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From harishreedharan <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-11141][STREAMING] Batch ReceivedBlockTr...
Date Thu, 05 Nov 2015 23:26:37 GMT
Github user harishreedharan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/9143#discussion_r44085133
  
    --- Diff: streaming/src/main/scala/org/apache/spark/streaming/util/BatchedWriteAheadLog.scala
---
    @@ -0,0 +1,212 @@
    +/*
    + * 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.util
    +
    +import java.nio.ByteBuffer
    +import java.util.concurrent.{LinkedBlockingQueue, TimeoutException}
    +import java.util.{Iterator => JIterator}
    +
    +import scala.collection.JavaConverters._
    +import scala.collection.mutable.ArrayBuffer
    +import scala.concurrent.{Await, ExecutionContext, Promise}
    +import scala.concurrent.duration._
    +import scala.util.control.NonFatal
    +
    +import org.apache.spark.Logging
    +import org.apache.spark.util.{Utils, ThreadUtils}
    +
    +/**
    + * A wrapper for a WriteAheadLog that batches records before writing data. All other
methods will
    + * be passed on to the wrapped class.
    + *
    + * Parent exposed for testing.
    + */
    +private[streaming] class BatchedWriteAheadLog(private[util] val parent: WriteAheadLog)
    +  extends WriteAheadLog with Logging {
    +
    +  import BatchedWriteAheadLog._
    +
    +  // exposed for tests
    +  protected val walWriteQueue = new LinkedBlockingQueue[RecordBuffer]()
    +
    +  private val WAL_WRITE_STATUS_TIMEOUT = 5000 // 5 seconds
    +
    +  // Whether the writer thread is active
    +  @volatile private var active: Boolean = true
    +  protected val buffer = new ArrayBuffer[RecordBuffer]()
    +
    +  private val batchedWriterThread = startBatchedWriterThread()
    +
    +  /**
    +   * Write a byte buffer to the log file. This method adds the byteBuffer to a queue
and blocks
    +   * until the record is properly written by the parent.
    +   */
    +  override def write(byteBuffer: ByteBuffer, time: Long): WriteAheadLogRecordHandle =
{
    +    val promise = Promise[WriteAheadLogRecordHandle]()
    +    walWriteQueue.offer(RecordBuffer(byteBuffer, time, promise))
    +    try {
    +      Await.result(promise.future.recover { case _ => null }(ThreadUtils.sameThread),
    +        WAL_WRITE_STATUS_TIMEOUT.milliseconds)
    +    } catch {
    +      case e: TimeoutException =>
    +        logWarning(s"Write to Write Ahead Log promise timed out after " +
    +          s"$WAL_WRITE_STATUS_TIMEOUT millis for record.")
    +        null
    +    }
    +  }
    +
    +  /**
    +   * Read a segment from an existing Write Ahead Log. The data may be aggregated, and
the user
    +   * should de-aggregate using [[BatchedWriteAheadLog.deaggregate]]
    +   *
    +   * This method is handled by the parent WriteAheadLog.
    +   */
    +  override def read(segment: WriteAheadLogRecordHandle): ByteBuffer = {
    +    parent.read(segment)
    +  }
    +
    +  /**
    +   * Read all the existing logs from the log directory.
    +   *
    +   * This method is handled by the parent WriteAheadLog.
    +   */
    +  override def readAll(): JIterator[ByteBuffer] = {
    +    parent.readAll().asScala.flatMap(deaggregate).asJava
    +  }
    +
    +  /**
    +   * Delete the log files that are older than the threshold time.
    +   *
    +   * This method is handled by the parent WriteAheadLog.
    +   */
    +  override def clean(threshTime: Long, waitForCompletion: Boolean): Unit = {
    +    parent.clean(threshTime, waitForCompletion)
    +  }
    +
    +
    +  /**
    +   * Stop the batched writer thread, fulfill promises with failures and close parent
writer.
    +   */
    +  override def close(): Unit = {
    +    logInfo("BatchedWriteAheadLog shutting down.")
    +    active = false
    +    batchedWriterThread.interrupt()
    +    batchedWriterThread.join()
    +    fulfillPromises()
    +    parent.close()
    +  }
    +
    +  /**
    +   * Respond to any promises that may have been left in the queue, to unblock receivers
during
    +   * shutdown.
    +   */
    +  private def fulfillPromises(): Unit = {
    +    while (!walWriteQueue.isEmpty) {
    +      val RecordBuffer(_, _, promise) = walWriteQueue.poll()
    +      promise.success(null)
    +    }
    +  }
    +
    +  /** Start the actual log writer on a separate thread. Visible (protected) for testing.
*/
    +  protected def startBatchedWriterThread(): Thread = {
    +    val thread = new Thread(new Runnable {
    +      override def run(): Unit = {
    +        while (active) {
    +          try {
    +            flushRecords()
    +          } catch {
    +            case NonFatal(e) =>
    +              logWarning("Encountered exception in Batched Writer Thread.", e)
    +          }
    +        }
    +        logInfo("Batched WAL Writer thread exiting.")
    +      }
    +    }, "Batched WAL Writer")
    +    thread.setDaemon(true)
    +    thread.start()
    +    thread
    +  }
    +
    +  /** Write all the records in the buffer to the write ahead log. Visible for testing.
*/
    +  protected def flushRecords(): Unit = {
    +    try {
    +      buffer.append(walWriteQueue.take())
    +      val numBatched = walWriteQueue.drainTo(buffer.asJava) + 1
    +      logDebug(s"Received $numBatched records from queue")
    +    } catch {
    +      case _: InterruptedException =>
    +        logWarning("Batch Write Ahead Log Writer queue interrupted.")
    +    }
    +    try {
    +      var segment: WriteAheadLogRecordHandle = null
    +      if (buffer.length > 0) {
    +        logDebug(s"Batched ${buffer.length} records for Write Ahead Log write")
    +        // we take the latest record for the time to ensure that we don't clean up files
earlier
    +        // than the expiration date of the records
    --- End diff --
    
    This comment is not very clear. It would be better if you could make this clearer.


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