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https://issues.apache.org/jira/browse/HDFS-4660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13627388#comment-13627388
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PengZhang commented on HDFS-4660:
---------------------------------
The scenario for this issue is simple: client send a packet, part of which
needs to write and part needs to skip. When amount of data to skip reaches
trunk size, receiver doesn't skip checksum and has it duplicated.
But for unit test, I found receivePacket() got many dependences and there's no
test for it before. So I think it's not easy to add unit tests for it.
Any good ideas, Todd?
> Duplicated checksum on DN in a recovered pipeline
> -------------------------------------------------
>
> Key: HDFS-4660
> URL: https://issues.apache.org/jira/browse/HDFS-4660
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 3.0.0, 2.0.3-alpha
> Reporter: PengZhang
> Priority: Critical
> Attachments: HDFS-4660.patch
>
>
> pipeline DN1 DN2 DN3
> stop DN2
> pipeline added node DN4 located at 2nd position
> DN1 DN4 DN3
> recover RBW
> DN4 after recover rbw
> 2013-04-01 21:02:31,570 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Recover
> RBW replica
> BP-325305253-10.2.201.14-1364820083462:blk_-9076133543772600337_1004
> 2013-04-01 21:02:31,570 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl:
> Recovering ReplicaBeingWritten, blk_-9076133543772600337_1004, RBW
> getNumBytes() = 134144
> getBytesOnDisk() = 134144
> getVisibleLength()= 134144
> end at chunk (134144/512=262)
> DN3 after recover rbw
> 2013-04-01 21:02:31,575 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Recover
> RBW replica
> BP-325305253-10.2.201.14-1364820083462:blk_-9076133543772600337_10042013-04-01
> 21:02:31,575 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl:
> Recovering ReplicaBeingWritten, blk_-9076133543772600337_1004, RBW
> getNumBytes() = 134028
> getBytesOnDisk() = 134028
> getVisibleLength()= 134028
> client send packet after recover pipeline
> offset=133632 len=1008
> DN4 after flush
> 2013-04-01 21:02:31,779 DEBUG
> org.apache.hadoop.hdfs.server.datanode.DataNode: FlushOrsync, file
> offset:134640; meta offset:1063
> // meta end position should be floor(134640/512)*4 + 7 == 1059, but now it is
> 1063.
> DN3 after flush
> 2013-04-01 21:02:31,782 DEBUG
> org.apache.hadoop.hdfs.server.datanode.DataNode: PacketResponder:
> BP-325305253-10.2.201.14-1364820083462:blk_-9076133543772600337_1005,
> type=LAST_IN_PIPELINE, downstreams=0:[]: enqueue Packet(seqno=219,
> lastPacketInBlock=false, offsetInBlock=134640,
> ackEnqueueNanoTime=8817026136871545)
> 2013-04-01 21:02:31,782 DEBUG
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Changing
> meta file offset of block
> BP-325305253-10.2.201.14-1364820083462:blk_-9076133543772600337_1005 from
> 1055 to 1051
> 2013-04-01 21:02:31,782 DEBUG
> org.apache.hadoop.hdfs.server.datanode.DataNode: FlushOrsync, file
> offset:134640; meta offset:1059
> After checking meta on DN4, I found checksum of chunk 262 is duplicated, but
> data not.
> Later after block was finalized, DN4's scanner detected bad block, and then
> reported it to NM. NM send a command to delete this block, and replicate this
> block from other DN in pipeline to satisfy duplication num.
> I think this is because in BlockReceiver it skips data bytes already written,
> but not skips checksum bytes already written. And function
> adjustCrcFilePosition is only used for last non-completed chunk, but
> not for this situation.
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