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HDFS-8008. Support client-side back off when the datanodes are congested. Contributed by Haohui Mai.

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This commit is contained in:
Haohui Mai 2015-04-01 16:54:46 -07:00
parent 75cb1d42ab
commit 6ccf4fbf8a
4 changed files with 112 additions and 0 deletions
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3
hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
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@ -868,6 +868,9 @@ Release 2.7.0 - UNRELEASED
HDFS-7742. Favoring decommissioning node for replication can cause a block
to stay underreplicated for long periods (Nathan Roberts via kihwal)
HDFS-8008. Support client-side back off when the datanodes are congested.
(wheat9)
OPTIMIZATIONS
HDFS-7454. Reduce memory footprint for AclEntries in NameNode.

63
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DataStreamer.java
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@ -218,6 +218,13 @@ private static void releaseBuffer(List<DFSPacket> packets, ByteArrayManager bam)
private boolean failPacket = false;
private final long dfsclientSlowLogThresholdMs;
private long artificialSlowdown = 0;
// List of congested data nodes. The stream will back off if the DataNodes
// are congested
private final ArrayList<DatanodeInfo> congestedNodes = new ArrayList<>();
private static final int CONGESTION_BACKOFF_MEAN_TIME_IN_MS = 5000;
private static final int CONGESTION_BACK_OFF_MAX_TIME_IN_MS =
CONGESTION_BACKOFF_MEAN_TIME_IN_MS * 10;
private int lastCongestionBackoffTime;
private final LoadingCache<DatanodeInfo, DatanodeInfo> excludedNodes;
@ -386,6 +393,11 @@ public void run() {
one = createHeartbeatPacket();
assert one != null;
} else {
try {
backOffIfNecessary();
} catch (InterruptedException e) {
DFSClient.LOG.warn("Caught exception ", e);
}
one = dataQueue.getFirst(); // regular data packet
long parents[] = one.getTraceParents();
if (parents.length > 0) {
@ -815,9 +827,14 @@ public void run() {
long seqno = ack.getSeqno();
// processes response status from datanodes.
ArrayList<DatanodeInfo> congestedNodesFromAck = new ArrayList<>();
for (int i = ack.getNumOfReplies()-1; i >=0 && dfsClient.clientRunning; i--) {
final Status reply = PipelineAck.getStatusFromHeader(ack
.getHeaderFlag(i));
if (PipelineAck.getECNFromHeader(ack.getHeaderFlag(i)) ==
PipelineAck.ECN.CONGESTED) {
congestedNodesFromAck.add(targets[i]);
}
// Restart will not be treated differently unless it is
// the local node or the only one in the pipeline.
if (PipelineAck.isRestartOOBStatus(reply) &&
@ -839,6 +856,18 @@ public void run() {
}
}
if (!congestedNodesFromAck.isEmpty()) {
synchronized (congestedNodes) {
congestedNodes.clear();
congestedNodes.addAll(congestedNodesFromAck);
}
} else {
synchronized (congestedNodes) {
congestedNodes.clear();
lastCongestionBackoffTime = 0;
}
}
assert seqno != PipelineAck.UNKOWN_SEQNO :
"Ack for unknown seqno should be a failed ack: " + ack;
if (seqno == DFSPacket.HEART_BEAT_SEQNO) { // a heartbeat ack
@ -1543,6 +1572,40 @@ private LocatedBlock locateFollowingBlock(DatanodeInfo[] excludedNodes)
}
}
/**
* This function sleeps for a certain amount of time when the writing
* pipeline is congested. The function calculates the time based on a
* decorrelated filter.
*
* @see
* <a href="http://www.awsarchitectureblog.com/2015/03/backoff.html">
* http://www.awsarchitectureblog.com/2015/03/backoff.html</a>
*/
private void backOffIfNecessary() throws InterruptedException {
int t = 0;
synchronized (congestedNodes) {
if (!congestedNodes.isEmpty()) {
StringBuilder sb = new StringBuilder("DataNode");
for (DatanodeInfo i : congestedNodes) {
sb.append(' ').append(i);
}
int range = Math.abs(lastCongestionBackoffTime * 3 -
CONGESTION_BACKOFF_MEAN_TIME_IN_MS);
int base = Math.min(lastCongestionBackoffTime * 3,
CONGESTION_BACKOFF_MEAN_TIME_IN_MS);
t = Math.min(CONGESTION_BACK_OFF_MAX_TIME_IN_MS,
(int)(base + Math.random() * range));
lastCongestionBackoffTime = t;
sb.append(" are congested. Backing off for ").append(t).append(" ms");
DFSClient.LOG.info(sb.toString());
congestedNodes.clear();
}
}
if (t != 0) {
Thread.sleep(t);
}
}
/**
* get the block this streamer is writing to
*

4
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/datatransfer/PipelineAck.java
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@ -257,6 +257,10 @@ public static Status getStatusFromHeader(int header) {
return StatusFormat.getStatus(header);
}
public static ECN getECNFromHeader(int header) {
return StatusFormat.getECN(header);
}
public static int setStatusForHeader(int old, Status status) {
return StatusFormat.setStatus(old, status);
}

42
hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSOutputStream.java
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@ -17,20 +17,31 @@
*/
package org.apache.hadoop.hdfs;
import java.io.DataOutputStream;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.concurrent.atomic.AtomicReference;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
import org.apache.hadoop.hdfs.protocol.HdfsFileStatus;
import org.apache.hadoop.hdfs.protocol.datatransfer.BlockConstructionStage;
import org.junit.AfterClass;
import org.junit.Assert;
import org.junit.BeforeClass;
import org.junit.Test;
import org.mockito.internal.util.reflection.Whitebox;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.doThrow;
import static org.mockito.Mockito.when;
public class TestDFSOutputStream {
static MiniDFSCluster cluster;
@ -100,6 +111,37 @@ public void testComputePacketChunkSize()
Assert.assertTrue((Integer) field.get(dos) + 257 < packetSize);
}
@Test
public void testCongestionBackoff() throws IOException {
DFSClient.Conf dfsClientConf = mock(DFSClient.Conf.class);
DFSClient client = mock(DFSClient.class);
when(client.getConf()).thenReturn(dfsClientConf);
client.clientRunning = true;
DataStreamer stream = new DataStreamer(
mock(HdfsFileStatus.class),
mock(ExtendedBlock.class),
client,
"foo", null, null, null, null);
DataOutputStream blockStream = mock(DataOutputStream.class);
doThrow(new IOException()).when(blockStream).flush();
Whitebox.setInternalState(stream, "blockStream", blockStream);
Whitebox.setInternalState(stream, "stage",
BlockConstructionStage.PIPELINE_CLOSE);
@SuppressWarnings("unchecked")
LinkedList<DFSPacket> dataQueue = (LinkedList<DFSPacket>)
Whitebox.getInternalState(stream, "dataQueue");
@SuppressWarnings("unchecked")
ArrayList<DatanodeInfo> congestedNodes = (ArrayList<DatanodeInfo>)
Whitebox.getInternalState(stream, "congestedNodes");
congestedNodes.add(mock(DatanodeInfo.class));
DFSPacket packet = mock(DFSPacket.class);
when(packet.getTraceParents()).thenReturn(new long[] {});
dataQueue.add(packet);
stream.run();
Assert.assertTrue(congestedNodes.isEmpty());
}
@AfterClass
public static void tearDown() {
cluster.shutdown();