Github user mridulm commented on a diff in the pull request:
https://github.com/apache/spark/pull/2366#discussion_r17833363
--- Diff: core/src/main/scala/org/apache/spark/storage/BlockManager.scala
---
@@ -787,31 +789,88 @@ private[spark] class BlockManager(
}
/**
+ * Get peer block managers in the system.
+ */
+ private def getPeers(forceFetch: Boolean): HashSet[BlockManagerId] = {
+ val cachedPeersTtl = conf.getInt("spark.storage.cachedPeersTtl", 60 *
1000) // milliseconds
+ val timeout = System.currentTimeMillis - lastPeerFetchTime >
cachedPeersTtl
+
+ cachedPeers.synchronized {
+ if (cachedPeers.isEmpty || forceFetch || timeout) {
+ cachedPeers.clear()
+ cachedPeers ++= master.getPeers(blockManagerId).sortBy(_.hashCode)
+ lastPeerFetchTime = System.currentTimeMillis
+ logDebug("Fetched peers from master: " + cachedPeers.mkString("[",
",", "]"))
+ }
+ }
+ cachedPeers
+ }
+
+ /**
* Replicate block to another node.
*/
- @volatile var cachedPeers: Seq[BlockManagerId] = null
private def replicate(blockId: BlockId, data: ByteBuffer, level:
StorageLevel): Unit = {
+ val maxReplicationFailures =
conf.getInt("spark.storage.maxReplicationFailures", 1)
+ val numPeersToReplicateTo = level.replication - 1
+ val peersReplicatedTo = new HashSet[BlockManagerId]
+ val peersFailedToReplicateTo = new HashSet[BlockManagerId]
val tLevel = StorageLevel(
level.useDisk, level.useMemory, level.useOffHeap,
level.deserialized, 1)
- if (cachedPeers == null) {
- cachedPeers = master.getPeers(blockManagerId, level.replication - 1)
+ val startTime = System.nanoTime
+ val random = new Random(blockId.hashCode)
+
+ var forceFetchPeers = false
+ var failures = 0
+ var done = false
+
+ // Get a random peer
+ def getRandomPeer(): Option[BlockManagerId] = {
+ val peers = getPeers(forceFetchPeers) -- peersReplicatedTo --
peersFailedToReplicateTo
+ if (!peers.isEmpty) Some(peers.toSeq(random.nextInt(peers.size)))
else None
--- End diff --
This would mean that, assuming there is no change to number of executors in
system, we will consistently get the same peer back.
But even if some unrelated peer was added or removed, we wont get back the
same peer we cached to last time.
Did I read the correctly, or am I missing something ? Thanks.
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