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https://issues.apache.org/jira/browse/HDFS-8763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14624303#comment-14624303
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jiangyu commented on HDFS-8763:
-------------------------------
Hi, [~walter.k.su] , that is true, most of the blocks are very small, but i
also found some blocks can be MB in this situation. That is very dangerous
when you make fail over of namenode , which excess block can not delete until
namenode think the datanodes are not stale. I found this when i investigation
this jira https://issues.apache.org/jira/browse/HDFS-6425.
> Incremental blockreport order may replicate unnecessary block
> -------------------------------------------------------------
>
> 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
> Priority: Minor
>
> 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:
> 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]
> 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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