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HADOOP-15317. Improve NetworkTopology chooseRandom's loop.

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This commit is contained in:
Xiao Chen 2018-04-02 22:47:02 -07:00
parent c78cb18c61
commit 57374c4737
2 changed files with 163 additions and 20 deletions
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108
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/NetworkTopology.java
View File

@ -522,12 +522,12 @@ protected Node chooseRandom(final String scope, String excludedScope,
numOfDatanodes -= ((InnerNode)node).getNumOfLeaves();
}
}
if (numOfDatanodes == 0) {
LOG.debug("Failed to find datanode (scope=\"{}\" excludedScope=\"{}\").",
scope, excludedScope);
if (numOfDatanodes <= 0) {
LOG.debug("Failed to find datanode (scope=\"{}\" excludedScope=\"{}\")."
+ " numOfDatanodes={}",
scope, excludedScope, numOfDatanodes);
return null;
}
Node ret = null;
final int availableNodes;
if (excludedScope == null) {
availableNodes = countNumOfAvailableNodes(scope, excludedNodes);
@ -536,25 +536,99 @@ protected Node chooseRandom(final String scope, String excludedScope,
countNumOfAvailableNodes("~" + excludedScope, excludedNodes);
}
LOG.debug("Choosing random from {} available nodes on node {},"
+ " scope={}, excludedScope={}, excludeNodes={}", availableNodes,
innerNode, scope, excludedScope, excludedNodes);
+ " scope={}, excludedScope={}, excludeNodes={}. numOfDatanodes={}.",
availableNodes, innerNode, scope, excludedScope, excludedNodes,
numOfDatanodes);
Node ret = null;
if (availableNodes > 0) {
do {
int leaveIndex = r.nextInt(numOfDatanodes);
ret = innerNode.getLeaf(leaveIndex, node);
if (excludedNodes == null || !excludedNodes.contains(ret)) {
break;
} else {
LOG.debug("Node {} is excluded, continuing.", ret);
}
// We've counted numOfAvailableNodes inside the lock, so there must be
// at least 1 satisfying node. Keep trying until we found it.
} while (true);
ret = chooseRandom(innerNode, node, excludedNodes, numOfDatanodes,
availableNodes);
}
LOG.debug("chooseRandom returning {}", ret);
return ret;
}
/**
* Randomly choose one node under <i>parentNode</i>, considering the exclude
* nodes and scope. Should be called with {@link #netlock}'s readlock held.
*
* @param parentNode the parent node
* @param excludedScopeNode the node corresponding to the exclude scope.
* @param excludedNodes a collection of nodes to be excluded from
* @param totalInScopeNodes total number of nodes under parentNode, excluding
* the excludedScopeNode
* @param availableNodes number of available nodes under parentNode that
* could be chosen, excluding excludedNodes
* @return the chosen node, or null if none can be chosen
*/
private Node chooseRandom(final InnerNode parentNode,
final Node excludedScopeNode, final Collection<Node> excludedNodes,
final int totalInScopeNodes, final int availableNodes) {
Preconditions.checkArgument(
totalInScopeNodes >= availableNodes && availableNodes > 0, String
.format("%d should >= %d, and both should be positive.",
totalInScopeNodes, availableNodes));
if (excludedNodes == null || excludedNodes.isEmpty()) {
// if there are no excludedNodes, randomly choose a node
final int index = r.nextInt(totalInScopeNodes);
return parentNode.getLeaf(index, excludedScopeNode);
}
// excludedNodes non empty.
// Choose the nth VALID node, where n is random. VALID meaning it can be
// returned, after considering exclude scope and exclude nodes.
// The probability of being chosen should be equal for all VALID nodes.
// Notably, we do NOT choose nth node, and find the next valid node
// if n is excluded - this will make the probability of the node immediately
// after an excluded node higher.
//
// Start point is always 0 and that's fine, because the nth valid node
// logic provides equal randomness.
//
// Consider this example, where 1,3,5 out of the 10 nodes are excluded:
// 1 2 3 4 5 6 7 8 9 10
// x x x
// We will randomly choose the nth valid node where n is [0,6].
// We do NOT choose a random number n and just use the closest valid node,
// for example both n=3 and n=4 will choose 4, making it a 2/10 probability,
// higher than the expected 1/7
// totalInScopeNodes=10 and availableNodes=7 in this example.
int nthValidToReturn = r.nextInt(availableNodes);
LOG.debug("nthValidToReturn is {}", nthValidToReturn);
Node ret =
parentNode.getLeaf(r.nextInt(totalInScopeNodes), excludedScopeNode);
if (!excludedNodes.contains(ret)) {
// return if we're lucky enough to get a valid node at a random first pick
LOG.debug("Chosen node {} from first random", ret);
return ret;
} else {
ret = null;
}
Node lastValidNode = null;
for (int i = 0; i < totalInScopeNodes; ++i) {
ret = parentNode.getLeaf(i, excludedScopeNode);
if (!excludedNodes.contains(ret)) {
if (nthValidToReturn == 0) {
break;
}
--nthValidToReturn;
lastValidNode = ret;
} else {
LOG.debug("Node {} is excluded, continuing.", ret);
ret = null;
}
}
if (ret == null && lastValidNode != null) {
LOG.error("BUG: Found lastValidNode {} but not nth valid node. "
+ "parentNode={}, excludedScopeNode={}, excludedNodes={}, "
+ "totalInScopeNodes={}, availableNodes={}, nthValidToReturn={}.",
lastValidNode, parentNode, excludedScopeNode, excludedNodes,
totalInScopeNodes, availableNodes, nthValidToReturn);
ret = lastValidNode;
}
return ret;
}
/** return leaves in <i>scope</i>
* @param scope a path string
* @return leaves nodes under specific scope

75
hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/net/TestNetworkTopology.java
View File

@ -27,10 +27,9 @@
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Random;
import java.util.Set;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hdfs.DFSTestUtil;
import org.apache.hadoop.hdfs.HdfsConfiguration;
@ -39,14 +38,19 @@
import org.apache.hadoop.hdfs.protocol.HdfsConstants.DatanodeReportType;
import org.apache.hadoop.hdfs.server.blockmanagement.DatanodeDescriptor;
import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocols;
import org.apache.hadoop.test.GenericTestUtils;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.Timeout;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.event.Level;
public class TestNetworkTopology {
private static final Log LOG = LogFactory.getLog(TestNetworkTopology.class);
private static final Logger LOG =
LoggerFactory.getLogger(TestNetworkTopology.class);
private final static NetworkTopology cluster =
NetworkTopology.getInstance(new Configuration());
private DatanodeDescriptor dataNodes[];
@ -83,6 +87,7 @@ public void setupDatanodes() {
}
dataNodes[9].setDecommissioned();
dataNodes[10].setDecommissioned();
GenericTestUtils.setLogLevel(NetworkTopology.LOG, Level.TRACE);
}
@Test
@ -324,6 +329,7 @@ private Map<Node, Integer> pickNodesAtRandom(int numNodes,
frequency.put(random, frequency.get(random) + 1);
}
}
LOG.info("Result:" + frequency);
return frequency;
}
@ -471,4 +477,67 @@ public void testInvalidNetworkTopologiesNotCachedInHdfs() throws Exception {
}
}
/**
* Tests chooseRandom with include scope, excluding a few nodes.
*/
@Test
public void testChooseRandomInclude1() {
final String scope = "/d1";
final Set<Node> excludedNodes = new HashSet<>();
final Random r = new Random();
for (int i = 0; i < 4; ++i) {
final int index = r.nextInt(5);
excludedNodes.add(dataNodes[index]);
}
Map<Node, Integer> frequency = pickNodesAtRandom(100, scope, excludedNodes);
verifyResults(5, excludedNodes, frequency);
}
/**
* Tests chooseRandom with include scope at rack, excluding a node.
*/
@Test
public void testChooseRandomInclude2() {
String scope = dataNodes[0].getNetworkLocation();
Set<Node> excludedNodes = new HashSet<>();
final Random r = new Random();
int index = r.nextInt(1);
excludedNodes.add(dataNodes[index]);
final int count = 100;
Map<Node, Integer> frequency =
pickNodesAtRandom(count, scope, excludedNodes);
verifyResults(1, excludedNodes, frequency);
}
private void verifyResults(int upperbound, Set<Node> excludedNodes,
Map<Node, Integer> frequency) {
LOG.info("Excluded nodes are: {}", excludedNodes);
for (int i = 0; i < upperbound; ++i) {
final Node n = dataNodes[i];
LOG.info("Verifying node {}", n);
if (excludedNodes.contains(n)) {
assertEquals(n + " should not have been chosen.", 0,
(int) frequency.get(n));
} else {
assertTrue(n + " should have been chosen", frequency.get(n) > 0);
}
}
}
/**
* Tests chooseRandom with include scope, no exlucde nodes.
*/
@Test
public void testChooseRandomInclude3() {
String scope = "/d1";
Map<Node, Integer> frequency = pickNodesAtRandom(200, scope, null);
LOG.info("No node is excluded.");
for (int i = 0; i < 5; ++i) {
// all nodes should be more than zero
assertTrue(dataNodes[i] + " should have been chosen.",
frequency.get(dataNodes[i]) > 0);
}
}
}