Github user mridulm commented on a diff in the pull request:
https://github.com/apache/spark/pull/2366#discussion_r17833419
--- 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
}
- for (peer: BlockManagerId <- cachedPeers) {
- val start = System.nanoTime
- data.rewind()
- logDebug(s"Try to replicate $blockId once; The size of the data is
${data.limit()} Bytes. " +
- s"To node: $peer")
- try {
- blockTransferService.uploadBlockSync(
- peer.host, peer.port, blockId.toString, new
NioByteBufferManagedBuffer(data), tLevel)
- } catch {
- case e: Exception =>
- logError(s"Failed to replicate block to $peer", e)
+ // One by one choose a random peer and try uploading the block to it
+ // If replication fails (e.g., target peer is down), force the list of
cached peers
+ // to be re-fetched from driver and then pick another random peer for
replication. Also
+ // temporarily black list the peer for which replication failed.
+ while (!done) {
+ getRandomPeer() match {
+ case Some(peer) =>
+ try {
+ val onePeerStartTime = System.nanoTime
+ data.rewind()
+ logTrace(s"Trying to replicate $blockId of ${data.limit()}
bytes to $peer")
+ blockTransferService.uploadBlockSync(
+ peer.host, peer.port, blockId.toString, new
NioByteBufferManagedBuffer(data), tLevel)
+ logTrace(s"Replicated $blockId of ${data.limit()} bytes to
$peer in %f ms"
+ .format((System.nanoTime - onePeerStartTime) / 1e6))
+ peersReplicatedTo += peer
+ forceFetchPeers = false
+ if (peersReplicatedTo.size == numPeersToReplicateTo) {
+ done = true
+ }
+ } catch {
+ case e: Exception =>
+ logWarning(s"Failed to replicate $blockId to $peer, failure
#$failures", e)
+ failures += 1
+ forceFetchPeers = true
+ peersFailedToReplicateTo += peer
--- End diff --
Btw, curious - will replication fail only when remote peer is dead ? (and
so requiring forceFetchPeers)
What about inability to add block in remote peer ? Will that cause an
exception to be raised here ?
Eseentially I am trying to understand if Exception raised here always means
remote peer is 'dead'.
Alternative might be to list peers which have atleast
data.rewrind().remaining() space available : but we dont support that iirc (and
it can get used up before we make this call anyway I guess).
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