Empty Iterator : Asynchronous cassandra write - scala

Question

I am trying to implement asynchronous cassandra writes on objects (not RDD) using TableWriter. Code snippet below:
class CassandraOperations[T] extends Serializable with Logging {
/**
* Saves the data from object or Iterator of object to a Cassandra table asynchronously. Uses the specified column names.
* You can check whether this action is completed or not by callback on Future.
*/
def saveToCassandraAsync(
cc: CassandraConnector,
keyspaceName: String,
tableName: String,
columns: ColumnSelector = AllColumns,
data: Iterator[T],
writeConf: WriteConf = WriteConf(ttl = TTLOption.constant(80000)))(implicit rwf: RowWriterFactory[T]):
Future[Unit] = {
implicit val ec = ExecutionContext.global
val writer = TableWriter(cc, keyspaceName, tableName, columns, writeConf)
val futureAction = Future(writer.write(TaskContext.get(), data: Iterator[T]))
futureAction
}
}
And then wait using:
Await.result(resultFuture, TIMEOUT seconds)
the data is available when the execution reaches the write method on line :
val futureAction = Future(writer.write(TaskContext.get(), data: Iterator[T]))
But data is empty when the execution reaches the definition def write(taskContext: TaskContext, **data**: Iterator[T]) of function :
def write(taskContext: TaskContext, data: Iterator[T]) {
val updater = OutputMetricsUpdater(taskContext, writeConf)
connector.withSessionDo { session =>
val protocolVersion = session.getCluster.getConfiguration.getProtocolOptions.getProtocolVersion
val rowIterator = new CountingIterator(data)
val stmt = prepareStatement(session).setConsistencyLevel(writeConf.consistencyLevel)
val queryExecutor = new QueryExecutor(
session,
writeConf.parallelismLevel,
Some(updater.batchFinished(success = true, _, _, _)),
Some(updater.batchFinished(success = false, _, _, _)))
val routingKeyGenerator = new RoutingKeyGenerator(tableDef, columnNames)
val batchType = if (isCounterUpdate) Type.COUNTER else Type.UNLOGGED
val boundStmtBuilder = new BoundStatementBuilder(
rowWriter,
stmt,
protocolVersion = protocolVersion,
ignoreNulls = writeConf.ignoreNulls)
val batchStmtBuilder = new BatchStatementBuilder(
batchType,
routingKeyGenerator,
writeConf.consistencyLevel)
val batchKeyGenerator = batchRoutingKey(session, routingKeyGenerator) _
val batchBuilder = new GroupingBatchBuilder(
boundStmtBuilder,
batchStmtBuilder,
batchKeyGenerator,
writeConf.batchSize,
writeConf.batchGroupingBufferSize,
rowIterator)
val rateLimiter = new RateLimiter((writeConf.throughputMiBPS * 1024 * 1024).toLong, 1024 * 1024)
logDebug(s"Writing data partition to $keyspaceName.$tableName in batches of ${writeConf.batchSize}.")
for (stmtToWrite <- batchBuilder) {
queryExecutor.executeAsync(stmtToWrite)
assert(stmtToWrite.bytesCount > 0)
rateLimiter.maybeSleep(stmtToWrite.bytesCount)
}
queryExecutor.waitForCurrentlyExecutingTasks()
if (!queryExecutor.successful)
throw new IOException(s"Failed to write statements to $keyspaceName.$tableName.")
val duration = updater.finish() / 1000000000d
logInfo(f"Wrote ${rowIterator.count} rows to $keyspaceName.$tableName in $duration%.3f s.")
if (boundStmtBuilder.logUnsetToNullWarning) {
logWarning(boundStmtBuilder.UnsetToNullWarning)
}
}
}
}
so I see empty iterator.
Please guide on what can be the issue.