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https://issues.apache.org/jira/browse/HDFS-1262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901268#action_12901268
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Todd Lipcon commented on HDFS-1262:
-----------------------------------
re RPC compatibility - I agree it's not a requirement on trunk, but so far
we've kept branch-20-append compatible with a "your mileage may vary since we
haven't tested the compatibility matrix". If it's too complicated to do a
fallback code path that maintains the current buggy behavior, that's OK.
> Failed pipeline creation during append leaves lease hanging on NN
> -----------------------------------------------------------------
>
> Key: HDFS-1262
> URL: https://issues.apache.org/jira/browse/HDFS-1262
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs client, name-node
> Affects Versions: 0.20-append
> Reporter: Todd Lipcon
> Assignee: sam rash
> Priority: Critical
> Fix For: 0.20-append
>
> Attachments: hdfs-1262-1.txt, hdfs-1262-2.txt, hdfs-1262-3.txt,
> hdfs-1262-4.txt, hdfs-1262-5.txt
>
>
> Ryan Rawson came upon this nasty bug in HBase cluster testing. What happened
> was the following:
> 1) File's original writer died
> 2) Recovery client tried to open file for append - looped for a minute or so
> until soft lease expired, then append call initiated recovery
> 3) Recovery completed successfully
> 4) Recovery client calls append again, which succeeds on the NN
> 5) For some reason, the block recovery that happens at the start of append
> pipeline creation failed on all datanodes 6 times, causing the append() call
> to throw an exception back to HBase master. HBase assumed the file wasn't
> open and put it back on a queue to try later
> 6) Some time later, it tried append again, but the lease was still assigned
> to the same DFS client, so it wasn't able to recover.
> The recovery failure in step 5 is a separate issue, but the problem for this
> JIRA is that the NN can think it failed to open a file for append when the NN
> thinks the writer holds a lease. Since the writer keeps renewing its lease,
> recovery never happens, and no one can open or recover the file until the DFS
> client shuts down.
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