Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/11034#discussion_r52373383
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala
---
@@ -0,0 +1,233 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.streaming
+
+import java.io._
+
+import scala.collection.mutable.{ArrayBuffer, HashMap}
+import scala.io.Codec
+
+import com.google.common.base.Charsets.UTF_8
+import org.apache.hadoop.fs.{FileStatus, FileSystem, Path}
+
+import org.apache.spark.Logging
+import org.apache.spark.sql.{DataFrame, SQLContext}
+import org.apache.spark.sql.types.{StringType, StructType}
+import org.apache.spark.util.collection.OpenHashSet
+
+/**
+ * A very simple source that reads text files from the given directory as
they appear.
+ *
+ * TODO Clean up the metadata files periodically
+ */
+class FileStreamSource(
+ sqlContext: SQLContext,
+ metadataPath: String,
+ path: String,
+ dataSchema: Option[StructType],
+ providerName: String,
+ dataFrameBuilder: Array[String] => DataFrame) extends Source with
Logging {
+
+ private val fs =
FileSystem.get(sqlContext.sparkContext.hadoopConfiguration)
+ private var maxBatchId = -1
+ private val seenFiles = new OpenHashSet[String]
+
+ /** Cache files for each batch. The content of this map is also stored
in the disk. */
+ private val batchToMetadata = new HashMap[Long, Seq[String]]
+
+ {
+ // Restore statues from the metadata files
+ val existingBatchFiles = fetchAllBatchFiles()
+ if (existingBatchFiles.nonEmpty) {
+ val existingBatchIds =
existingBatchFiles.map(_.getPath.getName.toInt)
+ maxBatchId = existingBatchIds.max
+ // Recover "batchToMetadata" and "seenFiles" from existing metadata
files.
+ existingBatchIds.sorted.foreach { batchId =>
+ val files = readBatch(batchId)
+ if (files.isEmpty) {
+ // Assert that the corrupted file must be the latest metadata
file.
+ require(batchId == maxBatchId, "Invalid metadata files")
+ maxBatchId = maxBatchId - 1
+ } else {
+ batchToMetadata(batchId) = files
+ files.foreach(seenFiles.add)
+ }
+ }
+ }
+ }
+
+ /** Returns the schema of the data from this source */
+ override lazy val schema: StructType = {
+ dataSchema.getOrElse {
+ val filesPresent = fetchAllFiles()
+ if (filesPresent.isEmpty) {
+ if (providerName == "text") {
+ // Add a default schema for "text"
+ new StructType().add("value", StringType)
+ } else {
+ throw new IllegalArgumentException("No schema specified")
+ }
+ } else {
+ // There are some existing files. Use them to infer the schema
+ dataFrameBuilder(filesPresent.toArray).schema
+ }
+ }
+ }
+
+ /**
+ * Returns the maximum offset that can be retrieved from the source.
+ *
+ * `synchronized` on this method is for solving race conditions in
tests. In the normal usage,
+ * there is no race here, so the cost of `synchronized` should be rare.
+ */
+ private def fetchMaxOffset(): LongOffset = synchronized {
+ val filesPresent = fetchAllFiles()
+ val newFiles = new ArrayBuffer[String]()
+ filesPresent.foreach { file =>
+ if (!seenFiles.contains(file)) {
+ logDebug(s"new file: $file")
+ newFiles.append(file)
+ seenFiles.add(file)
+ } else {
+ logDebug(s"old file: $file")
+ }
+ }
+
+ if (newFiles.nonEmpty) {
+ maxBatchId += 1
+ writeBatch(maxBatchId, newFiles)
+ }
+
+ new LongOffset(maxBatchId)
+ }
+
+ /**
+ * For test only. Run `action` and return the current offset. When
`action` is running, the method
+ * guarantee that the current offset won't be changed and no new batch
will be emitted.
+ */
+ def currentOffset(action: => Unit = {}): LongOffset = synchronized {
+ action
+ new LongOffset(maxBatchId)
+ }
+
+ /**
+ * Returns the next batch of data that is available after `start`, if
any is available.
+ */
+ override def getNextBatch(start: Option[Offset]): Option[Batch] = {
+ val startId =
start.map(_.asInstanceOf[LongOffset].offset).getOrElse(-1L)
+ val end = fetchMaxOffset()
+ val endId = end.offset
+
+ if (startId + 1 <= endId) {
+ val files = (startId + 1 to endId).filter(_ >= 0).flatMap { batchId
=>
+ batchToMetadata.getOrElse(batchId, Nil)
+ }.toArray
+ logDebug(s"Return files from batches ${startId + 1}:$endId")
+ logDebug(s"Streaming ${files.mkString(", ")}")
+ Some(new Batch(end, dataFrameBuilder(files)))
+ }
+ else {
+ None
+ }
+ }
+
+ private def fetchAllBatchFiles(): Seq[FileStatus] = {
+ try fs.listStatus(new Path(metadataPath)) catch {
+ case _: java.io.FileNotFoundException =>
+ fs.mkdirs(new Path(metadataPath))
+ Seq.empty
+ }
+ }
+
+ private def fetchAllFiles(): Seq[String] = {
+ fs.listStatus(new Path(path))
+ .filterNot(_.getPath.getName.startsWith("_"))
+ .map(_.getPath.toUri.toString)
+ }
+
+ /**
+ * Write the metadata of a batch to disk. The file format is as follows:
+ *
+ * {{{
+ * <FileStreamSource.VERSION>
+ * START
+ * -/a/b/c
+ * -/d/e/f
+ * ...
+ * END
+ * }}}
+ *
+ * Note: <FileStreamSource.VERSION> means the value of
`FileStreamSource.VERSION`. Every file
+ * path starts with "-" so that we can know if a line is a file path
easily.
+ */
+ private def writeBatch(id: Int, files: Seq[String]): Unit = {
+ assert(files.nonEmpty, "create a new batch without any file")
+ val output = fs.create(new Path(metadataPath + "/" + id), true)
+ val writer = new PrintWriter(new OutputStreamWriter(output, UTF_8))
+ try {
+ // scalastyle:off println
+ writer.println(FileStreamSource.VERSION)
+ writer.println(FileStreamSource.START_TAG)
+ files.foreach(file => writer.println("-" + file))
+ writer.println(FileStreamSource.END_TAG)
+ // scalastyle:on println
+ } finally {
+ writer.close()
+ }
+ batchToMetadata(id) = files
+ }
+
+ /** Read the file names of the specified batch id from the metadata file
*/
+ private def readBatch(id: Int): Seq[String] = {
+ val input = fs.open(new Path(metadataPath + "/" + id))
+ try {
+ FileStreamSource.readBatch(input)
+ } finally {
+ input.close()
+ }
+ }
+}
+
+object FileStreamSource {
+
+ private val START_TAG = "START"
+ private val END_TAG = "END"
+ val VERSION = "FILESTREAM1"
--- End diff --
FILESTREAM_V1
---
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