scala - 如何将完全输出模式下的流聚合保存到 Parquet？

Question

我已经使用完整模式在流数据帧上应用了聚合。为了在本地保存数据帧，我实现了 foreach下沉。我能够以文本形式保存数据框。但我需要以 Parquet 格式保存它。

val writerForText = new ForeachWriter[Row] {
    var fileWriter: FileWriter = _

    override def process(value: Row): Unit = {
      fileWriter.append(value.toSeq.mkString(","))
    }

    override def close(errorOrNull: Throwable): Unit = {
      fileWriter.close()
    }

    override def open(partitionId: Long, version: Long): Boolean = {
      FileUtils.forceMkdir(new File(s"src/test/resources/${partitionId}"))
      fileWriter = new FileWriter(new File(s"src/test/resources/${partitionId}/temp"))
      true

    }
  }

val columnName = "col1"
frame.select(count(columnName),count(columnName),min(columnName),mean(columnName),max(columnName),first(columnName), last(columnName), sum(columnName))
              .writeStream.outputMode(OutputMode.Complete()).foreach(writerForText).start()

我怎样才能做到这一点？
提前致谢!

Answer 1

To save dataframe in local, i have implemented foreach sink. I am able to save dataframe in text form. But i need to save it in parquet format.

保存流式数据集时的默认格式是... Parquet .话虽如此，您不必使用相当先进的 foreach下沉，但仅仅是 parquet .

查询可能如下:

scala> :type in
org.apache.spark.sql.DataFrame

scala> in.isStreaming
res0: Boolean = true

in.writeStream.
  option("checkpointLocation", "/tmp/checkpoint-so").
  start("/tmp/parquets")