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https://issues.apache.org/jira/browse/HDFS-9361?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Wei-Chiu Chuang resolved HDFS-9361.
-----------------------------------
Resolution: Not A Problem
I spent some time discussing the issue with [~walter.k.su] and I also agree
this is not a problem. The test can be configured to ignore load factor.
> Default block placement policy causes TestReplaceDataNodeOnFailure to fail
> intermittently
> -----------------------------------------------------------------------------------------
>
> Key: HDFS-9361
> URL: https://issues.apache.org/jira/browse/HDFS-9361
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: HDFS
> Reporter: Wei-Chiu Chuang
>
> TestReplaceDatanodeOnFailure sometimes fail (See HDFS-6101).
> (For background information, the test case set up a cluster with three data
> nodes, add two more data nodes, remove one data nodes, and verify that
> clients can correctly recover from the failure and set up three replicas)
> I traced down and found that some times a client only set up a pipeline with
> only two data nodes, which is one less than configured in the test case, even
> though the test case configures to always replace failed nodes.
> Digging into the log, I saw:
> {noformat}
> 2015-11-02 12:07:38,634 [IPC Server handler 8 on 50673] WARN
> blockmanagement.BlockPlacementPolicy
> (BlockPlacementPolicyDefault.java:chooseTarget(355)) - Failed to place enough
> replicas, still in nee
> d of 1 to reach 3 (unavailableStorages=[],
> storagePolicy=BlockStoragePolicy{HOT:7, storageTypes=[DISK],
> creationFallbacks=[], replicationFallbacks=[ARCHIVE]}, newBlock=true)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy$NotEnoughReplicasException:
> [
> Node /rack0/127.0.0.1:32931 [
> Datanode 127.0.0.1:32931 is not chosen since the rack has too many chosen
> nodes .
> ]
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseRandom(BlockPlacementPolicyDefault.java:723)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseRemoteRack(BlockPlacementPolicyDefault.java:624)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTargetInOrder(BlockPlacementPolicyDefault.java:429)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:342)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:220)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:105)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:120)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget4NewBlock(BlockManager.java:1727)
> at
> org.apache.hadoop.hdfs.server.namenode.FSDirWriteFileOp.chooseTargetForNewBlock(FSDirWriteFileOp.java:299)
> at
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2457)
> at
> org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:796)
> at
> org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:500)
> at
> org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
> at
> org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:637)
> at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:976)
> at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2305)
> at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2301)
> at java.security.AccessController.doPrivileged(Native Method)
> at javax.security.auth.Subject.doAs(Subject.java:415)
> at
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1669)
> at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2299)
> {noformat}
> So from the log, it seems the policy causes the pipeline selection to give up
> on the data node.
> I wonder whether this is appropriate or not. If the load factor exceeds
> certain threshold, but the file is insufficient of replicas, should it accept
> it as is, or should it attempt to acquire more replicas?
> I am filing this JIRA for discussion. I am very unfamiliar with block
> placement, so I may be wrong about my hypothesis.
> (Edit: I turned on DEBUG option for Log4j, and changed the logging message a
> bit to make it show the stack trace)
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