Github user tdas commented on a diff in the pull request: https://github.com/apache/spark/pull/2366#discussion_r17916865 --- 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 -- I agree that there may be other reasons for failure to send to a remote node. Even in those cases, the current behavior of re-fetching the peer list and sending to another node, is correct. Just not the most efficient. This optimization is something that can be addressed in a future PR.
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