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PairRDDAggregator.java
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PairRDDAggregator.java
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package common;
import java.util.ArrayList;
import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaSparkContext;
import scala.Tuple2;
import scala.collection.JavaConverters;
/**
* Collect key-value pairs, creating intermediate RDDs of "batches" of a given size. Once all
* entries have been processed, the intermediate RDDs are aggregated into a final single RDD. The
* intention is to support creation of RDDs from files or iterables of data which do not fit in
* memory.
*/
public class PairRDDAggregator<K, V> {
final JavaSparkContext sc;
final int numPartitions;
final int batchSize;
final ArrayList<JavaPairRDD<K, V>> batches;
ArrayList<Tuple2<K, V>> currentBatch;
public PairRDDAggregator(JavaSparkContext sc_, final int numPartitions_, final int batchSize_) {
// Expect that a full batch is a multiple of numPartitions.
assert batchSize_ % numPartitions_ == 0;
sc = sc_;
batchSize = batchSize_;
numPartitions = numPartitions_;
batches = new ArrayList<JavaPairRDD<K, V>>();
initializeBatch();
}
public void add(final K key, final V value) {
assert currentBatch != null;
currentBatch.add(new Tuple2<K, V>(key, value));
if (currentBatch.size() >= batchSize) {
// Process the batch and start again.
processBatch();
initializeBatch();
}
}
public JavaPairRDD<K, V> aggregate() {
assert currentBatch != null;
if (currentBatch.size() > 0) {
processBatch();
}
return sc.union(JavaConverters.asScalaIteratorConverter(batches.iterator()).asScala().toSeq());
}
void processBatch() {
batches.add(sc.parallelizePairs(currentBatch, numPartitions));
currentBatch = null;
}
void initializeBatch() {
assert currentBatch == null;
currentBatch = new ArrayList<Tuple2<K, V>>(batchSize);
}
}