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https://issues.apache.org/jira/browse/HDFS-1965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13036531#comment-13036531
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Todd Lipcon commented on HDFS-1965:
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I can think of a couple possible solutions:
a) make the methods that operate on a block take an additional parameter to
contain block tokens, rather than using the normal token selector mechanism
that scopes credentials on a per-connection basis. This has the advantage that
we can even re-use an IPC connection across different blocks.
b) when the client creates an IPC proxy to a DN, it can explicitly configure
the maxIdleTime to 0 so that we don't leave connections hanging around after
the call completes. This is less efficient than option A above, but it probably
doesn't matter much for this use case.
> IPCs done using block token-based tickets can't reuse connections
> -----------------------------------------------------------------
>
> Key: HDFS-1965
> URL: https://issues.apache.org/jira/browse/HDFS-1965
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: security
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Critical
> Fix For: 0.22.0
>
>
> This is the reason that TestFileConcurrentReaders has been failing a lot.
> Reproducing a comment from HDFS-1057:
> The test has a thread which continually re-opens the file which is being
> written to. Since the file's in the middle of being written, it makes an RPC
> to the DataNode in order to determine the visible length of the file. This
> RPC is authenticated using the block token which came back in the
> LocatedBlocks object as the security ticket.
> When this RPC hits the IPC layer, it looks at its existing connections and
> sees none that can be re-used, since the block token differs between the two
> requesters. Hence, it reconnects, and we end up with hundreds or thousands of
> IPC connections to the datanode.
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