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https://issues.apache.org/jira/browse/HDFS-10301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15313112#comment-15313112
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Zhe Zhang commented on HDFS-10301:
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Thanks for the discussions [~cmccabe], [~shv],[~redvine]
I think the challenge here is that different deployments have different levels
of 1) BR split; 2) BRs interleaving; 3) zombie storages. E.g. BR split might be
completely turned off in configuration, and BR interleaving heavily depends on
how busy the NN is.
*a)* Patch v5 (from Colin) works well when BRs rarely interleave. In the worst
case, a zombie storage could remain on NN for several full-BR cycles.
*b)* Patch v4 (from Vinitha) works well when BRs are rarely split (or split
into many RPCs). The worst case is where each BR is split into a small number
of RPCs -- if each full BR is split into {{n}} RPCs, the relative overhead is 1
/ n, in terms of # of RPCs.
*c)* As Colin suggested, we can also extend first / last RPC in a full BR with
the list of storages. By doing that we are adding overhead to every BR RPC (it
needs to mark whether it has the list). Theoretically, the worst-case-overhead
is to add this to an empty BR.
So overall, I think c) is the best long term solution, because its worst case
scenario is the least likely to happen, and the consequence is the most
tolerable. It is more complex than b) though. Given the size of the v4 patch,
are we OK to go with b) (v4 patch) first and do c) as a follow-on?
> 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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