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https://issues.apache.org/jira/browse/HDFS-14181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16731583#comment-16731583
]
Ayush Saxena commented on HDFS-14181:
-------------------------------------
Thanx [~sihai] for the patch.
I too agree with [~elgoiri] that we should implement the correct way.
I tried digging into the problem.
Thats something what I understood of the scenario.Let me Know If I get it wrong
somewhere.
Let the setup be like ::
(Cluster Map)
1 2 3 4 5 6 7 8 9 10
1-8 is scope
1-4 is excluded scope
2 and 7 is excluded node
* *Present Scenario ::*
Avlbl node (Present)--> 5,6,8,9,10 (5)
_{Cluster Map - Excluded Scope and Excluded nodes out of Excluded Scope} \{ 10
- 4 - 1 = 5}_
Avlbl node (Expected) ---> 5,6,8 (*3*)
_{Scope - Exclude Scope - Excluded nodes out of Excluded Scope but in scope }_
{ 8 - 4 - 1 = 3}
* *Proposed Solution ::*
Part1 --> 1,3,4,5,6,8 (6)
_{Scope - Excluded Nodes in scope}_
Part2 --> 1,3,4 (3)
_{Excluded Scope - Excluded Nodes in Excluded Scope }_
*Solution Received* =
{ Part1 - Part2 }
6-3 = *3* (*Correct*)
By my understanding the solution seems correct. :)
Just I guess If we are expecting this method to be called from somewhere else
too.We can add a NULL check for scope too in the else part for safety as before
scope wasn't being used in the block. Secondly Am not very sure regarding
taking the read Lock.
> 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
> Priority: Major
> Attachments: 0001-add-UT-for-NetworkTopology.patch,
> 0001-fix-NetworkTopology.java-chooseRandom-bug.patch, HDFS-14181.01.patch,
> HDFS-14181.02.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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