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https://issues.apache.org/jira/browse/HDFS-3161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13248247#comment-13248247
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Uma Maheswara Rao G commented on HDFS-3161:
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Yes, I am seeing many issues related 20-Append, all are mainly due to recovery.
I agree with you (also i have seen many times you have pointed it), since
append is working pretty well in latest releases than 20-append, we can disable
it.
Since we are dropping support for 20 append issues, it is better, we can
officially announce?
Some customers have started using this append unknowingly.
> 20 Append: Excluded DN replica from recovery should be removed from DN.
> -----------------------------------------------------------------------
>
> Key: HDFS-3161
> URL: https://issues.apache.org/jira/browse/HDFS-3161
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 1.0.0
> Reporter: suja s
> Priority: Critical
> Fix For: 1.0.3
>
>
> 1) DN1->DN2->DN3 are in pipeline.
> 2) Client killed abruptly
> 3) one DN has restarted , say DN3
> 4) In DN3 info.wasRecoveredOnStartup() will be true
> 5) NN recovery triggered, DN3 skipped from recovery due to above check.
> 6) Now DN1, DN2 has blocks with generataion stamp 2 and DN3 has older
> generation stamp say 1 and also DN3 still has this block entry in
> ongoingCreates
> 7) as part of recovery file has closed and got only two live replicas ( from
> DN1 and DN2)
> 8) So, NN issued the command for replication. Now DN3 also has the replica
> with newer generation stamp.
> 9) Now DN3 contains 2 replicas on disk. and one entry in ongoing creates with
> referring to blocksBeingWritten directory.
> When we call append/ leaseRecovery, it may again skip this node for that
> recovery as blockId entry still presents in ongoingCreates with startup
> recovery true.
> It may keep continue this dance for evry recovery.
> And this stale replica will not be cleaned untill we restart the cluster.
> Actual replica will be trasferred to this node only through replication
> process.
> Also unnecessarily that replicated blocks will get invalidated after next
> recoveries....
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