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https://issues.apache.org/jira/browse/HDFS-14181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16731763#comment-16731763
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Sihai Ke edited comment on HDFS-14181 at 1/2/19 4:50 AM:
---------------------------------------------------------
[~hexiaoqiao] [~elgoiri] [~ayushtkn] thanks for comments, I think the read
lock is needed, below is my thought.
# we want to count node number under in scope, but not in excludeScope. assume
the excludedNodes is null. then we call
availableNodes = countNumOfAvailableNodes(scope, excludedNodes) -
countNumOfAvailableNodes(excludedScope, excludedNodes);
we could split it to two steps:
step 1: countNumOfAvailableNodes(scope, excludedNodes); // num
under scope
step 2: countNumOfAvailableNodes(excludedScope, excludedNodes); // num under
excludedScope.
# if we don't add lock for step1 and step2, after step1, if more nodes are
added to excludeScope, we will find step2 result is larger than step1, which
shouldn't happen.
# In order to trigger the bug that caused of no read lock, I upload a patch
HDFS-14181.04.patch. which will be discarded in the futhre.
currently: HDFS-14181.03.patch is the solution that I proposed, and
HDFS-14181.04.patch is the code change that approve lock is needed. and will be
discarded in the future.
was (Author: sihai):
[~hexiaoqiao] [~elgoiri] [~ayushtkn] thanks for comments, I think the read
lock is needed, below is my thought.
# we want to count node number under in scope, but not in excludeScope. assume
the excludedNodes is null. then we call
availableNodes = countNumOfAvailableNodes(scope, excludedNodes) -
countNumOfAvailableNodes(excludedScope, excludedNodes);
we could split it to two steps:
step 1: countNumOfAvailableNodes(scope, excludedNodes); // num
under scope
step 2: countNumOfAvailableNodes(excludedScope, excludedNodes); // num under
excludedScope.
# if we don't add lock for step1 and step2, after step1, if more nodes are
added to excludeScope, we will find step2 result is larger than step1, which
shouldn't happen.
# In order to trigger the bug that caused of no read lock, I upload a patch
HDFS-14181.04.patch. which will be discarded in the futhre.
> Suspect there is a bug in NetworkTopology.java chooseRandom function.
> ---------------------------------------------------------------------
>
> Key: HDFS-14181
> URL: https://issues.apache.org/jira/browse/HDFS-14181
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs, namenode
> Affects Versions: 2.9.2
> Reporter: Sihai Ke
> Assignee: Sihai Ke
> Priority: Major
> Attachments: 0001-add-UT-for-NetworkTopology.patch,
> 0001-fix-NetworkTopology.java-chooseRandom-bug.patch, HDFS-14181.01.patch,
> HDFS-14181.02.patch, HDFS-14181.03.patch, HDFS-14181.04.patch,
> image-2018-12-29-15-02-19-415.png
>
>
> During reading the hadoop NetworkTopology.java, I suspect there is a bug in
> function
> chooseRandom (line 498, hadoop version 2.9.2-RC0),
> I think there is a bug in{color:#f79232} code, ~excludedScope doesn't mean
> availableNodes under Scope node, and I also add unit test for this and get an
> exception.{color}
> bug code in the else.
> {code:java}
> // code placeholder
> if (excludedScope == null) {
> availableNodes = countNumOfAvailableNodes(scope, excludedNodes);
> } else {
> availableNodes =
> countNumOfAvailableNodes("~" + excludedScope, excludedNodes);
> }{code}
> Source code:
> {code:java}
> // code placeholder
> protected Node chooseRandom(final String scope, String excludedScope,
> final Collection<Node> excludedNodes) {
> if (excludedScope != null) {
> if (scope.startsWith(excludedScope)) {
> return null;
> }
> if (!excludedScope.startsWith(scope)) {
> excludedScope = null;
> }
> }
> Node node = getNode(scope);
> if (!(node instanceof InnerNode)) {
> return excludedNodes != null && excludedNodes.contains(node) ?
> null : node;
> }
> InnerNode innerNode = (InnerNode)node;
> int numOfDatanodes = innerNode.getNumOfLeaves();
> if (excludedScope == null) {
> node = null;
> } else {
> node = getNode(excludedScope);
> if (!(node instanceof InnerNode)) {
> numOfDatanodes -= 1;
> } else {
> numOfDatanodes -= ((InnerNode)node).getNumOfLeaves();
> }
> }
> if (numOfDatanodes <= 0) {
> LOG.debug("Failed to find datanode (scope=\"{}\" excludedScope=\"{}\")."
> + " numOfDatanodes={}",
> scope, excludedScope, numOfDatanodes);
> return null;
> }
> final int availableNodes;
> if (excludedScope == null) {
> availableNodes = countNumOfAvailableNodes(scope, excludedNodes);
> } else {
> availableNodes =
> countNumOfAvailableNodes("~" + excludedScope, excludedNodes);
> }
> LOG.debug("Choosing random from {} available nodes on node {},"
> + " scope={}, excludedScope={}, excludeNodes={}. numOfDatanodes={}.",
> availableNodes, innerNode, scope, excludedScope, excludedNodes,
> numOfDatanodes);
> Node ret = null;
> if (availableNodes > 0) {
> ret = chooseRandom(innerNode, node, excludedNodes, numOfDatanodes,
> availableNodes);
> }
> LOG.debug("chooseRandom returning {}", ret);
> return ret;
> }
> {code}
>
>
> Add Unit Test in TestClusterTopology.java, but get exception.
>
> {code:java}
> // code placeholder
> @Test
> public void testChooseRandom1() {
> // create the topology
> NetworkTopology cluster = NetworkTopology.getInstance(new Configuration());
> NodeElement node1 = getNewNode("node1", "/a1/b1/c1");
> cluster.add(node1);
> NodeElement node2 = getNewNode("node2", "/a1/b1/c1");
> cluster.add(node2);
> NodeElement node3 = getNewNode("node3", "/a1/b1/c2");
> cluster.add(node3);
> NodeElement node4 = getNewNode("node4", "/a1/b2/c3");
> cluster.add(node4);
> Node node = cluster.chooseRandom("/a1/b1", "/a1/b1/c1", null);
> assertSame(node.getName(), "node3");
> }
> {code}
>
> Exception:
> {code:java}
> // code placeholder
> java.lang.IllegalArgumentException: 1 should >= 2, and both should be
> positive.
> at com.google.common.base.Preconditions.checkArgument(Preconditions.java:88)
> at
> org.apache.hadoop.net.NetworkTopology.chooseRandom(NetworkTopology.java:567)
> at
> org.apache.hadoop.net.NetworkTopology.chooseRandom(NetworkTopology.java:544)
> atorg.apache.hadoop.net.TestClusterTopology.testChooseRandom1(TestClusterTopology.java:198)
> {code}
>
> {color:#f79232}!image-2018-12-29-15-02-19-415.png!{color}
>
>
> [~vagarychen] this change is imported in PR HDFS-11577, could you help to
> check whether this is a bug ?
>
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