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https://issues.apache.org/jira/browse/HDFS-7979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14378415#comment-14378415
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Colin Patrick McCabe commented on HDFS-7979:
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I am not sure about this patch for a few reasons:
* When using the monotonic time, two block reports cannot get the same ID since
the monotonic time is always increasing. We don't have the same guarantee
here. Admittedly, the chances of a repeat are extremely low. But previously
they were effectively 0, and now they're nonzero.
* If the datanode is taken down and restarted, the monotonic time will still be
higher than before. And so the current behavior makes it easy to see from the
logs that block report N+1 came after block report N, even if there was a
datanode restart in between. We don't have this behavior with a random number
generated on datanode start.
I also don't think a non-random block report ID is a security concern. If
block reports need to be secured, the correct way to do it is to use
encryption-over-the-wire via SASL. If SASL is not in use, any evildoer can
submit a fake full block report that says that everything is deleted, or talk
about bogus blocks that don't really exist on the datanode. Indeed, even after
this patch is applied, it would be easy for a black hat to submit a new block
report with a new random ID and cause the NN to delete all the storages on that
DN. So essentially the motivation for this patch is not valid in my opinion.
> Initialize block report IDs with a random number
> ------------------------------------------------
>
> Key: HDFS-7979
> URL: https://issues.apache.org/jira/browse/HDFS-7979
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 2.7.0
> Reporter: Andrew Wang
> Assignee: Andrew Wang
> Priority: Minor
> Attachments: HDFS-7979.001.patch
>
>
> Right now block report IDs use system nanotime. This isn't that random, so
> let's start it at a random number for some more safety.
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