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From "Hari Mankude (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2742) HA: observed dataloss in replication stress test
Date Thu, 12 Jan 2012 18:39:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13185133#comment-13185133
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Hari Mankude commented on HDFS-2742:
------------------------------------

This is a good idea. It keeps the log stream separate from the datanode based block msgs.
We would need to handle "lost" msgs. For example, primary might have received a block finalized
msg and the same msg was not delivered to standby. So, the block rbw msg on the standby queue
will have to be purged after a timeout.
                
> HA: observed dataloss in replication stress test
> ------------------------------------------------
>
>                 Key: HDFS-2742
>                 URL: https://issues.apache.org/jira/browse/HDFS-2742
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: data-node, ha, name-node
>    Affects Versions: HA branch (HDFS-1623)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Blocker
>         Attachments: hdfs-2742.txt, log-colorized.txt
>
>
> The replication stress test case failed over the weekend since one of the replicas went
missing. Still diagnosing the issue, but it seems like the chain of events was something like:
> - a block report was generated on one of the nodes while the block was being written
- thus the block report listed the block as RBW
> - when the standby replayed this queued message, it was replayed after the file was marked
complete. Thus it marked this replica as corrupt
> - it asked the DN holding the corrupt replica to delete it. And, I think, removed it
from the block map at this time.
> - That DN then did another block report before receiving the deletion. This caused it
to be re-added to the block map, since it was "FINALIZED" now.
> - Replication was lowered on the file, and it counted the above replica as non-corrupt,
and asked for the other replicas to be deleted.
> - All replicas were lost.

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