org.gridgain.grid.compute

Interface GridComputeLoadBalancer

All Superinterfaces:

GridMetadataAware, Serializable

All Known Implementing Classes:

GridLoadBalancerAdapter

public interface GridComputeLoadBalancer
extends GridMetadataAware

Load balancer is used for finding the best balanced node according to load balancing policy. Internally load balancer will query the GridLoadBalancingSpi to get the balanced node.

Load balancer can be used explicitly from inside GridComputeTask.map(List, Object) method when you implement GridComputeTask interface directly or use GridComputeTaskAdapter. If you use GridComputeTaskSplitAdapter then load balancer is accessed implicitly by the adapter so you don't have to use it directly in your logic.

Coding Examples

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

 public class MyFooBarTask extends GridComputeTaskSplitAdapter<String> {
     @Override
     protected Collection<? extends GridComputeJob> split(int gridSize, String arg) throws GridException {
         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 GridComputeTaskAdapter. 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 GridComputeTaskAdapter<String, String> {
     // Inject load balancer.
     @GridLoadBalancerResource
     GridComputeLoadBalancer balancer;

     // Map jobs to grid nodes.
     public Map<? extends GridComputeJob, GridNode> map(List<GridNode> subgrid, String arg) throws GridException {
         Map<MyFooBarJob, GridNode> jobs = new HashMap<MyFooBarJob, GridNode>(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.
             GridComputeJob myJob = new MyFooBarJob(arg);

             jobs.put(myJob, balancer.getBalancedNode(myJob, null));
         }

         return jobs;
     }

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

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

         return buf.toString();
     }
 }
 

Method Summary

Methods

Modifier and Type	Method and Description
GridNode	getBalancedNode(GridComputeJob job, Collection<GridNode> exclNodes) Gets the next balanced node according to the underlying load balancing policy.

Methods inherited from interface org.gridgain.grid.GridMetadataAware

addMeta, addMetaIfAbsent, addMetaIfAbsent, allMeta, copyMeta, copyMeta, hasMeta, hasMeta, meta, putMetaIfAbsent, putMetaIfAbsent, removeMeta, removeMeta, replaceMeta

Method Detail

getBalancedNode

@Nullable
GridNode getBalancedNode(GridComputeJob job,
                                @Nullable
                                Collection<GridNode> exclNodes)
                         throws GridException

Gets the next balanced node according to the underlying load balancing policy.

Parameters:

job - Job to get the balanced node for.

exclNodes - Optional collection of nodes that should be excluded from balanced nodes. If collection is null or empty - no nodes will be excluded.

Returns:

Next balanced node.

Throws:

GridException - If any error occurred when finding next balanced node.