Package org.apache.ignite.example.compute

Class ComputePartitionQueryMapReduceExample

java.lang.Object

org.apache.ignite.example.compute.ComputePartitionQueryMapReduceExample

public class ComputePartitionQueryMapReduceExample
extends Object

This example demonstrates a partition-aware Map/Reduce pattern using the IgniteCompute.executeMapReduce(org.apache.ignite.compute.TaskDescriptor<T, R>, T) API together with the __PARTITION_ID virtual SQL column.

In the split phase, ComputePartitionQueryMapReduceExample.PersonCountByPartitionTask enumerates all partitions of the Person table via PartitionDistribution and dispatches one job per partition to the node that currently holds the primary replica. Each ComputePartitionQueryMapReduceExample.PartitionPersonCountJob filters rows with __PARTITION_ID and returns the local count. In the reduce phase the counts are summed.

Note: PartitionDistribution.primaryReplicas() captures partition locations at a point in time. If a partition is reassigned between the split and job execution, a job may run on a non-primary node, making the SQL query non-local. For guaranteed local execution use BroadcastJobTarget.table(java.lang.String) instead — see ComputeBroadcastExample for that approach.

See README.md in the examples directory for execution instructions.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ComputePartitionQueryMapReduceExample.PartitionPersonCountJob	Job that counts persons in a single partition, identified by partition ID passed as the job argument.
static class	ComputePartitionQueryMapReduceExample.PersonCountByPartitionTask	MapReduce task that counts persons across all partitions of the Person table.

Constructor Summary

Constructors

Constructor	Description
ComputePartitionQueryMapReduceExample()

Method Summary

Modifier and Type	Method	Description
static void	main(String[] args)	Main method of the example.

Methods inherited from class java.lang.Object

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

Constructor Details

ComputePartitionQueryMapReduceExample

public ComputePartitionQueryMapReduceExample()

Method Details

main

public static void main(String[] args)
                 throws Exception

Main method of the example.

Parameters:

args - The command line arguments.

Throws:

Exception - if any error occurs.