Github user mateiz commented on a diff in the pull request:
https://github.com/apache/spark/pull/43#discussion_r10192236
--- Diff: core/src/main/scala/org/apache/spark/storage/DiskStore.scala ---
@@ -84,12 +84,27 @@ private class DiskStore(blockManager: BlockManager,
diskManager: DiskBlockManage
override def getBytes(blockId: BlockId): Option[ByteBuffer] = {
val segment = diskManager.getBlockLocation(blockId)
val channel = new RandomAccessFile(segment.file, "r").getChannel()
- val buffer = try {
- channel.map(MapMode.READ_ONLY, segment.offset, segment.length)
- } finally {
- channel.close()
+
+ val buffer =
+ // For small files, directly read rather than memory map
+ if (segment.length < 2 * 4096) {
--- End diff --
Why would this have more impact than the current memory-mapping method?
Both will lead to a bunch of seeks and filesystem operations, here when you
read the blocks, and there when you try to send them over the network.
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