Merge pull request apache#12 from harishreedharan/hdfs-wal

Initial HDFS Readers and Writers implementation.

streaming/src/main/scala/org/apache/spark/streaming/storage/FileSegment.scala

@@ -0,0 +1,19 @@
+/*
+ * 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.streaming.storage
+
+private[streaming] case class FileSegment (path: String, offset: Long, length: Int)

streaming/src/main/scala/org/apache/spark/streaming/storage/HdfsUtils.scala

@@ -0,0 +1,63 @@
+/*
+ * 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.streaming.storage
+
+import org.apache.hadoop.conf.Configuration
+import org.apache.hadoop.fs.{FSDataInputStream, FSDataOutputStream, Path}
+
+private[streaming] object HdfsUtils {
+
+  def getOutputStream(path: String): FSDataOutputStream = {
+    // HDFS is not thread-safe when getFileSystem is called, so synchronize on that
+
+    val dfsPath = new Path(path)
+    val conf = new Configuration()
+    val dfs =
+      this.synchronized {
+        dfsPath.getFileSystem(conf)
+      }
+    // If the file exists and we have append support, append instead of creating a new file
+    val stream: FSDataOutputStream = {
+      if (dfs.isFile(dfsPath)) {
+        if (conf.getBoolean("hdfs.append.support", false)) {
+          dfs.append(dfsPath)
+        } else {
+          throw new IllegalStateException("File exists and there is no append support!")
+        }
+      } else {
+        dfs.create(dfsPath)
+      }
+    }
+    stream
+  }
+
+  def getInputStream(path: String): FSDataInputStream = {
+    val dfsPath = new Path(path)
+    val dfs = this.synchronized {
+      dfsPath.getFileSystem(new Configuration())
+    }
+    val instream = dfs.open(dfsPath)
+    instream
+  }
+
+  def checkState(state: Boolean, errorMsg: => String) {
+    if(!state) {
+      throw new IllegalStateException(errorMsg)
+    }
+  }
+
+}

streaming/src/main/scala/org/apache/spark/streaming/storage/WriteAheadLogRandomReader.scala

@@ -0,0 +1,46 @@
+/*
+ * 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.streaming.storage
+
+import java.io.Closeable
+
+private[streaming] class WriteAheadLogRandomReader(path: String) extends Closeable {
+
+  private val instream = HdfsUtils.getInputStream(path)
+  private var closed = false
+
+  def read(segment: FileSegment): Array[Byte] = synchronized {
+    assertOpen()
+    instream.seek(segment.offset)
+    val nextLength = instream.readInt()
+    HdfsUtils.checkState(nextLength == segment.length,
+      "Expected message length to be " + segment.length + ", " + "but was " + nextLength)
+    val buffer = new Array[Byte](nextLength)
+    instream.readFully(buffer)
+    buffer
+  }
+
+  override def close(): Unit = synchronized {
+    closed = true
+    instream.close()
+  }
+
+  private def assertOpen() {
+    HdfsUtils.checkState(!closed, "Stream is closed. Create a new Reader to read from the file.")
+  }
+}
+

streaming/src/main/scala/org/apache/spark/streaming/storage/WriteAheadLogReader.scala

@@ -0,0 +1,69 @@
+/*
+ * 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.streaming.storage
+
+import java.io.Closeable
+
+private[streaming] class WriteAheadLogReader(path: String)
+  extends Iterator[Array[Byte]] with Closeable {
+
+  private val instream = HdfsUtils.getInputStream(path)
+  private var closed = false
+  private var nextItem: Option[Array[Byte]] = None
+
+  override def hasNext: Boolean = synchronized {
+    assertOpen()
+    if (nextItem.isDefined) { // handle the case where hasNext is called without calling next
+      true
+    } else {
+      val available = instream.available()
+      if (available < 4) { // Length of next block (which is an Int = 4 bytes) of data is unavailable!
+        false
+      }
+      val length = instream.readInt()
+      if (instream.available() < length) {
+        false
+      }
+      val buffer = new Array[Byte](length)
+      instream.readFully(buffer)
+      nextItem = Some(buffer)
+      true
+    }
+  }
+
+  override def next(): Array[Byte] = synchronized {
+    // TODO: Possible error case where there are not enough bytes in the stream
+    // TODO: How to handle that?
+    val data = nextItem.getOrElse {
+      throw new IllegalStateException("next called without calling hasNext or after hasNext " +
+        "returned false")
+    }
+    nextItem = None // Ensure the next hasNext call loads new data.
+    data
+  }
+
+  override def close(): Unit = synchronized {
+    closed = true
+    instream.close()
+  }
+
+  private def assertOpen() {
+    HdfsUtils.checkState(!closed, "Stream is closed. Create a new Reader to read from the " +
+      "file.")
+  }
+
+}

streaming/src/main/scala/org/apache/spark/streaming/storage/WriteAheadLogWriter.scala

@@ -0,0 +1,47 @@
+/*
+ * 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.streaming.storage
+
+import java.io.Closeable
+
+private[streaming] class WriteAheadLogWriter(path: String) extends Closeable {
+  private val stream = HdfsUtils.getOutputStream(path)
+  private var nextOffset = stream.getPos
+  private var closed = false
+
+  // Data is always written as:
+  // - Length - Long
+  // - Data - of length = Length
+  def write(data: Array[Byte]): FileSegment = synchronized {
+    assertOpen()
+    val segment = new FileSegment(path, nextOffset, data.length)
+    stream.writeInt(data.length)
+    stream.write(data)
+    stream.hflush()
+    nextOffset = stream.getPos
+    segment
+  }
+
+  override private[streaming] def close(): Unit = synchronized {
+    closed = true
+    stream.close()
+  }
+
+  private def assertOpen() {
+    HdfsUtils.checkState(!closed, "Stream is closed. Create a new Writer to write to file.")
+  }
+}