> For the complete documentation index, see [llms.txt](https://mariadb.com/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mariadb.com/docs/gridgain/gridgain-8/gridgain8-development/distributed-computing-and-services/distributed-computing/job-scheduling.md).

# Job Scheduling

Control how jobs are scheduled for processing on each node by configuring the CollisionSpi with FIFO or priority ordering.

When jobs arrive at the destination node, they are submitted to a thread pool and scheduled for execution in random order. However, you can change job ordering by configuring `CollisionSpi`. The `CollisionSpi` interface provides a way to control how jobs are scheduled for processing on each node.

GridGain provides several implementations of the `CollisionSpi` interface:

* `FifoQueueCollisionSpi` — simple FIFO ordering in multiple threads. This implementation is used by default;
* `PriorityQueueCollisionSpi` — priority ordering;
* `JobStealingFailoverSpi` — use this implementation to enable [job stealing](/docs/gridgain/gridgain-8/gridgain8-development/distributed-computing-and-services/distributed-computing/load-balancing.md#job-stealing).

To enable a specific collision spi, change the `IgniteConfiguration.collisionSpi` property.

## FIFO Ordering

`FifoQueueCollisionSpi` provides FIFO ordering of jobs as they arrive. The jobs are executed in multiple threads. The number of threads is controlled by the `parallelJobsNumber` parameter. The default value equals 2 times the number of processor cores.

{% tabs %}
{% tab title="XML" %}

```xml
<bean class="org.apache.ignite.configuration.IgniteConfiguration">

    <property name="collisionSpi">
        <bean class="org.apache.ignite.spi.collision.fifoqueue.FifoQueueCollisionSpi">
            <!-- Execute one job at a time. -->
            <property name="parallelJobsNumber" value="1"/>
        </bean>
    </property>

</bean>
```

{% endtab %}

{% tab title="Java" %}

```java
FifoQueueCollisionSpi colSpi = new FifoQueueCollisionSpi();

// Execute jobs sequentially, one at a time,
// by setting parallel job number to 1.
colSpi.setParallelJobsNumber(1);

IgniteConfiguration cfg = new IgniteConfiguration();

// Override default collision SPI.
cfg.setCollisionSpi(colSpi);

// Start a node.
Ignite ignite = Ignition.start(cfg);
```

{% endtab %}

{% tab title="C#/.NET" %}
unsupported
{% endtab %}
{% endtabs %}

## Priority Ordering

Use `PriorityQueueCollisionSpi` to assign priorities to individual jobs, so that jobs with higher priority are executed ahead of lower priority jobs. You can also specify the number of threads to process jobs.

{% hint style="info" %}
Job and task priority configuration must be the same for all nodes in cluster.
{% endhint %}

{% tabs %}
{% tab title="XML" %}

```xml
<bean class="org.apache.ignite.configuration.IgniteConfiguration">

    <property name="collisionSpi">
        <bean class="org.apache.ignite.spi.collision.priorityqueue.PriorityQueueCollisionSpi">
            <!-- Change the parallel job number if needed. 
                 Default is number of cores times 2. -->
            <property name="parallelJobsNumber" value="5"/>

            <!-- Change the attribute key for tasks.
                 This key is used to look up task priorities from task context.
                 By default, "grid.task.priority" is used. -->
            <property name="priorityAttributeKey" value="grid.task.priority"/>

            <!-- Change the attribute key for jobs.
                 This key is used to look up job priorities from job context.
                 By default, "grid.job.priority" is used. -->
            <property name="jobPriorityAttributeKey" value="grid.job.priority"/>

            <!-- Set the default job priority.
                 By default is set to 0. -->
            <property name="defaultPriority" value="10"/>
        </bean>
    </property>

</bean>
```

{% endtab %}

{% tab title="Java" %}

```java
PriorityQueueCollisionSpi colSpi = new PriorityQueueCollisionSpi();

// Change the parallel job number if needed.
// Default is number of cores times 2.
colSpi.setParallelJobsNumber(5);

// Change the attribute key for tasks.
// This key is used to look up task priorities from task context.
// By default, "grid.task.priority" is used.
colSpi.setPriorityAttributeKey("grid.task.priority");

// Change the attribute key for jobs.
// This key is used to look up job priorities from job context.
// By default, "grid.job.priority" is used.
colSpi.setJobPriorityAttributeKey("grid.job.priority");

// Set the default job priority.
// By default is set to 0.
colSpi.setDefaultPriority(10);

IgniteConfiguration cfg = new IgniteConfiguration();

// Override default collision SPI.
cfg.setCollisionSpi(colSpi);

// Start a node.
Ignite ignite = Ignition.start(cfg);
```

{% endtab %}

{% tab title="C#/.NET" %}
unsupported
{% endtab %}

{% tab title="C++" %}
unsupported
{% endtab %}
{% endtabs %}

### Changing Specific Task Priority

Task priorities are set in the [task session](/docs/gridgain/gridgain-8/gridgain8-development/distributed-computing-and-services/distributed-computing/map-reduce.md#distributed-task-session) via the `grid.task.priority` attribute. To change it, the task`s class must have the` @ComputeTaskSessionFullSupport\` annotation. If no priority is assigned to a task, the default priority of 0 is used.

{% tabs %} {% tab title="Java" %}

```java
@ComputeTaskSessionFullSupport
public class MyUrgentTask extends ComputeTaskSplitAdapter<Object, Object> {
    // Auto-injected task session.
    @TaskSessionResource
    private ComputeTaskSession taskSes = null;

    @Override
    protected Collection<ComputeJob> split(int gridSize, Object arg) {
        // Set high task priority.
        taskSes.setAttribute("grid.task.priority", 10);

        List<ComputeJob> jobs = new ArrayList<>(gridSize);

        for (int i = 1; i <= gridSize; i++) {
            jobs.add(new ComputeJobAdapter() {

                @Override
                public Object execute() throws IgniteException {

                    //your implementation goes here

                    return null;
                }
            });
        }

        // These jobs will be executed with higher priority.
        return jobs;
    }

    @Override
    public Object reduce(List<ComputeJobResult> results) throws IgniteException {
        return null;
    }
}
```

```csharp
namespace dotnet_helloworld
{
    public class JobScheduling
    {
        public void Priority()
        {
            // PriorityQueueCollisionSpi must be configured in the Spring XML configuration file ignite-helloworld.xml
            var cfg = new IgniteConfiguration
            {
                SpringConfigUrl = "ignite-helloworld.xml"
            };

            // Start a node.
            using var ignite = Ignition.Start(cfg);
        }

        // Compute tasks must be annotated with the ComputeTaskSessionFullSupport attribute to support distributing the task's session attributes to compute jobs that the task creates.
        [ComputeTaskSessionFullSupport]
        public class MyUrgentTask : ComputeTaskSplitAdapter<int, bool, bool>
        {
            // Auto-injected task session.
            [TaskSessionResource] private IComputeTaskSession _taskSes;

            protected override ICollection<IComputeJob<bool>> Split(int gridSize, int arg)
            {
                // Set high task priority.
                _taskSes.SetAttribute("grid.task.priority", 10);

                var jobs = new List<IComputeJob<bool>>(gridSize);

                for (var i = 1; i <= gridSize; i++)
                {
                    jobs.Add(new MyUrgentJob());
                }

                // These jobs will be executed with higher priority.
                return jobs;
            }

            public override bool Reduce(IList<IComputeJobResult<bool>> results) => results.All(r => r.Data);
        }

        private class MyUrgentJob : ComputeJobAdapter<bool>
        {
            public override bool Execute() => true;
        }
    }
}
```