Broadcast join in spark

Broadcast join in spark is a map-side join which can be used when the size of one dataset is below spark.sql.autoBroadcastJoinThreshold. Broadcast join is very efficient for joins between a large dataset with a small dataset. It can avoid sending all data of the large table over the network. To use this feature we can use broadcast function or broadcast hint to mark a dataset to broadcast when used in a join query.


import static org.apache.spark.sql.functions.broadcast;
import static org.apache.spark.sql.functions.col;
import java.util.Arrays;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.SaveMode;
import org.apache.spark.sql.SparkSession;

public class BroadCastSparkJoin {

public static void main(String[] args) {

SparkSession session = SparkSession.builder()
.config("spark.hadoop.fs.s3a.impl", "org.apache.hadoop.fs.s3a.S3AFileSystem")
.config("spark.hadoop.fs.s3a.access.key", "access_key_amazon")
.config("spark.hadoop.fs.s3a.secret.key", "secret_key_amazon").config("spark.speculation", "false")
.config("fs.s3a.connection.ssl.enabled", "false").config("spark.network.timeout", "600s")
.config("spark.sql.codegen.wholeStage", "false").config("spark.executor.heartbeatInterval", "500s")
.config("spark.serializer", "org.apache.spark.serializer.KryoSerializer")
.config("mapreduce.fileoutputcommitter.algorithm.version", "2").getOrCreate();

scala.collection.Seq<String> paths = com.wdc.ddp.utility.Util.javaListToScalaSeq(Arrays.asList(args));
Dataset<Row> largeDataSet = session.read().format("com.databricks.spark.avro").load(paths);
Dataset<Row> smallDataSet = session.read().format("com.databricks.spark.avro").load("small_data_path");
Dataset<Row> joinedDataset = largeDataSet
.join(broadcast(smallDataSet),
col("largeDataSet .column1").equalTo(col("smallDataSet .column1"))
.and(col("largeDataSet .column2").equalTo(col("smallDataSet .column2")))
.and(col("largeDataSet .column3").equalTo(col("smallDataSet .column3")))
.and((col("largeDataSet .column4").equalTo(col("smallDataSet .column4")))))
.select(col("largeDataSet .*"));

joinedDataset.write().mode(SaveMode.Overwrite).format("com.databricks.spark.avro").save();

}

}

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