attilapiros commented on a change in pull request #25299: [SPARK-27651][Core]
Avoid the network when shuffle blocks are fetched from the same host
URL: https://github.com/apache/spark/pull/25299#discussion_r347579858
##########
File path:
core/src/main/scala/org/apache/spark/storage/ShuffleBlockFetcherIterator.scala
##########
@@ -420,12 +447,88 @@ final class ShuffleBlockFetcherIterator(
}
}
+ private[this] def fetchHostLocalBlock(
+ blockId: BlockId,
+ mapIndex: Int,
+ localDirs: Array[String],
+ blockManagerId: BlockManagerId): Boolean = {
+ try {
+ val buf = blockManager.getHostLocalShuffleData(blockId, localDirs)
+ buf.retain()
+ results.put(SuccessFetchResult(blockId, mapIndex, blockManagerId,
buf.size(), buf,
+ isNetworkReqDone = false))
+ true
+ } catch {
+ case e: Exception =>
+ // If we see an exception, stop immediately.
+ logError(s"Error occurred while fetching local blocks", e)
+ results.put(FailureFetchResult(blockId, mapIndex, blockManagerId, e))
+ false
+ }
+ }
+
+ /**
+ * Fetch the host-local blocks while we are fetching remote blocks. This is
ok because
+ * `ManagedBuffer`'s memory is allocated lazily when we create the input
stream, so all we
+ * track in-memory are the ManagedBuffer references themselves.
+ */
+ private[this] def fetchHostLocalBlocks(hostLocalDirManager:
HostLocalDirManager): Unit = {
+ val cachedDirsByExec = hostLocalDirManager.getCachedHostLocalDirs()
+ val (hostLocalBlocksWithCachedDirs, hostLocalBlocksWithMissingDirs) =
+ hostLocalBlocksByExecutor
+ .map { case (hostLocalBmId, bmInfos) =>
+ (hostLocalBmId, bmInfos,
cachedDirsByExec.get(hostLocalBmId.executorId))
+ }.partition(_._3.isDefined)
+ val bmId = blockManager.blockManagerId
+ val immutableHostLocalBlocksWithoutDirs =
+ hostLocalBlocksWithMissingDirs.map { case (hostLocalBmId, bmInfos, _) =>
+ hostLocalBmId -> bmInfos
+ }.toMap
+ if (immutableHostLocalBlocksWithoutDirs.nonEmpty) {
+ logDebug(s"Asynchronous fetching host-local blocks without cached
executors' dir: " +
+ s"${immutableHostLocalBlocksWithoutDirs.mkString(", ")}")
+ val hostLocalDirsCompletable = new CompletableFuture[util.Map[String,
Array[String]]]()
+ hostLocalDirManager.getHostLocalDirs(
+ immutableHostLocalBlocksWithoutDirs.keys.map(_.executorId).toArray,
+ hostLocalDirsCompletable)
+ hostLocalDirsCompletable.whenComplete((dirs, throwable) => {
+ if (dirs != null ) {
+ immutableHostLocalBlocksWithoutDirs.foreach { case (hostLocalBmId,
blockInfos) =>
+ blockInfos.takeWhile { case (blockId, _, mapIndex) =>
+ fetchHostLocalBlock(
+ blockId,
+ mapIndex,
+ dirs.get(hostLocalBmId.executorId),
+ hostLocalBmId)
+ }
+ }
+ } else {
+ logError(s"Error occurred while fetching host local blocks",
throwable)
+ val (hostLocalBmId, blockInfoSeq) =
immutableHostLocalBlocksWithoutDirs.head
+ val (blockId, _, mapIndex) = blockInfoSeq.head
+ results.put(FailureFetchResult(blockId, mapIndex, hostLocalBmId,
throwable))
Review comment:
> If I'm following the code correctly, you're requiring that when this
feature is on, that all reads from the same host are made from disk, right?
Yes, you are right.
> Wouldn't it be better to allow remote requests if you detect that you're
missing this information, and replace pending remote requests with local ones
when this RPC finishes? Not sure how easy that would be though.
I think that solution would be more complex as there would be more
dependency between the threads: the one for remote fetching should be
synchronized with the one which loads the host-local blocks after getting the
directories asynchronously. And it would not be more robust: if there is no
directory registered for an executor in the external shuffle service then
remote fetching which goes the same external shuffle service would also keep
failing.
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
With regards,
Apache Git Services
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
