diff --git a/core/src/main/scala/org/apache/spark/network/ManagedBuffer.scala b/core/src/main/scala/org/apache/spark/network/ManagedBuffer.scala index a4409181ec907327e2ecdf8ad6d309931296aaa1..4c9ca97a2a6b70e2222753abd0977d77e60ce30a 100644 --- a/core/src/main/scala/org/apache/spark/network/ManagedBuffer.scala +++ b/core/src/main/scala/org/apache/spark/network/ManagedBuffer.scala @@ -66,13 +66,27 @@ sealed abstract class ManagedBuffer { final class FileSegmentManagedBuffer(val file: File, val offset: Long, val length: Long) extends ManagedBuffer { + /** + * Memory mapping is expensive and can destabilize the JVM (SPARK-1145, SPARK-3889). + * Avoid unless there's a good reason not to. + */ + private val MIN_MEMORY_MAP_BYTES = 2 * 1024 * 1024; + override def size: Long = length override def nioByteBuffer(): ByteBuffer = { var channel: FileChannel = null try { channel = new RandomAccessFile(file, "r").getChannel - channel.map(MapMode.READ_ONLY, offset, length) + // Just copy the buffer if it's sufficiently small, as memory mapping has a high overhead. + if (length < MIN_MEMORY_MAP_BYTES) { + val buf = ByteBuffer.allocate(length.toInt) + channel.read(buf, offset) + buf.flip() + buf + } else { + channel.map(MapMode.READ_ONLY, offset, length) + } } catch { case e: IOException => Try(channel.size).toOption match {