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ForeachSink

ForeachSink is a typed streaming sink that passes rows (of the type T) to ForeachWriter (one record at a time per partition).

Note

ForeachSink is assigned a ForeachWriter when DataStreamWriter is started.

ForeachSink is used exclusively in foreach operator.

[source, scala]

val records = spark. readStream format("text"). load("server-logs/*.out"). as[String]

import org.apache.spark.sql.ForeachWriter val writer = new ForeachWriter[String] { override def open(partitionId: Long, version: Long) = true override def process(value: String) = println(value) override def close(errorOrNull: Throwable) = {} }

records.writeStream .queryName("server-logs processor") .foreach(writer) .start


Internally, addBatch (the only method from the <>) takes records from the input spark-sql-dataframe.md[DataFrame] (as data), transforms them to expected type T (of this ForeachSink) and (now as a spark-sql-dataset.md[Dataset]) spark-sql-dataset.md#foreachPartition[processes each partition].

[source, scala]

addBatch(batchId: Long, data: DataFrame): Unit

addBatch then opens the constructor's datasources/ForeachWriter.md[ForeachWriter] (for the spark-taskscheduler-taskcontext.md#getPartitionId[current partition] and the input batch) and passes the records to process (one at a time per partition).

CAUTION: FIXME Why does Spark track whether the writer failed or not? Why couldn't it finally and do close?

CAUTION: FIXME Can we have a constant for "foreach" for source in DataStreamWriter?


Last update: 2020-10-31