Package org.apache.ignite.spi.loadbalancing.weightedrandom

## Class WeightedRandomLoadBalancingSpi

- java.lang.Object
- - org.apache.ignite.spi.IgniteSpiAdapter
  - - org.apache.ignite.spi.loadbalancing.weightedrandom.WeightedRandomLoadBalancingSpi

- All Implemented Interfaces:
    `IgniteSpi`, `LoadBalancingSpi`

      @IgniteSpiMultipleInstancesSupport(true)
      @IgniteSpiConsistencyChecked(optional=true)
      public class WeightedRandomLoadBalancingSpi
      extends IgniteSpiAdapter
      implements LoadBalancingSpi

  Load balancing SPI that picks a random node for job execution. Note that you can optionally assign weights to nodes, so nodes with larger weights will end up getting proportionally more jobs routed to them (see `setNodeWeight(int)` configuration property). By default all nodes get equal weight defined by `DFLT_NODE_WEIGHT` (value is `10`).

  # Coding Example

  If you are using `ComputeTaskSplitAdapter` then load balancing logic is transparent to your code and is handled automatically by the adapter. Here is an example of how your task could look:

       public class MyFooBarTask extends ComputeTaskSplitAdapter<Object, Object> {
          @Override
          protected Collection<? extends ComputeJob> split(int gridSize, Object arg) throws IgniteCheckedException {
              List<MyFooBarJob> jobs = new ArrayList<MyFooBarJob>(gridSize);

              for (int i = 0; i < gridSize; i++) {
                  jobs.add(new MyFooBarJob(arg));
              }

              // Node assignment via load balancer
              // happens automatically.
              return jobs;
          }
          ...
       }

  If you need more fine-grained control over how some jobs within task get mapped to a node and use affinity load balancing for some other jobs within task, then you should use `ComputeTaskAdapter`. Here is an example of how your task will look. Note that in this case we manually inject load balancer and use it to pick the best node. Doing it in such way would allow user to map some jobs manually and for others use load balancer.

       public class MyFooBarTask extends ComputeTaskAdapter<String, String> {
          // Inject load balancer.
          @LoadBalancerResource
          ComputeLoadBalancer balancer;

          // Map jobs to grid nodes.
          public Map<? extends ComputeJob, ClusterNode> map(List<ClusterNode> subgrid, String arg) throws IgniteCheckedException {
              Map<MyFooBarJob, ClusterNode> jobs = new HashMap<MyFooBarJob, ClusterNode>(subgrid.size());

              // In more complex cases, you can actually do
              // more complicated assignments of jobs to nodes.
              for (int i = 0; i < subgrid.size(); i++) {
                  // Pick the next best balanced node for the job.
                  jobs.put(new MyFooBarJob(arg), balancer.getBalancedNode())
              }

              return jobs;
          }

          // Aggregate results into one compound result.
          public String reduce(List<ComputeJobResult> results) throws IgniteCheckedException {
              // For the purpose of this example we simply
              // concatenate string representation of every
              // job result
              StringBuilder buf = new StringBuilder();

              for (ComputeJobResult res : results) {
                  // Append string representation of result
                  // returned by every job.
                  buf.append(res.getData().string());
              }

              return buf.string();
          }
       }

  # Configuration

  In order to use this load balancer, you should configure your grid instance to use `WeightedRandomLoadBalancingSpi` either from Spring XML file or directly. The following configuration parameters are supported:

  ## Mandatory

  This SPI has no mandatory configuration parameters.

  ## Optional

  The following configuration parameters are optional:
  - Flag that indicates whether to use weight policy or simple random policy (see `setUseWeights(boolean)`)
  - Weight of this node (see `setNodeWeight(int)`). This parameter is ignored if `setUseWeights(boolean)` is set to `false`.
  Below is Java configuration example:

       WeightedRandomLoadBalancingSpi spi = new WeightedRandomLoadBalancingSpi();

       // Configure SPI to used weighted
       // random load balancing.
       spi.setUseWeights(true);

       // Set weight for the local node.
       spi.setWeight( *);

       IgniteConfiguration cfg = new IgniteConfiguration();

       // Override default load balancing SPI.
       cfg.setLoadBalancingSpi(spi);

       // Starts grid.
       G.start(cfg);

  Here is how you can configure `WeightedRandomLoadBalancingSpi` using Spring XML configuration:

       <property name="loadBalancingSpi">
           <bean class="org.apache.ignite.spi.loadBalancing.weightedrandom.WeightedRandomLoadBalancingSpi">
               <property name="useWeights" value="true"/>
               <property name="nodeWeight" value="10"/>
           </bean>
       </property>

  For information about Spring framework visit www.springframework.org

- - ### Field Summary

    Fields
    Modifier and Type | Field | Description
    --- | --- | ---
    `static int` | `DFLT_NODE_WEIGHT` | Default weight assigned to every node if explicit one is not provided (value is `10`).
    `static String` | `NODE_WEIGHT_ATTR_NAME` | Name of node attribute used to indicate load weight of a node (value is `"ignite.node.weight.attr.name"`).

    - ### Fields inherited from class org.apache.ignite.spi.IgniteSpiAdapter

      `ignite, igniteInstanceName`

  - ### Constructor Summary

    Constructors
    Constructor | Description
    --- | ---
    `WeightedRandomLoadBalancingSpi()` |

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `ClusterNode` | `getBalancedNode​(ComputeTaskSession ses, List<ClusterNode> top, ComputeJob job)` | Gets balanced node for specified job within given task session.
    `protected List<String>` | `getConsistentAttributeNames()` | Returns back a list of attributes that should be consistent for this SPI.
    `Map<String,​Object>` | `getNodeAttributes()` | This method is called before SPI starts (before method `IgniteSpi.spiStart(String)` is called).
    `int` | `getNodeWeight()` | See `setNodeWeight(int)`.
    `boolean` | `isUseWeights()` | See `setUseWeights(boolean)`.
    `protected void` | `onContextDestroyed0()` | Method to be called in the beginning of onContextDestroyed() method.
    `protected void` | `onContextInitialized0​(IgniteSpiContext spiCtx)` | Method to be called in the end of onContextInitialized method.
    `WeightedRandomLoadBalancingSpi` | `setName​(String name)` | Sets SPI name.
    `WeightedRandomLoadBalancingSpi` | `setNodeWeight​(int nodeWeight)` | Sets weight of this node.
    `WeightedRandomLoadBalancingSpi` | `setUseWeights​(boolean isUseWeights)` | Sets a flag to indicate whether node weights should be checked when doing random load balancing.
    `void` | `spiStart​(@Nullable String igniteInstanceName)` | This method is called to start SPI.
    `void` | `spiStop()` | This method is called to stop SPI.
    `String` | `toString()`

    - ### Methods inherited from class org.apache.ignite.spi.IgniteSpiAdapter

      `addTimeoutObject, assertParameter, checkConfigurationConsistency0, clientFailureDetectionTimeout, configInfo, createSpiAttributeName, failureDetectionTimeout, failureDetectionTimeoutEnabled, failureDetectionTimeoutEnabled, getExceptionRegistry, getLocalNode, getName, getSpiContext, ignite, initFailureDetectionTimeout, injectables, injectResources, isNodeStopping, onBeforeStart, onClientDisconnected, onClientReconnected, onContextDestroyed, onContextInitialized, registerMBean, removeTimeoutObject, started, startInfo, startStopwatch, stopInfo, unregisterMBean`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface org.apache.ignite.spi.IgniteSpi

      `getName, onClientDisconnected, onClientReconnected, onContextDestroyed, onContextInitialized`

- - ### Field Detail

    - #### NODE_WEIGHT_ATTR_NAME

          public static final String NODE_WEIGHT_ATTR_NAME

      Name of node attribute used to indicate load weight of a node (value is `"ignite.node.weight.attr.name"`).
      See Also:
        `ClusterNode.attributes()`, Constant Field Values

    - #### DFLT_NODE_WEIGHT

          public static final int DFLT_NODE_WEIGHT

      Default weight assigned to every node if explicit one is not provided (value is `10`).
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### WeightedRandomLoadBalancingSpi

          public WeightedRandomLoadBalancingSpi()

  - ### Method Detail

    - #### setUseWeights

          @IgniteSpiConfiguration(optional=true)
          public WeightedRandomLoadBalancingSpi setUseWeights​(boolean isUseWeights)

      Sets a flag to indicate whether node weights should be checked when doing random load balancing. Default value is `false` which means that node weights are disregarded for load balancing logic.
      Parameters:
        `isUseWeights` - If `true` then random load is distributed according to node weights.
      Returns:
        `this` for chaining.

    - #### isUseWeights

          public boolean isUseWeights()

      See `setUseWeights(boolean)`.
      Returns:
        Maximum sparsity.

    - #### setNodeWeight

          @IgniteSpiConfiguration(optional=true)
          public WeightedRandomLoadBalancingSpi setNodeWeight​(int nodeWeight)

      Sets weight of this node. Nodes with more processing capacity should be assigned proportionally larger weight. Default value is `DFLT_NODE_WEIGHT` and is equal for all nodes.
      Parameters:
        `nodeWeight` - Weight of this node.
      Returns:
        `this` for chaining.

    - #### getNodeWeight

          public int getNodeWeight()

      See `setNodeWeight(int)`.
      Returns:
        Maximum sparsity.

    - #### getNodeAttributes

          public Map<String,​Object> getNodeAttributes()
                                                     throws IgniteSpiException

      This method is called before SPI starts (before method `IgniteSpi.spiStart(String)` is called). It allows SPI implementation to add attributes to a local node. Kernal collects these attributes from all SPI implementations loaded up and then passes it to discovery SPI so that they can be exchanged with other nodes.
      Specified by:
        `getNodeAttributes` in interface `IgniteSpi`
      Overrides:
        `getNodeAttributes` in class `IgniteSpiAdapter`
      Returns:
        Map of local node attributes this SPI wants to add.
      Throws:
        `IgniteSpiException` - Throws in case of any error.

    - #### spiStart

          public void spiStart​(@Nullable
                               @Nullable String igniteInstanceName)
                        throws IgniteSpiException

      This method is called to start SPI. After this method returns successfully kernel assumes that SPI is fully operational.
      Specified by:
        `spiStart` in interface `IgniteSpi`
      Parameters:
        `igniteInstanceName` - Name of Ignite instance this SPI is being started for (`null` for default Ignite instance).
      Throws:
        `IgniteSpiException` - Throws in case of any error during SPI start.

    - #### spiStop

          public void spiStop()
                       throws IgniteSpiException

      This method is called to stop SPI. After this method returns kernel assumes that this SPI is finished and all resources acquired by it are released.

      Note that this method can be called at any point including during recovery of failed start. It should make no assumptions on what state SPI will be in when this method is called.

      Specified by:
        `spiStop` in interface `IgniteSpi`
      Throws:
        `IgniteSpiException` - Thrown in case of any error during SPI stop.

    - #### onContextInitialized0

          protected void onContextInitialized0​(IgniteSpiContext spiCtx)
                                        throws IgniteSpiException

      Method to be called in the end of onContextInitialized method.
      Overrides:
        `onContextInitialized0` in class `IgniteSpiAdapter`
      Parameters:
        `spiCtx` - SPI context.
      Throws:
        `IgniteSpiException` - In case of errors.

    - #### onContextDestroyed0

          protected void onContextDestroyed0()

      Method to be called in the beginning of onContextDestroyed() method.
      Overrides:
        `onContextDestroyed0` in class `IgniteSpiAdapter`

    - #### getBalancedNode

          public ClusterNode getBalancedNode​(ComputeTaskSession ses,
                                             List<ClusterNode> top,
                                             ComputeJob job)

      Gets balanced node for specified job within given task session.
      Specified by:
        `getBalancedNode` in interface `LoadBalancingSpi`
      Parameters:
        `ses` - Grid task session for currently executing task.
        `top` - Topology of task nodes from which to pick the best balanced node for given job.
        `job` - Job for which to pick the best balanced node.
      Returns:
        Best balanced node for the given job within given task session.

    - #### getConsistentAttributeNames

          protected List<String> getConsistentAttributeNames()

      Returns back a list of attributes that should be consistent for this SPI. Consistency means that remote node has to have the same attribute with the same value.
      Overrides:
        `getConsistentAttributeNames` in class `IgniteSpiAdapter`
      Returns:
        List or attribute names.

    - #### setName

          public WeightedRandomLoadBalancingSpi setName​(String name)

      Sets SPI name.
      Overrides:
        `setName` in class `IgniteSpiAdapter`
      Parameters:
        `name` - SPI name.
      Returns:
        `this` for chaining.

    - #### toString

          public String toString()

      Overrides:
        `toString` in class `Object`