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<div class="subTitle">org.apache.ignite.compute</div>
<h2 title="Interface ComputeLoadBalancer" class="title">Interface ComputeLoadBalancer</h2>
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<pre>public interface <span class="strong">ComputeLoadBalancer</span></pre>
<div class="block">Load balancer is used for finding the best balanced node according
to load balancing policy. Internally load balancer will
query the <a href="../../../../org/apache/ignite/spi/loadbalancing/LoadBalancingSpi.html" title="interface in org.apache.ignite.spi.loadbalancing"><code>LoadBalancingSpi</code></a>
to get the balanced node.
<p>
Load balancer can be used <i>explicitly</i> from inside <a href="../../../../org/apache/ignite/compute/ComputeTask.html#map(java.util.List,%20T)"><code>ComputeTask.map(List, Object)</code></a>
method when you implement <a href="../../../../org/apache/ignite/compute/ComputeTask.html" title="interface in org.apache.ignite.compute"><code>ComputeTask</code></a> interface directly or use
<a href="../../../../org/apache/ignite/compute/ComputeTaskAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskAdapter</code></a>. If you use <a href="../../../../org/apache/ignite/compute/ComputeTaskSplitAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskSplitAdapter</code></a> then
load balancer is accessed <i>implicitly</i> by the adapter so you don't have
to use it directly in your logic.
<h1 class="header">Coding Examples</h1>
If you are using <a href="../../../../org/apache/ignite/compute/ComputeTaskSplitAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskSplitAdapter</code></a> 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:
<pre name="code" class="java">
public class MyFooBarTask extends ComputeTaskSplitAdapter&lt;String> {
&#64;Override
protected Collection&lt;? extends ComputeJob> split(int gridSize, String arg) throws IgniteCheckedException {
List&lt;MyFooBarJob> jobs = new ArrayList&lt;MyFooBarJob>(gridSize);
for (int i = 0; i &lt; gridSize; i++) {
jobs.add(new MyFooBarJob(arg));
}
// Node assignment via load balancer
// happens automatically.
return jobs;
}
...
}
</pre>
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
<a href="../../../../org/apache/ignite/compute/ComputeTaskAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskAdapter</code></a>. 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.
<pre name="code" class="java">
public class MyFooBarTask extends ComputeTaskAdapter&lt;String, String> {
// Inject load balancer.
&#64;LoadBalancerResource
ComputeLoadBalancer balancer;
// Map jobs to grid nodes.
public Map&lt;? extends ComputeJob, ClusterNode> map(List&lt;ClusterNode> subgrid, String arg) throws IgniteCheckedException {
Map&lt;MyFooBarJob, ClusterNode> jobs = new HashMap&lt;MyFooBarJob, ClusterNode>(subgrid.size());
// In more complex cases, you can actually do
// more complicated assignments of jobs to nodes.
for (int i = 0; i &lt; 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&lt;ComputeJobResult&gt; 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();
}
}
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<caption><span>Methods</span><span class="tabEnd">&nbsp;</span></caption>
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<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colLast" scope="col">Method and Description</th>
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<td class="colFirst"><code><a href="../../../../org/apache/ignite/cluster/ClusterNode.html" title="interface in org.apache.ignite.cluster">ClusterNode</a></code></td>
<td class="colLast"><code><strong><a href="../../../../org/apache/ignite/compute/ComputeLoadBalancer.html#getBalancedNode(org.apache.ignite.compute.ComputeJob,%20java.util.Collection)">getBalancedNode</a></strong>(<a href="../../../../org/apache/ignite/compute/ComputeJob.html" title="interface in org.apache.ignite.compute">ComputeJob</a>&nbsp;job,
<a href="http://docs.oracle.com/javase/7/docs/api/java/util/Collection.html?is-external=true" title="class or interface in java.util">Collection</a>&lt;<a href="../../../../org/apache/ignite/cluster/ClusterNode.html" title="interface in org.apache.ignite.cluster">ClusterNode</a>&gt;&nbsp;exclNodes)</code>
<div class="block">Gets the next balanced node according to the underlying load balancing policy.</div>
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<h4>getBalancedNode</h4>
<pre>@Nullable
<a href="../../../../org/apache/ignite/cluster/ClusterNode.html" title="interface in org.apache.ignite.cluster">ClusterNode</a>&nbsp;getBalancedNode(<a href="../../../../org/apache/ignite/compute/ComputeJob.html" title="interface in org.apache.ignite.compute">ComputeJob</a>&nbsp;job,
@Nullable
<a href="http://docs.oracle.com/javase/7/docs/api/java/util/Collection.html?is-external=true" title="class or interface in java.util">Collection</a>&lt;<a href="../../../../org/apache/ignite/cluster/ClusterNode.html" title="interface in org.apache.ignite.cluster">ClusterNode</a>&gt;&nbsp;exclNodes)
throws <a href="../../../../org/apache/ignite/IgniteException.html" title="class in org.apache.ignite">IgniteException</a></pre>
<div class="block">Gets the next balanced node according to the underlying load balancing policy.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>job</code> - Job to get the balanced node for.</dd><dd><code>exclNodes</code> - Optional collection of nodes that should be excluded from balanced nodes.
If collection is <code>null</code> or empty - no nodes will be excluded.</dd>
<dt><span class="strong">Returns:</span></dt><dd>Next balanced node.</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../org/apache/ignite/IgniteException.html" title="class in org.apache.ignite">IgniteException</a></code> - If any error occurred when finding next balanced node.</dd></dl>
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