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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1262) Failed pipeline creation during append leaves lease hanging on NN
Date Thu, 24 Jun 2010 14:00:51 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12882160#action_12882160
] 

Todd Lipcon commented on HDFS-1262:
-----------------------------------

Oof, what a hack that would be :) Not to say we shouldn't do that over in HBase in the short
term, but I agree let's treat this as a serious bug in 0.20-append and try to fix it on the
HDFS side unless we really can't think of any implementable solutions.

Can you think of a problem with the abandonBlock() solution? My thinking is that we'd check
if the block is the last block of a file under construction by the abandoning client, and
if so, reassign lease to NN_Recovery and initiate block synchronization from the NN as if
the lease were lost. It may not be necessary to go through the whole recovery process, but
it will be safer in case the client half set up a pipeline before failing, or somesuch.

> 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
>            Priority: Critical
>             Fix For: 0.20-append
>
>
> 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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