancerConfig);
+
+ // Initialize an empty mapping of locks to participants
+ ResourceAssignment assignment = new ResourceAssignment(config.getResourceId());
+
+ // Get the list of live participants in the cluster
+ List<ParticipantId> liveParticipants =
+ new ArrayList<ParticipantId>(cluster.getLiveParticipantMap().keySet());
+
+ // Get the state model (should be a simple lock/unlock model) and the highest-priority state
+ StateModelDefId stateModelDefId = config.getStateModelDefId();
+ StateModelDefinition stateModelDef = cluster.getStateModelMap().get(stateModelDefId);
+ if (stateModelDef.getStatesPriorityList().size() < 1) {
+ LOG.error("Invalid state model definition. There should be at least one state.");
+ return assignment;
+ }
+ State lockState = stateModelDef.getTypedStatesPriorityList().get(0);
+
+ // Count the number of participants allowed to lock each lock
+ String stateCount = stateModelDef.getNumParticipantsPerState(lockState);
+ int lockHolders = 0;
+ try {
+ // a numeric value is a custom-specified number of participants allowed to lock the lock
+ lockHolders = Integer.parseInt(stateCount);
+ } catch (NumberFormatException e) {
+ LOG.error("Invalid state model definition. The lock state does not have a valid count");
+ return assignment;
+ }
+
+ // 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.
+ // This assumes a simple lock-unlock model where the only state of interest is which nodes have
+ // acquired each lock.
+ int i = 0;
+ for (PartitionId partition : config.getPartitionSet()) {
+ Map<ParticipantId, State> replicaMap = new HashMap<ParticipantId, State>();
+ for (int j = i; j < i + lockHolders; j++) {
+ int participantIndex = j % liveParticipants.size();
+ ParticipantId participant = liveParticipants.get(participantIndex);
+ // enforce that a participant can only have one instance of a given lock
+ if (!replicaMap.containsKey(participant)) {
+ replicaMap.put(participant, lockState);
+ }
+ }
+ assignment.addReplicaMap(partition, replicaMap);
+ i++;
+ }
+ return assignment;
+}
+```
+
+### Start up the Participants
+Here is a lock class based on the newly defined lock-unlock state model so that the participant can receive callbacks on state transitions.
+
+Location: `incubator-helix/recipes/user-rebalanced-lock-manager/src/main/java/org/apache/helix/userdefinedrebalancer/Lock.java`
+
+```
+public class Lock extends StateModel {
+ private String lockName;
+
+ public Lock(String lockName) {
+ this.lockName = lockName;
+ }
+
+ @Transition(from = "RELEASED", to = "LOCKED")
+ public void lock(Message m, NotificationContext context) {
+ System.out.println(context.getManager().getInstanceName() + " acquired lock:" + lockName);
+ }
+
+ @Transition(from = "LOCKED", to = "RELEASED")
+ public void release(Message m, NotificationContext context) {
+ System.out.println(context.getManager().getInstanceName() + " releasing lock:" + lockName);
+ }
+}
+```
+
+Here is the factory to make the Lock class accessible.
+
+Location: `incubator-helix/recipes/user-rebalanced-lock-manager/src/main/java/org/apache/helix/userdefinedrebalancer/LockFactory.java`
+
+```
+public class LockFactory extends StateModelFactory<Lock> {
+ @Override
+ public Lock createNewStateModel(String lockName) {
+ return new Lock(lockName);
+ }
+}
+```
+
+Finally, here is the factory registration and the start of the participant:
+
+```
+participantManager =
+ HelixManagerFactory.getZKHelixManager(clusterName, participantName, InstanceType.PARTICIPANT,
+ zkAddress);
+participantManager.getStateMachineEngine().registerStateModelFactory(stateModelName,
+ new LockFactory());
+participantManager.connect();
+```
+
+### Start up the Controller
+
+```
+controllerManager =
+ HelixControllerMain.startHelixController(zkAddress, config.clusterName, "controller",
+ HelixControllerMain.STANDALONE);
+```
+
+### Try It Out
+
+```
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+mvn clean install package -DskipTests
+cd recipes/user-defined-rebalancer/target/user-defined-rebalancer-pkg/bin
+chmod +x *
+./lock-manager-demo.sh
+```
+
+#### Output
+
+```
+./lock-manager-demo
+STARTING localhost_12002
+STARTING localhost_12001
+STARTING localhost_12003
+STARTED localhost_12001
+STARTED localhost_12003
+STARTED localhost_12002
+localhost_12003 acquired lock:lock-group_4
+localhost_12002 acquired lock:lock-group_8
+localhost_12001 acquired lock:lock-group_10
+localhost_12001 acquired lock:lock-group_3
+localhost_12001 acquired lock:lock-group_6
+localhost_12003 acquired lock:lock-group_0
+localhost_12002 acquired lock:lock-group_5
+localhost_12001 acquired lock:lock-group_9
+localhost_12002 acquired lock:lock-group_2
+localhost_12003 acquired lock:lock-group_7
+localhost_12003 acquired lock:lock-group_11
+localhost_12002 acquired lock:lock-group_1
+lockName acquired By
+======================================
+lock-group_0 localhost_12003
+lock-group_1 localhost_12002
+lock-group_10 localhost_12001
+lock-group_11 localhost_12003
+lock-group_2 localhost_12002
+lock-group_3 localhost_12001
+lock-group_4 localhost_12003
+lock-group_5 localhost_12002
+lock-group_6 localhost_12001
+lock-group_7 localhost_12003
+lock-group_8 localhost_12002
+lock-group_9 localhost_12001
+Stopping the first participant
+localhost_12001 Interrupted
+localhost_12002 acquired lock:lock-group_3
+localhost_12003 acquired lock:lock-group_6
+localhost_12003 acquired lock:lock-group_10
+localhost_12002 acquired lock:lock-group_9
+lockName acquired By
+======================================
+lock-group_0 localhost_12003
+lock-group_1 localhost_12002
+lock-group_10 localhost_12003
+lock-group_11 localhost_12003
+lock-group_2 localhost_12002
+lock-group_3 localhost_12002
+lock-group_4 localhost_12003
+lock-group_5 localhost_12002
+lock-group_6 localhost_12003
+lock-group_7 localhost_12003
+lock-group_8 localhost_12002
+lock-group_9 localhost_12002
+```
+
+Notice that the lock assignment directly follows the assignment generated by the user-defined rebalancer both initially and after a participant is removed from the system.
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_accessors.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Logical Accessors</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Logical Accessors
+
+Helix constructs follow a logical hierarchy. A cluster contains participants, and serve logical resources. Each resource can be divided into partitions, which themselves can be replicated. Helix now supports configuring and modifying clusters programmatically in a hierarchical way using logical accessors.
+
+[Click here](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/api/accessor/package-summary.html) for the Javadocs of the accessors.
+
+### An Example
+
+#### Configure a Participant
+
+A participant is a combination of a host, port, and a UserConfig. A UserConfig is an arbitrary set of properties a Helix user can attach to any participant.
+
+```
+ParticipantId participantId = ParticipantId.from("localhost_12345");
+ParticipantConfig participantConfig = new ParticipantConfig.Builder(participantId)
+ .hostName("localhost").port(12345).build();
+```
+
+#### Configure a Resource
+
+##### RebalancerConfig
+A Resource is essentially a combination of a RebalancerConfig and a UserConfig. A [RebalancerConfig](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/controller/rebalancer/config/RebalancerConfig.html) consists of all the key properties required to rebalance a resource, including how it is partitioned and replicated, and what state model it follows. Most Helix resources will make use of a [PartitionedRebalancerConfig](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/controller/rebalancer/config/PartitionedRebalancerConfig.html), which is a RebalancerConfig for resources that are partitioned.
+
+Recall that there are four [rebalancing modes](./tutorial_rebalance.html) that Helix provides, and so Helix also provides the following subclasses for PartitionedRebalancerConfig:
+
+* [FullAutoRebalancerConfig](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/controller/rebalancer/config/FullAutoRebalancerConfig.html) for FULL_AUTO mode.
+* [SemiAutoRebalancerConfig](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/controller/rebalancer/config/SemiAutoRebalancerConfig.html) for SEMI_AUTO mode. This class allows a user to specify "preference lists" to indicate where each partition should ideally be served
+* [CustomRebalancerConfig](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/controller/rebalancer/config/CustomRebalancerConfig.html) for CUSTOMIZED mode. This class allows a user tp specify "preference maps" to indicate the location and state for each partition replica.
+
+Helix also supports arbitrary subclasses of PartitionedRebalancerConfig and even arbitrary implementations of RebalancerConfig for applications that need a user-defined approach for rebalancing. For more, see [User-Defined Rebalancing](./tutorial_user_def_rebalancer.html)
+
+##### In Action
+
+Here is an example of a configured resource with a rebalancer config for FULL_AUTO mode and two partitions:
+
+```
+ResourceId resourceId = ResourceId.from("sampleResource");
+StateModelDefinition stateModelDef = getStateModelDef();
+Partition partition1 = new Partition(PartitionId.from(resourceId, "1"));
+Partition partition2 = new Partition(PartitionId.from(resourceId, "2"));
+FullAutoRebalancerConfig rebalanceConfig =
+ new FullAutoRebalancerConfig.Builder(resourceId).replicaCount(1).addPartition(partition1)
+ .addPartition(partition2).stateModelDefId(stateModelDef.getStateModelDefId()).build();
+ResourceConfig resourceConfig =
+ new ResourceConfig.Builder(resourceId).rebalancerConfig(rebalanceConfig).build();
+```
+
+#### Add the Cluster
+
+Now we can take the participant and resource configured above, add them to a cluster configuration, and then persist the entire cluster at once using a ClusterAccessor:
+
+```
+// configure the cluster
+ClusterId clusterId = ClusterId.from("sampleCluster");
+ClusterConfig clusterConfig = new ClusterConfig.Builder(clusterId).addParticipant(participantConfig)
+ .addResource(resourceConfig).addStateModelDefinition(stateModelDef).build();
+
+// create the cluster using a ClusterAccessor
+HelixConnection connection = new ZkHelixConnection(zkAddr);
+connection.connect();
+ClusterAccessor clusterAccessor = connection.createClusterAccessor(clusterId);
+clusterAccessor.createCluster(clusterConfig);
+```
+
+### Create, Read, Update, and Delete
+
+Note that you don't have to specify the entire cluster beforehand! Helix provides a ClusterAccessor, ParticipantAccessor, and ResourceAccessor to allow changing as much or as little of the cluster as needed on the fly. You can add a resource or participant to a cluster, reconfigure a resource, participant, or cluster, remove components from the cluster, and more. See the [Javadocs](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/api/accessor/package-summary.html) to see all that the accessor classes can do.
+
+#### Delta Classes
+
+Updating a cluster, participant, or resource should involve selecting the element to change, and then letting Helix change only that component. To do this, Helix has included Delta classes for ClusterConfig, ParticipantConfig, and ResourceConfig.
+
+#### Example: Updating a Participant
+
+Tags are used for Helix depolyments where only certain participants can be allowed to serve certain resources. To do this, Helix only assigns resource replicas to participants who have a tag that the resource specifies. In this example, we will use ParticipantConfig.Delta to remove a participant tag and add another as part of a reconfiguration.
+
+```
+// specify the change to the participant
+ParticipantConfig.Delta delta = new ParticipantConfig.Delta(participantId).addTag("newTag").removeTag("oldTag");
+
+// update the participant configuration
+ParticipantAccessor participantAccessor = connection.createParticipantAccessor(clusterId);
+participantAccessor.updateParticipant(participantId, delta);
+```
+
+#### Example: Dropping a Resource
+Removing a resource from the cluster is quite simple:
+
+```
+clusterAccessor.dropResourceFromCluster(resourceId);
+```
+
+#### Example: Reading the Cluster
+Reading a full snapshot of the cluster is also a one-liner:
+
+```
+Cluster cluster = clusterAccessor.readCluster();
+```
+
+### Atomic Accessors
+
+Helix also includes versions of ClusterAccessor, ParticipantAccessor, and ResourceAccessor that can complete operations atomically relative to one another. The specific semantics of the atomic operations are included in the Javadocs. These atomic classes should be used sparingly and only in cases where contention can adversely affect the correctness of a Helix-based cluster. For most deployments, this is not the case, and using these classes will cause a degradation in performance. However, the interface for all atomic accessors mirrors that of the non-atomic accessors.
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_admin.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Admin Operations</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Admin Operations
+
+Helix provides a set of admin APIs for cluster management operations. They are supported via:
+
+* Java API
+* Command Line Interface
+* REST Interface via helix-admin-webapp
+
+### Java API
+See interface [_org.apache.helix.HelixAdmin_](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/HelixAdmin.html)
+
+### Command Line Interface
+The command line tool comes with helix-core package:
+
+Get the command line tool:
+
+```
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+./build
+cd helix-core/target/helix-core-pkg/bin
+chmod +x *.sh
+```
+
+Get help:
+
+```
+./helix-admin.sh --help
+```
+
+All other commands have this form:
+
+```
+./helix-admin.sh --zkSvr <ZookeeperServerAddress> <command> <parameters>
+```
+
+#### Supported Commands
+
+| Command Syntax | Description |
+| -------------- | ----------- |
+| _\-\-activateCluster \<clusterName controllerCluster true/false\>_ | Enable/disable a cluster in distributed controller mode |
+| _\-\-addCluster \<clusterName\>_ | Add a new cluster |
+| _\-\-addIdealState \<clusterName resourceName fileName.json\>_ | Add an ideal state to a cluster |
+| _\-\-addInstanceTag \<clusterName instanceName tag\>_ | Add a tag to an instance |
+| _\-\-addNode \<clusterName instanceId\>_ | Add an instance to a cluster |
+| _\-\-addResource \<clusterName resourceName partitionNumber stateModelName\>_ | Add a new resource to a cluster |
+| _\-\-addResourceProperty \<clusterName resourceName propertyName propertyValue\>_ | Add a resource property |
+| _\-\-addStateModelDef \<clusterName fileName.json\>_ | Add a State model definition to a cluster |
+| _\-\-dropCluster \<clusterName\>_ | Delete a cluster |
+| _\-\-dropNode \<clusterName instanceId\>_ | Remove a node from a cluster |
+| _\-\-dropResource \<clusterName resourceName\>_ | Remove an existing resource from a cluster |
+| _\-\-enableCluster \<clusterName true/false\>_ | Enable/disable a cluster |
+| _\-\-enableInstance \<clusterName instanceId true/false\>_ | Enable/disable an instance |
+| _\-\-enablePartition \<true/false clusterName nodeId resourceName partitionName\>_ | Enable/disable a partition |
+| _\-\-getConfig \<configScope configScopeArgs configKeys\>_ | Get user configs |
+| _\-\-getConstraints \<clusterName constraintType\>_ | Get constraints |
+| _\-\-help_ | print help information |
+| _\-\-instanceGroupTag \<instanceTag\>_ | Specify instance group tag, used with rebalance command |
+| _\-\-listClusterInfo \<clusterName\>_ | Show information of a cluster |
+| _\-\-listClusters_ | List all clusters |
+| _\-\-listInstanceInfo \<clusterName instanceId\>_ | Show information of an instance |
+| _\-\-listInstances \<clusterName\>_ | List all instances in a cluster |
+| _\-\-listPartitionInfo \<clusterName resourceName partitionName\>_ | Show information of a partition |
+| _\-\-listResourceInfo \<clusterName resourceName\>_ | Show information of a resource |
+| _\-\-listResources \<clusterName\>_ | List all resources in a cluster |
+| _\-\-listStateModel \<clusterName stateModelName\>_ | Show information of a state model |
+| _\-\-listStateModels \<clusterName\>_ | List all state models in a cluster |
+| _\-\-maxPartitionsPerNode \<maxPartitionsPerNode\>_ | Specify the max partitions per instance, used with addResourceGroup command |
+| _\-\-rebalance \<clusterName resourceName replicas\>_ | Rebalance a resource |
+| _\-\-removeConfig \<configScope configScopeArgs configKeys\>_ | Remove user configs |
+| _\-\-removeConstraint \<clusterName constraintType constraintId\>_ | Remove a constraint |
+| _\-\-removeInstanceTag \<clusterName instanceId tag\>_ | Remove a tag from an instance |
+| _\-\-removeResourceProperty \<clusterName resourceName propertyName\>_ | Remove a resource property |
+| _\-\-resetInstance \<clusterName instanceId\>_ | Reset all erroneous partitions on an instance |
+| _\-\-resetPartition \<clusterName instanceId resourceName partitionName\>_ | Reset an erroneous partition |
+| _\-\-resetResource \<clusterName resourceName\>_ | Reset all erroneous partitions of a resource |
+| _\-\-setConfig \<configScope configScopeArgs configKeyValueMap\>_ | Set user configs |
+| _\-\-setConstraint \<clusterName constraintType constraintId constraintKeyValueMap\>_ | Set a constraint |
+| _\-\-swapInstance \<clusterName oldInstance newInstance\>_ | Swap an old instance with a new instance |
+| _\-\-zkSvr \<ZookeeperServerAddress\>_ | Provide zookeeper address |
+
+### REST Interface
+
+The REST interface comes wit helix-admin-webapp package:
+
+```
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+./build
+cd helix-admin-webapp/target/helix-admin-webapp-pkg/bin
+chmod +x *.sh
+./run-rest-admin.sh --zkSvr <zookeeperAddress> --port <port> // make sure ZooKeeper is running
+```
+
+#### URL and support methods
+
+* _/clusters_
+ * List all clusters
+
+ ```
+ curl http://localhost:8100/clusters
+ ```
+
+ * Add a cluster
+
+ ```
+ curl -d 'jsonParameters={"command":"addCluster","clusterName":"MyCluster"}' -H "Content-Type: application/json" http://localhost:8100/clusters
+ ```
+
+* _/clusters/{clusterName}_
+ * List cluster information
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster
+ ```
+
+ * Enable/disable a cluster in distributed controller mode
+
+ ```
+ curl -d 'jsonParameters={"command":"activateCluster","grandCluster":"MyControllerCluster","enabled":"true"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster
+ ```
+
+ * Remove a cluster
+
+ ```
+ curl -X DELETE http://localhost:8100/clusters/MyCluster
+ ```
+
+* _/clusters/{clusterName}/resourceGroups_
+ * List all resources in a cluster
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/resourceGroups
+ ```
+
+ * Add a resource to cluster
+
+ ```
+ curl -d 'jsonParameters={"command":"addResource","resourceGroupName":"MyDB","partitions":"8","stateModelDefRef":"MasterSlave" }' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/resourceGroups
+ ```
+
+* _/clusters/{clusterName}/resourceGroups/{resourceName}_
+ * List resource information
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/resourceGroups/MyDB
+ ```
+
+ * Drop a resource
+
+ ```
+ curl -X DELETE http://localhost:8100/clusters/MyCluster/resourceGroups/MyDB
+ ```
+
+ * Reset all erroneous partitions of a resource
+
+ ```
+ curl -d 'jsonParameters={"command":"resetResource"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/resourceGroups/MyDB
+ ```
+
+* _/clusters/{clusterName}/resourceGroups/{resourceName}/idealState_
+ * Rebalance a resource
+
+ ```
+ curl -d 'jsonParameters={"command":"rebalance","replicas":"3"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/resourceGroups/MyDB/idealState
+ ```
+
+ * Add an ideal state
+
+ ```
+ echo jsonParameters={
+ "command":"addIdealState"
+ }&newIdealState={
+ "id" : "MyDB",
+ "simpleFields" : {
+ "IDEAL_STATE_MODE" : "AUTO",
+ "NUM_PARTITIONS" : "8",
+ "REBALANCE_MODE" : "SEMI_AUTO",
+ "REPLICAS" : "0",
+ "STATE_MODEL_DEF_REF" : "MasterSlave",
+ "STATE_MODEL_FACTORY_NAME" : "DEFAULT"
+ },
+ "listFields" : {
+ },
+ "mapFields" : {
+ "MyDB_0" : {
+ "localhost_1001" : "MASTER",
+ "localhost_1002" : "SLAVE"
+ }
+ }
+ }
+ > newIdealState.json
+ curl -d @'./newIdealState.json' -H 'Content-Type: application/json' http://localhost:8100/clusters/MyCluster/resourceGroups/MyDB/idealState
+ ```
+
+ * Add resource property
+
+ ```
+ curl -d 'jsonParameters={"command":"addResourceProperty","REBALANCE_TIMER_PERIOD":"500"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/resourceGroups/MyDB/idealState
+ ```
+
+* _/clusters/{clusterName}/resourceGroups/{resourceName}/externalView_
+ * Show resource external view
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/resourceGroups/MyDB/externalView
+ ```
+* _/clusters/{clusterName}/instances_
+ * List all instances
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/instances
+ ```
+
+ * Add an instance
+
+ ```
+ curl -d 'jsonParameters={"command":"addInstance","instanceNames":"localhost_1001"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/instances
+ ```
+
+ * Swap an instance
+
+ ```
+ curl -d 'jsonParameters={"command":"swapInstance","oldInstance":"localhost_1001", "newInstance":"localhost_1002"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/instances
+ ```
+* _/clusters/{clusterName}/instances/{instanceName}_
+ * Show instance information
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/instances/localhost_1001
+ ```
+
+ * Enable/disable an instance
+
+ ```
+ curl -d 'jsonParameters={"command":"enableInstance","enabled":"false"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/instances/localhost_1001
+ ```
+
+ * Drop an instance
+
+ ```
+ curl -X DELETE http://localhost:8100/clusters/MyCluster/instances/localhost_1001
+ ```
+
+ * Disable/enable partitions on an instance
+
+ ```
+ curl -d 'jsonParameters={"command":"enablePartition","resource": "MyDB","partition":"MyDB_0", "enabled" : "false"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/instances/localhost_1001
+ ```
+
+ * Reset an erroneous partition on an instance
+
+ ```
+ curl -d 'jsonParameters={"command":"resetPartition","resource": "MyDB","partition":"MyDB_0"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/instances/localhost_1001
+ ```
+
+ * Reset all erroneous partitions on an instance
+
+ ```
+ curl -d 'jsonParameters={"command":"resetInstance"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/instances/localhost_1001
+ ```
+
+* _/clusters/{clusterName}/configs_
+ * Get user cluster level config
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/configs/cluster
+ ```
+
+ * Set user cluster level config
+
+ ```
+ curl -d 'jsonParameters={"command":"setConfig","configs":"key1=value1,key2=value2"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/configs/cluster
+ ```
+
+ * Remove user cluster level config
+
+ ```
+ curl -d 'jsonParameters={"command":"removeConfig","configs":"key1,key2"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/configs/cluster
+ ```
+
+ * Get/set/remove user participant level config
+
+ ```
+ curl -d 'jsonParameters={"command":"setConfig","configs":"key1=value1,key2=value2"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/configs/participant/localhost_1001
+ ```
+
+ * Get/set/remove resource level config
+
+ ```
+ curl -d 'jsonParameters={"command":"setConfig","configs":"key1=value1,key2=value2"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/configs/resource/MyDB
+ ```
+
+* _/clusters/{clusterName}/controller_
+ * Show controller information
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/Controller
+ ```
+
+ * Enable/disable cluster
+
+ ```
+ curl -d 'jsonParameters={"command":"enableCluster","enabled":"false"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/Controller
+ ```
+
+* _/zkPath/{path}_
+ * Get information for zookeeper path
+
+ ```
+ curl http://localhost:8100/zkPath/MyCluster
+ ```
+
+* _/clusters/{clusterName}/StateModelDefs_
+ * Show all state model definitions
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/StateModelDefs
+ ```
+
+ * Add a state mdoel definition
+
+ ```
+ echo jsonParameters={
+ "command":"addStateModelDef"
+ }&newStateModelDef={
+ "id" : "OnlineOffline",
+ "simpleFields" : {
+ "INITIAL_STATE" : "OFFLINE"
+ },
+ "listFields" : {
+ "STATE_PRIORITY_LIST" : [ "ONLINE", "OFFLINE", "DROPPED" ],
+ "STATE_TRANSITION_PRIORITYLIST" : [ "OFFLINE-ONLINE", "ONLINE-OFFLINE", "OFFLINE-DROPPED" ]
+ },
+ "mapFields" : {
+ "DROPPED.meta" : {
+ "count" : "-1"
+ },
+ "OFFLINE.meta" : {
+ "count" : "-1"
+ },
+ "OFFLINE.next" : {
+ "DROPPED" : "DROPPED",
+ "ONLINE" : "ONLINE"
+ },
+ "ONLINE.meta" : {
+ "count" : "R"
+ },
+ "ONLINE.next" : {
+ "DROPPED" : "OFFLINE",
+ "OFFLINE" : "OFFLINE"
+ }
+ }
+ }
+ > newStateModelDef.json
+ curl -d @'./untitled.txt' -H 'Content-Type: application/json' http://localhost:8100/clusters/MyCluster/StateModelDefs
+ ```
+
+* _/clusters/{clusterName}/StateModelDefs/{stateModelDefName}_
+ * Show a state model definition
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/StateModelDefs/OnlineOffline
+ ```
+
+* _/clusters/{clusterName}/constraints/{constraintType}_
+ * Show all contraints
+
+ ```
+ curl http://localhost:8100/clusters/MyCluster/constraints/MESSAGE_CONSTRAINT
+ ```
+
+ * Set a contraint
+
+ ```
+ curl -d 'jsonParameters={"constraintAttributes":"RESOURCE=MyDB,CONSTRAINT_VALUE=1"}' -H "Content-Type: application/json" http://localhost:8100/clusters/MyCluster/constraints/MESSAGE_CONSTRAINT/MyConstraint
+ ```
+
+ * Remove a constraint
+
+ ```
+ curl -X DELETE http://localhost:8100/clusters/MyCluster/constraints/MESSAGE_CONSTRAINT/MyConstraint
+ ```
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_controller.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Controller</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Controller
+
+Next, let\'s implement the controller. This is the brain of the cluster. Helix makes sure there is exactly one active controller running the cluster.
+
+### Start the Helix Controller
+
+It requires the following parameters:
+
+* clusterId: A logical ID to represent the group of nodes
+* controllerId: A logical ID of the process creating the controller instance. Generally this is host:port.
+* zkConnectString: Connection string to Zookeeper. This is of the form host1:port1,host2:port2,host3:port3.
+
+```
+HelixConnection connection = new ZKHelixConnection(zkConnectString);
+HelixController controller = connection.createController(clusterId, controllerId);
+```
+
+### Controller Code
+
+The Controller needs to know about all changes in the cluster. Helix takes care of this with the default implementation.
+If you need additional functionality, see GenericHelixController and ZKHelixController for how to configure the pipeline.
+
+```
+HelixConnection connection = new ZKHelixConnection(zkConnectString);
+HelixController controller = connection.createController(clusterId, controllerId);
+controller.startAsync();
+```
+The snippet above shows how the controller is started. You can also start the controller using command line interface.
+
+```
+cd helix/helix-core/target/helix-core-pkg/bin
+./run-helix-controller.sh --zkSvr <Zookeeper ServerAddress (Required)> --cluster <Cluster name (Required)>
+```
+
+### Controller Deployment Modes
+
+Helix provides multiple options to deploy the controller.
+
+#### STANDALONE
+
+The Controller can be started as a separate process to manage a cluster. This is the recommended approach. However, since one controller can be a single point of failure, multiple controller processes are required for reliability. Even if multiple controllers are running, only one will be actively managing the cluster at any time and is decided by a leader-election process. If the leader fails, another leader will take over managing the cluster.
+
+Even though we recommend this method of deployment, it has the drawback of having to manage an additional service for each cluster. See Controller As a Service option.
+
+#### EMBEDDED
+
+If setting up a separate controller process is not viable, then it is possible to embed the controller as a library in each of the participants.
+
+#### CONTROLLER AS A SERVICE
+
+One of the cool features we added in Helix is to use a set of controllers to manage a large number of clusters.
+
+For example if you have X clusters to be managed, instead of deploying X*3 (3 controllers for fault tolerance) controllers for each cluster, one can deploy just 3 controllers. Each controller can manage X/3 clusters. If any controller fails, the remaining two will manage X/2 clusters.
+
+
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_health.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Customizing Heath Checks</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Customizing Health Checks
+
+In this chapter, we\'ll learn how to customize health checks based on metrics of your distributed system.
+
+### Health Checks
+
+Note: _this in currently in development mode, not yet ready for production._
+
+Helix provides the ability for each node in the system to report health metrics on a periodic basis.
+
+Helix supports multiple ways to aggregate these metrics:
+
+* SUM
+* AVG
+* EXPONENTIAL DECAY
+* WINDOW
+
+Helix persists the aggregated value only.
+
+Applications can define a threshold on the aggregate values according to the SLAs, and when the SLA is violated Helix will fire an alert.
+Currently Helix only fires an alert, but in a future release we plan to use these metrics to either mark the node dead or load balance the partitions.
+This feature will be valuable for distributed systems that support multi-tenancy and have a large variation in work load patterns. In addition, this can be used to detect skewed partitions (hotspots) and rebalance the cluster.
+
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_messaging.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Messaging</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Messaging
+
+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.
+
+### Example: Bootstrapping a Replica
+
+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.
+
+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.
+
+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
+
+```
+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);
+```
+
+See HelixManager.DefaultMessagingService in the [Javadocs](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/messaging/DefaultMessagingService.html) for more information.
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_participant.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Participant</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Participant
+
+In this chapter, we\'ll learn how to implement a __Participant__, which is a primary functional component of a distributed system.
+
+
+### Start the Helix Participant
+
+The Helix participant class is a common component that connects each participant with the controller.
+
+It requires the following parameters:
+
+* clusterId: A logical ID to represent the group of nodes
+* participantId: A logical ID of the process creating the manager instance. Generally this is host:port.
+* zkConnectString: Connection string to Zookeeper. This is of the form host1:port1,host2:port2,host3:port3.
+
+After the Helix participant instance is created, 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:
+
+* MasterSlaveStateModelFactory
+* LeaderStandbyStateModelFactory
+* BootstrapHandler
+* _An application-defined state model factory_
+
+
+```
+HelixConnection connection = new ZKHelixConnection(zkConnectString);
+HelixParticipant participant = connection.createParticipant(clusterId, participantId);
+StateMachineEngine stateMach = participant.getStateMachineEngine();
+
+// create a stateModelFactory that returns a statemodel object for each partition.
+HelixStateModelFactory<OnlineOfflineStateModel> stateModelFactory = new OnlineOfflineStateModelFactory();
+stateMach.registerStateModelFactory(stateModelType, stateModelFactory);
+participant.startAsync();
+```
+
+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.
+
+```
+public class OnlineOfflineStateModelFactory extends HelixStateModelFactory<OnlineOfflineStateModel> {
+ @Override
+ public OnlineOfflineStateModel createNewStateModel(PartitionId partitionId) {
+ 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 //
+ ////////////////////////////////////////////////////////////////////////////////////////////////
+ }
+}
+```
+
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_propstore.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Application Property Store</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Application Property Store
+
+In this chapter, we\'ll learn how to use the application property store.
+
+### Property Store
+
+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.
+
+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.
+
+See [HelixManager.getHelixPropertyStore](http://helix.incubator.apache.org/apidocs/reference/org/apache/helix/store/package-summary.html) for details.
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_rebalance.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Rebalancing Algorithms</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Rebalancing Algorithms
+
+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.
+
+This means given a number of partitions, replicas and number of nodes, Helix does the automatic assignment of partition to nodes such that:
+
+* Each node has the same number of partitions
+* Replicas of the same partition do not stay on the same node
+* When a node fails, the partitions will be equally distributed among the remaining nodes
+* When new nodes are added, the number of partitions moved will be minimized along with satisfying the above criteria
+
+Helix employs a rebalancing algorithm to compute the _ideal state_ of the system. When the _current state_ differs from the _ideal state_, Helix uses it as the target state of the system and computes the appropriate transitions needed to bring it to the _ideal state_.
+
+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.
+
+Helix has four options for rebalancing, in increasing order of customization by the system builder:
+
+* FULL_AUTO
+* SEMI_AUTO
+* CUSTOMIZED
+* USER_DEFINED
+
+```
+ |FULL_AUTO | SEMI_AUTO | CUSTOMIZED| USER_DEFINED |
+ ---------------------------------------------------------|
+ LOCATION | HELIX | APP | APP | APP |
+ ---------------------------------------------------------|
+ STATE | HELIX | HELIX | APP | APP |
+ ----------------------------------------------------------
+```
+
+
+### FULL_AUTO
+
+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.
+
+For example, consider this system that uses a MasterSlave state model, with 3 partitions and 2 replicas in the ideal state.
+
+```
+{
+ "id" : "MyResource",
+ "simpleFields" : {
+ "REBALANCE_MODE" : "FULL_AUTO",
+ "NUM_PARTITIONS" : "3",
+ "REPLICAS" : "2",
+ "STATE_MODEL_DEF_REF" : "MasterSlave",
+ }
+ "listFields" : {
+ "MyResource_0" : [],
+ "MyResource_1" : [],
+ "MyResource_2" : []
+ },
+ "mapFields" : {
+ }
+}
+```
+
+If there are 3 nodes in the cluster, then Helix will balance the masters and slaves equally. The ideal state is therefore:
+
+```
+{
+ "id" : "MyResource",
+ "simpleFields" : {
+ "NUM_PARTITIONS" : "3",
+ "REPLICAS" : "2",
+ "STATE_MODEL_DEF_REF" : "MasterSlave",
+ },
+ "mapFields" : {
+ "MyResource_0" : {
+ "N1" : "MASTER",
+ "N2" : "SLAVE",
+ },
+ "MyResource_1" : {
+ "N2" : "MASTER",
+ "N3" : "SLAVE",
+ },
+ "MyResource_2" : {
+ "N3" : "MASTER",
+ "N1" : "SLAVE",
+ }
+ }
+}
+```
+
+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..
+
+### SEMI_AUTO
+
+When the application needs to control the placement of the replicas, use the SEMI_AUTO rebalance mode.
+
+Example: In the ideal state below, the partition \'MyResource_0\' is constrained to be placed only on node1 or node2. The choice of _state_ is still controlled by Helix. That means MyResource_0.MASTER could be on node1 and MyResource_0.SLAVE on node2, or vice-versa but neither would be placed on node3.
+
+```
+{
+ "id" : "MyResource",
+ "simpleFields" : {
+ "REBALANCE_MODE" : "SEMI_AUTO",
+ "NUM_PARTITIONS" : "3",
+ "REPLICAS" : "2",
+ "STATE_MODEL_DEF_REF" : "MasterSlave",
+ }
+ "listFields" : {
+ "MyResource_0" : [node1, node2],
+ "MyResource_1" : [node2, node3],
+ "MyResource_2" : [node3, node1]
+ },
+ "mapFields" : {
+ }
+}
+```
+
+The MasterSlave state model requires that a partition has exactly one MASTER at all times, and the other replicas should be SLAVEs. In this simple example with 2 replicas per partition, there would be one MASTER and one SLAVE. Upon failover, a SLAVE has to assume mastership, and a new SLAVE will be generated.
+
+In this mode when node1 fails, unlike in FULL_AUTO mode the partition is _not_ moved from node1 to node3. Instead, Helix will decide to change the state of MyResource_0 on node2 from SLAVE to MASTER, based on the system constraints.
+
+### CUSTOMIZED
+
+Helix offers a third mode called CUSTOMIZED, in which the application controls the placement _and_ 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 _Idealstate_ and _Currentstate_ converges.
+
+Here\'s an example, again with 3 partitions, 2 replicas per partition, and the MasterSlave state model:
+
+```
+{
+ "id" : "MyResource",
+ "simpleFields" : {
+ "REBALANCE_MODE" : "CUSTOMIZED",
+ "NUM_PARTITIONS" : "3",
+ "REPLICAS" : "2",
+ "STATE_MODEL_DEF_REF" : "MasterSlave",
+ },
+ "mapFields" : {
+ "MyResource_0" : {
+ "N1" : "MASTER",
+ "N2" : "SLAVE",
+ },
+ "MyResource_1" : {
+ "N2" : "MASTER",
+ "N3" : "SLAVE",
+ },
+ "MyResource_2" : {
+ "N3" : "MASTER",
+ "N1" : "SLAVE",
+ }
+ }
+}
+```
+
+Suppose the current state of the system is 'MyResource_0' -> {N1:MASTER, N2:SLAVE} and the application changes the ideal state to 'MyResource_0' -> {N1:SLAVE,N2:MASTER}. While the application decides which node is MASTER and which is SLAVE, Helix will not blindly issue MASTER-->SLAVE to N1 and SLAVE-->MASTER to N2 in parallel, since that might result in a transient state where both N1 and N2 are masters, which violates the MasterSlave constraint that there is exactly one MASTER at a time. Helix will first issue MASTER-->SLAVE to N1 and after it is completed, it will issue SLAVE-->MASTER to N2.
+
+### USER_DEFINED
+
+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 [User-Defined Rebalancer](./tutorial_user_def_rebalancer.html).
+
+### Backwards Compatibility
+
+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.
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_spectator.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Spectator</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Spectator
+
+Next, we\'ll learn how to implement a __spectator__. Typically, a spectator needs to react to changes within the distributed system. Examples: a client that needs to know where to send a request, a topic consumer in a consumer group. The spectator is automatically informed of changes in the _external state_ of the cluster, but it does not have to add any code to keep track of other components in the system.
+
+### Start a Connection
+
+Same as for a participant, The Helix manager is the common component that connects each system component with the cluster.
+
+It requires the following parameters:
+
+* clusterName: A logical name to represent the group of nodes
+* instanceName: A logical name of the process creating the manager instance. Generally this is host:port
+* instanceType: Type of the process. This can be one of the following types, in this case, use SPECTATOR:
+ * CONTROLLER: Process that controls the cluster, any number of controllers can be started but only one will be active at any given time
+ * PARTICIPANT: Process that performs the actual task in the distributed system
+ * SPECTATOR: Process that observes the changes in the cluster
+ * ADMIN: To carry out system admin actions
+* zkConnectString: Connection string to ZooKeeper. This is of the form host1:port1,host2:port2,host3:port3
+
+After the Helix manager instance is created, the only thing that needs to be registered is the listener. When the ExternalView changes, the listener is notified.
+
+A spectator observes the cluster and is notified when the state of the system changes. Helix consolidates the state of entire cluster in one Znode called ExternalView.
+Helix provides a default implementation RoutingTableProvider that caches the cluster state and updates it when there is a change in the cluster.
+
+```
+manager = HelixManagerFactory.getZKHelixManager(clusterName,
+ instanceName,
+ InstanceType.SPECTATOR,
+ zkConnectString);
+manager.connect();
+RoutingTableProvider routingTableProvider = new RoutingTableProvider();
+manager.addExternalViewChangeListener(routingTableProvider);
+```
+
+### Spectator Code
+
+In the following code snippet, the application sends the request to a valid instance by interrogating the external view. Suppose the desired resource for this request is in the partition myDB_1.
+
+```
+// instances = routingTableProvider.getInstances(, "PARTITION_NAME", "PARTITION_STATE");
+instances = routingTableProvider.getInstances("myDB", "myDB_1", "ONLINE");
+
+////////////////////////////////////////////////////////////////////////////////////////////////
+// Application-specific code to send a request to one of the instances //
+////////////////////////////////////////////////////////////////////////////////////////////////
+
+theInstance = instances.get(0); // should choose an instance and throw an exception if none are available
+result = theInstance.sendRequest(yourApplicationRequest, responseObject);
+
+```
+
+When the external view changes, the application needs to react by sending requests to a different instance.
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_state.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - State Machine Configuration</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): State Machine Configuration
+
+In this chapter, we\'ll learn about the state models provided by Helix, and how to create your own custom state model.
+
+### State Models
+
+Helix comes with 3 default state models that are commonly used. It is possible to have multiple state models in a cluster.
+Every resource that is added should be configured to use a state model that govern its _ideal state_.
+
+#### MASTER-SLAVE
+
+* 3 states: OFFLINE, SLAVE, MASTER
+* Maximum number of masters: 1
+* Slaves are based on the replication factor. The replication factor can be specified while adding the resource.
+
+
+#### ONLINE-OFFLINE
+
+* Has 2 states: OFFLINE and ONLINE. This simple state model is a good starting point for most applications.
+
+#### LEADER-STANDBY
+
+* 1 Leader and multiple stand-bys. The idea is that exactly one leader accomplishes a designated task, the stand-bys are ready to take over if the leader fails.
+
+### Constraints
+
+In addition to the state machine configuration, one can specify the constraints of states and transitions.
+
+For example, one can say:
+
+* MASTER:1
+<br/>Maximum number of replicas in MASTER state at any time is 1
+
+* OFFLINE-SLAVE:5
+<br/>Maximum number of OFFLINE-SLAVE transitions that can happen concurrently in the system is 5 in this example.
+
+#### Dynamic State Constraints
+
+We also support two dynamic upper bounds for the number of replicas in each state:
+
+* N: The number of replicas in the state is at most the number of live participants in the cluster
+* R: The number of replicas in the state is at most the specified replica count for the partition
+
+#### State Priority
+
+Helix uses a greedy approach to satisfy the state constraints. For example, if the state machine configuration says it needs 1 MASTER and 2 SLAVES, but only 1 node is active, Helix must promote it to MASTER. This behavior is achieved by providing the state priority list as \[MASTER, SLAVE\].
+
+#### State Transition Priority
+
+Helix tries to fire as many transitions as possible in parallel to reach the stable state without violating constraints. By default, Helix simply sorts the transitions alphabetically and fires as many as it can without violating the constraints. You can control this by overriding the priority order.
+
+### Special States
+
+There are a few Helix-defined states that are important to be aware of.
+
+#### DROPPED
+
+The DROPPED state is used to signify a replica that was served by a given participant, but is no longer served. This allows Helix and its participants to effectively clean up. There are two requirements that every new state model should follow with respect to the DROPPED state:
+
+* The DROPPED state must be defined
+* There must be a path to DROPPED for every state in the model
+
+#### ERROR
+
+The ERROR state is used whenever the participant serving a partition encountered an error and cannot continue to serve the partition. HelixAdmin has \"reset\" functionality to allow for participants to recover from the ERROR state.
+
+### Annotated Example
+
+Below is a complete definition of a Master-Slave state model. Notice the fields marked REQUIRED; these are essential for any state model definition.
+
+```
+StateModelDefinition stateModel = new StateModelDefinition.Builder("MasterSlave")
+ // OFFLINE is the state that the system starts in (initial state is REQUIRED)
+ .initialState("OFFLINE")
+
+ // Lowest number here indicates highest priority, no value indicates lowest priority
+ .addState("MASTER", 1)
+ .addState("SLAVE", 2)
+ .addState("OFFLINE")
+
+ // Note the special inclusion of the DROPPED state (REQUIRED)
+ .addState(HelixDefinedState.DROPPED.toString())
+
+ // No more than one master allowed
+ .upperBound("MASTER", 1)
+
+ // R indicates an upper bound of number of replicas for each partition
+ .dynamicUpperBound("SLAVE", "R")
+
+ // Add some high-priority transitions
+ .addTransition("SLAVE", "MASTER", 1)
+ .addTransition("OFFLINE", "SLAVE", 2)
+
+ // Using the same priority value indicates that these transitions can fire in any order
+ .addTransition("MASTER", "SLAVE", 3)
+ .addTransition("SLAVE", "OFFLINE", 3)
+
+ // Not specifying a value defaults to lowest priority
+ // Notice the inclusion of the OFFLINE to DROPPED transition
+ // Since every state has a path to OFFLINE, they each now have a path to DROPPED (REQUIRED)
+ .addTransition("OFFLINE", HelixDefinedState.DROPPED.toString())
+
+ // Create the StateModelDefinition instance
+ .build();
+
+ // Use the isValid() function to make sure the StateModelDefinition will work without issues
+ Assert.assertTrue(stateModel.isValid());
+```
+
+
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/trunk/src/site/markdown/tutorial_throttling.md
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+<!---
+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.
+-->
+
+<head>
+ <title>Tutorial - Throttling</title>
+</head>
+
+## [Helix Tutorial](./Tutorial.html): Throttling
+
+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.
+
+### Throttling
+
+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.
+
+Helix allows applications to set a threshold on transitions. The threshold can be set at multiple scopes:
+
+* MessageType e.g STATE_TRANSITION
+* TransitionType e.g SLAVE-MASTER
+* Resource e.g database
+* Node i.e per-node maximum transitions in parallel
+
+