adding partitions dynamically in WebSphere JSR 352

Question

MY source table is having 10 records and I need to read 10 records and needs to process those and needs to write that processed records to the target table. For this 10 records I have created 2 partitions. But in my real project we don't know how many records daily i need to process so how can I decide that how many partitions do i need? Is it possible to add partitions dynamically? Please find my poc code at JSR 352 with Liberty Profile - how to implement checkpointing when ItemReader does a DB query.

Answer 1

Use a PartitionMapper to dynamically define the number of partitions in a partitioned step.

This runs at the beginning of the step and builds a PartitionPlan which defines the number of partitions and the Properties for each partition.

In the XML, your <partition> element should include a child <mapper> element rather than the child <plan> element you'd use to define the number of partitions statically.

But you otherwise perform the substitution similarly using the partitionPlan property substitution.

E.g.

    <step id="mappedStep">
        <batchlet ref="MyBatchlet">
            <properties>
                <property name="xx" value="#{partitionPlan['xx']}" />
            </properties>
        </batchlet>
        <partition>
            <mapper ref="MyMapper">
                <properties>
                    <property name="mapperProp" value="#{jobProperties['mapperProp']}" />
                </properties>
            </mapper>
        </partition>
    </step>

Your PartitionMapper could build the PartitionPlan with something like this:

import javax.batch.api.partition.PartitionMapper;
import javax.batch.api.partition.PartitionPlan;
import javax.batch.api.partition.PartitionPlanImpl;

// ...
@Named("MyMapper")
public class MyPartitionMapper implements PartitionMapper {

    @Inject @BatchProperty
    String mapperProp;      // FROM JSL, USE IF YOU WANT, NOT USED HERE

    @Override
    public PartitionPlan mapPartitions() throws Exception {

        numPartitions = calculateNumPartitions() // YOUR LOGIC HERE

        Properties[] props = new Properties[numPartitions];

        Integer i;
         for (i = 0; i < numPartitions; i++) {
            props[i] = new Properties();
            props[i].setProperty("xx", "xxVal" + i);  // SUPPLY PER-PARTITION PROPERTY 'xx'
            props[i].setProperty("yy", "yyVal" + i);  // SUPPLY PER-PARTITION PROPERTY 'yy'
        }

        PartitionPlan partitionPlan = new PartitionPlanImpl();
        partitionPlan.setPartitions(numPartitions);
        partitionPlan.setPartitionProperties(props);
        partitionPlan.setPartitionsOverride(false);

        return partitionPlan;       
    }
}