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From JoshRosen <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-13980] Incrementally serialize blocks w...
Date Mon, 21 Mar 2016 18:46:23 GMT
Github user JoshRosen commented on a diff in the pull request:

    https://github.com/apache/spark/pull/11791#discussion_r56875075
  
    --- Diff: core/src/main/scala/org/apache/spark/storage/memory/MemoryStore.scala ---
    @@ -500,3 +601,79 @@ private[storage] class PartiallyUnrolledIterator(
         iter = null
       }
     }
    +
    +/**
    + * A wrapper which allows an open [[OutputStream]] to be redirected to a different sink.
    + */
    +private class RedirectableOutputStream extends OutputStream {
    +  private[this] var os: OutputStream = _
    +  def setOutputStream(s: OutputStream): Unit = { os = s }
    +  override def write(b: Int): Unit = os.write(b)
    +  override def write(b: Array[Byte]): Unit = os.write(b)
    +  override def write(b: Array[Byte], off: Int, len: Int): Unit = os.write(b, off, len)
    +  override def flush(): Unit = os.flush()
    +  override def close(): Unit = os.close()
    +}
    +
    +/**
    + * The result of a failed [[MemoryStore.putIteratorAsBytes()]] call.
    + *
    + * @param memoryStore the MemoryStore, used for freeing memory.
    + * @param blockManager the BlockManager, used for deserializing values.
    + * @param blockId the block id.
    + * @param serializationStream a serialization stream which writes to [[redirectableOutputStream]].
    + * @param redirectableOutputStream an OutputStream which can be redirected to a different
sink.
    + * @param unrollMemory the amount of unroll memory used by the values in `unrolled`.
    + * @param unrolled a byte buffer containing the partially-serialized values.
    + * @param rest         the rest of the original iterator passed to
    + *                     [[MemoryStore.putIteratorAsValues()]].
    + */
    +private[storage] class PartiallySerializedBlock(
    +    memoryStore: MemoryStore,
    +    blockManager: BlockManager,
    +    blockId: BlockId,
    +    serializationStream: SerializationStream,
    +    redirectableOutputStream: RedirectableOutputStream,
    +    unrollMemory: Long,
    +    unrolled: ChunkedByteBuffer,
    +    rest: Iterator[Any]) {
    +
    +  /**
    +   * Called to dispose of this block and free its memory.
    +   */
    +  def discard(): Unit = {
    +    try {
    +      serializationStream.close()
    +    } finally {
    +      memoryStore.releaseUnrollMemoryForThisTask(unrollMemory)
    +    }
    +  }
    +
    +  /**
    +   * Finish writing this block to the given output stream by first writing the serialized
values
    +   * and then serializing the values from the original input iterator.
    +   */
    +  def finishWritingToStream(os: OutputStream): Unit = {
    +    ByteStreams.copy(unrolled.toInputStream(), os)
    +    redirectableOutputStream.setOutputStream(os)
    +    while (rest.hasNext) {
    +      serializationStream.writeObject(rest.next())
    +    }
    +    serializationStream.close()
    +  }
    +
    +  /**
    +   * Returns an iterator over the values in this block by first deserializing the serialized
    +   * values and then consuming the rest of the original input iterator.
    +   *
    +   * If the caller does not plan to fully consume the resulting iterator then they must
call
    +   * `close()` on it to free its resources.
    +   */
    +  def valuesIterator: PartiallyUnrolledIterator = {
    +    new PartiallyUnrolledIterator(
    +      memoryStore,
    +      unrollMemory,
    +      unrolled = blockManager.dataDeserialize(blockId, unrolled),
    --- End diff --
    
    It's kind of a bummer that we need to pass `blockManager` in here when all that we want
to do is figure out which type of decompression and deserialization needs to be performed.
It'd be nice to loosen coupling here in a future followup patch.


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