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https://issues.apache.org/jira/browse/HDFS-8763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14725709#comment-14725709
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Jitendra Nath Pandey commented on HDFS-8763:
--------------------------------------------
[~jingzhao] raised a very valid point that when the client closes a file it has
already received acks from the datanodes for the last block, which has been
finalized at the datanodes. Namenode is also aware of the datanodes in the
pipeline, therefore namenode does not really need to wait for {{blockReceived}}
messages and can complete the file. I think that would be a very useful
optimization. Additional advantage is that datanodes can lazily send
blockReceived message for newly finalized blocks and thus reduce load on
datanode-namenode traffic. I think we should take this discussion to a separate
jira.
> After file closed, a race condition between IBR of 3rd replica of lastBlock
> and ReplicationMonitor
> --------------------------------------------------------------------------------------------------
>
> Key: HDFS-8763
> URL: https://issues.apache.org/jira/browse/HDFS-8763
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: HDFS
> Affects Versions: 2.4.0
> Reporter: jiangyu
> Assignee: Walter Su
> Priority: Minor
> Attachments: HDFS-8763.01.patch
>
>
> -For our cluster, the NameNode is always very busy, so for every incremental
> block report , the contention of lock is heavy.-
> -The logic of incremental block report is as follow, client send block to dn1
> and dn1 mirror to dn2, dn2 mirror to dn3. After finish this block, all
> datanode will report the newly received block to namenode. In NameNode side,
> all will go to the method processIncrementalBlockReport in BlockManager
> class. But the status of the block reported from dn2,dn3 is RECEIVING_BLOCK,
> for dn1 is RECEIED_BLOCK. It is okay if dn2, dn3 report before dn1(that is
> common), but in some busy environment, it is easy to find dn1 report before
> dn2 or dn3, let’s assume dn2 report first, dn1 report second, and dn3 report
> third.-
> -So dn1 will addStoredBlock and find the replica of this block is not reach
> the the original number(which is 3), and the block will add to
> neededReplications construction and soon ask some node in pipeline (dn1 or
> dn2)to replica it dn4 . After sometime, dn4 and dn3 all report this block,
> then choose one node to invalidate.-
> Here is one log i found in our cluster:
> {noformat}
> 2015-07-08 01:05:34,675 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
> allocateBlock:
> /logs/***_bigdata_spam/logs/application_1435099124107_470749/xx.xx.4.62_45454.tmp.
> BP-1386326728-xx.xx.2.131-1382089338395
> blk_3194502674_2121080184{blockUCState=UNDER_CONSTRUCTION,
> primaryNodeIndex=-1,
> replicas=[ReplicaUnderConstruction[[DISK]DS-a7c0f8f6-2399-4980-9479-efa08487b7b3:NORMAL|RBW],
>
> ReplicaUnderConstruction[[DISK]DS-c75145a0-ed63-4180-87ee-d48ccaa647c5:NORMAL|RBW],
>
> ReplicaUnderConstruction[[DISK]DS-15a4dc8e-5b7d-449f-a941-6dced45e6f07:NORMAL|RBW]]}
> 2015-07-08 01:05:34,689 INFO BlockStateChange: BLOCK* addStoredBlock:
> blockMap updated: xx.xx.7.75:50010 is added to
> blk_3194502674_2121080184{blockUCState=UNDER_CONSTRUCTION,
> primaryNodeIndex=-1,
> replicas=[ReplicaUnderConstruction[[DISK]DS-15a4dc8e-5b7d-449f-a941-6dced45e6f07:NORMAL|RBW],
>
> ReplicaUnderConstruction[[DISK]DS-74ed264f-da43-4cc3-9fa9-164ba99f752a:NORMAL|RBW],
>
> ReplicaUnderConstruction[[DISK]DS-56121ce1-8991-45b3-95bc-2a5357991512:NORMAL|RBW]]}
> size 0
> 2015-07-08 01:05:34,689 INFO BlockStateChange: BLOCK* addStoredBlock:
> blockMap updated: xx.xx.4.62:50010 is added to
> blk_3194502674_2121080184{blockUCState=UNDER_CONSTRUCTION,
> primaryNodeIndex=-1,
> replicas=[ReplicaUnderConstruction[[DISK]DS-15a4dc8e-5b7d-449f-a941-6dced45e6f07:NORMAL|RBW],
>
> ReplicaUnderConstruction[[DISK]DS-74ed264f-da43-4cc3-9fa9-164ba99f752a:NORMAL|RBW],
>
> ReplicaUnderConstruction[[DISK]DS-56121ce1-8991-45b3-95bc-2a5357991512:NORMAL|RBW]]}
> size 0
> 2015-07-08 01:05:35,003 INFO BlockStateChange: BLOCK* ask xx.xx.4.62:50010 to
> replicate blk_3194502674_2121080184 to datanode(s) xx.xx.4.65:50010
> 2015-07-08 01:05:35,403 INFO BlockStateChange: BLOCK* addStoredBlock:
> blockMap updated: xx.xx.7.73:50010 is added to blk_3194502674_2121080184 size
> 67750
> 2015-07-08 01:05:35,833 INFO BlockStateChange: BLOCK* addStoredBlock:
> blockMap updated: xx.xx.4.65:50010 is added to blk_3194502674_2121080184 size
> 67750
> 2015-07-08 01:05:35,833 INFO BlockStateChange: BLOCK* InvalidateBlocks: add
> blk_3194502674_2121080184 to xx.xx.7.75:50010
> 2015-07-08 01:05:35,833 INFO BlockStateChange: BLOCK* chooseExcessReplicates:
> (xx.xx.7.75:50010, blk_3194502674_2121080184) is added to invalidated blocks
> set
> 2015-07-08 01:05:35,852 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
> InvalidateBlocks: ask xx.xx.7.75:50010 to delete [blk_3194502674_2121080184,
> blk_3194497594_2121075104]
> {noformat}
> Some day, the number of this situation can be 400000, that is not good for
> the performance and waste network band.
> Our base version is hadoop 2.4 and i have checked hadoop 2.7.1 didn’t find
> any difference.
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