ndolgov

interface ObjectStoreTx {
    CompletableFuture<Void> execute(TxContext ctx);

    Optional<Throwable> rollback();
}

public final class CompletableFutureSaga {
    private CompletableFuture<TxContext> executeHeadTx(Iterator<ObjectStoreTx> txs, TxContext ctx) {
        if (!txs.hasNext()) {
            return CompletableFuture.completedFuture(ctx);

ndolgov

import org.apache.spark.sql.SparkSession;

public class SparkDriver {
    public static void main(String[] args) {
        final SparkSession session = SparkSession.builder().
            appName("MySparkApp" + System.currentTimeMillis()).
            master(SparkEnvCfg.sparkMasterUrl()).
            config(SparkEnvCfg.SPARK_EXECUTOR_MEMORY, "1g").
            config(SparkEnvCfg.SPARK_SERIALIZER, SparkEnvCfg.KRYO).
            config(SparkEnvCfg.SPARK_SQL_SHUFFLE_PARTITIONS, "2").

ndolgov

public void readAndCache(SQLContext sqlCtx, File file) {
    final DataFrame df = sqlCtx.read().parquet("file://" + file.getAbsolutePath())
    sqlCtx.registerDataFrameAsTable(df, name);
    sqlCtx.cacheTable(name); // != df.persist(StorageLevel.MEMORY_ONLY_SER()) when reading from a Parquet file
    
    final long rowCount = df.count(); // warm-up cache
}