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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10301) BlockReport retransmissions may lead to storages falsely being declared zombie if storage report processing happens out of order
Date Wed, 25 May 2016 01:48:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15299313#comment-15299313
] 

Konstantin Shvachko commented on HDFS-10301:
--------------------------------------------

Hey Colin, let's decide on the way to move forward. I do not see a point in making this change
in two steps.
* Your changes will essentially be completely removed by Vinitha's patch.
* I do not see her patch introducing incompatible changes. So it can and should be backported
through to branch 2.6.

A thorough review is needed and will be quite helpful. I think the [004 patch|https://issues.apache.org/jira/secure/attachment/12805798/HDFS-10301.004.patch]
covers 
* the upgrade case, that is, it works consistently for both old (pre-patch) and new (patched)
DataNodes block reports
* the case when the entire block report is sent in a single RPC and
* the case when block reports are split into multiple RPCs
* the leases

So apart from the failed test I do not see any issues. It would be good if you could take
a fresh look, see if any corner cases were missed.

> BlockReport retransmissions may lead to storages falsely being declared zombie if storage
report processing happens out of order
> --------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-10301
>                 URL: https://issues.apache.org/jira/browse/HDFS-10301
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.6.1
>            Reporter: Konstantin Shvachko
>            Assignee: Colin Patrick McCabe
>            Priority: Critical
>         Attachments: HDFS-10301.002.patch, HDFS-10301.003.patch, HDFS-10301.004.patch,
HDFS-10301.005.patch, HDFS-10301.01.patch, HDFS-10301.sample.patch, zombieStorageLogs.rtf
>
>
> When NameNode is busy a DataNode can timeout sending a block report. Then it sends the
block report again. Then NameNode while process these two reports at the same time can interleave
processing storages from different reports. This screws up the blockReportId field, which
makes NameNode think that some storages are zombie. Replicas from zombie storages are immediately
removed, causing missing blocks.



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