spark源码action系列-saveAsHadoopDataset
RDD.saveAsHadoopDataset
这个功能是spark中的saveAsTextFile,saveASHadoopFile的基础实现.
这个action用于把task中的数据通过指定的output format写入到hadoop的实现接口中,
由PairRDDFunctions类进行实现.
执行前的准备:
得到hadoopConfiguration的实例,取出OutputFormat的实现类,key,value的类.
val hadoopConf = conf
val outputFormatInstance = hadoopConf.getOutputFormat
val keyClass = hadoopConf.getOutputKeyClass
val valueClass = hadoopConf.getOutputValueClass
.....................................
SparkHadoopUtil.get.addCredentials(hadoopConf)
logDebug("Saving as hadoop file of type (" + keyClass.getSimpleName + ", " +
valueClass.getSimpleName + ")")
if (isOutputSpecValidationEnabled) {
// FileOutputFormat ignores the filesystem parameter
val ignoredFs = FileSystem.get(hadoopConf)
hadoopConf.getOutputFormat.checkOutputSpecs(ignoredFs, hadoopConf)
}
生成一个用于执行写入操作的writer实例,这个实例中包含有向hadoop写入的recordWriter.
在这里recordWriter实例还没有具体的生成.
val writer = new SparkHadoopWriter(hadoopConf)
writer.preSetup()
Task的执行的function的定义:
这里生成的writeToFile是一个需要在task中执行的function的定义.
val writeToFile = (context: TaskContext, iter: Iterator[(K, V)]) => {
1,先得到执行尝试的id.
// Hadoop wants a 32-bit task attempt ID, so if ours is bigger than
Int.MaxValue, roll it
// around by taking a mod. We expect that no task will be attempted 2 billion times.
val taskAttemptId = (context.taskAttemptId % Int.MaxValue).toInt
2,生成一个用于写入的metrics的实例.
val (outputMetrics, bytesWrittenCallback) = initHadoopOutputMetrics(context)
3,根据stageId,partition,attempt对writer进行初始化,主要是对task对应的jobId,taskid进行初始化操作.
writer.setup(context.stageId, context.partitionId, taskAttemptId)
4,这里(如果是对hdfs文件进行操作,生成对应此task的输出文件的路径),通过outputFormat生成对应的RecordWriter的实例.
writer.open()
var recordsWritten = 0L
Utils.tryWithSafeFinally {
5,这里通过对partition中的数据进行迭代,并通过recordWriter写入数据,记录metrics
while (iter.hasNext) {
val record = iter.next()
writer.write(record._1.asInstanceOf[AnyRef], record._2.asInstanceOf[AnyRef])
// Update bytes written metric every few records
maybeUpdateOutputMetrics(bytesWrittenCallback, outputMetrics, recordsWritten)
recordsWritten += 1
}
} {
执行对iterator的写入操作后,关闭recordWriter的实例,也就是调用其关闭函数.
writer.close()
}
根据mapred.output.committer.class配置的OutputCommitter实现,执行commitTask操作.
writer.commit()
bytesWrittenCallback.foreach { fn => outputMetrics.setBytesWritten(fn()) }
outputMetrics.setRecordsWritten(recordsWritten)
}
这里通过runJob并把上面生成的函数传进去,执行task
self.context.runJob(self, writeToFile)
任务结束后的处理:
根据mapred.output.committer.class配置的OutputCommitter实现,执行commitJob操作.
writer.commitJob()