Load balancing SPI provides the next best balanced node for job
execution. This SPI is used either implicitly or explicitly whenever
a job gets mapped to a node during
ComputeTask.map(List, Object)
invocation.
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, for example, affinity load balancing for some other jobs within task, then you should use
ComputeTaskAdapter. Here is an example of how your task could 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.
ComputeJob myJob = new MyFooBarJob(arg);
jobs.put(myJob, balancer.getBalancedNode(myJob, null));
}
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().toString());
}
return buf.toString();
}
}
Ignite comes with the following load balancing SPI implementations out of the box:
NOTE: this SPI (i.e. methods in this interface) should never be used directly. SPIs provide
internal view on the subsystem and is used internally by Ignite kernal. In rare use cases when
access to a specific implementation of this SPI is required - an instance of this SPI can be obtained
via
Ignite.configuration() method to check its configuration properties or call other non-SPI
methods. Note again that calling methods from this interface on the obtained instance can lead
to undefined behavior and explicitly not supported.