Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/17300#discussion_r114929963
--- Diff: core/src/main/scala/org/apache/spark/storage/BlockManager.scala
---
@@ -555,12 +555,15 @@ private[spark] class BlockManager(
/**
* Return a list of locations for the given block, prioritizing the
local machine since
- * multiple block managers can share the same host.
+ * multiple block managers can share the same host, followed by hosts on
the same rack.
*/
private def getLocations(blockId: BlockId): Seq[BlockManagerId] = {
val locs = Random.shuffle(master.getLocations(blockId))
val (preferredLocs, otherLocs) = locs.partition { loc =>
blockManagerId.host == loc.host }
- preferredLocs ++ otherLocs
+ val (sameRackLocs, differentRackLocs) = otherLocs.partition {
+ loc => blockManagerId.topologyInfo == loc.topologyInfo
--- End diff --
If `blockManagerId.topologyInfo` is `None`, we will prefer the locations
with empty `topologyInfo`. It is slightly different with what the shuffling
wants to do here.
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