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https://issues.apache.org/jira/browse/HDFS-5182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13891500#comment-13891500
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Colin Patrick McCabe commented on HDFS-5182:
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bq. I should have said it more concretely. What I'm proposing is that the DN
passes the file descriptor to the client (e.g., using ioctl() in Linux).
Did you read my first comment? It begins:
bq. One way (let's call this choice #1) was using a shared memory segment. This
would take the form of a third file descriptor passed from the DataNode to the
DFSClient
By the way, {{ioctl}} cannot be used to pass file descriptors in Linux.
> BlockReaderLocal must allow zero-copy reads only when the DN believes it's
> valid
> ---------------------------------------------------------------------------------
>
> Key: HDFS-5182
> URL: https://issues.apache.org/jira/browse/HDFS-5182
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 3.0.0
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
>
> BlockReaderLocal must allow zero-copy reads only when the DN believes it's
> valid. This implies adding a new field to the response to
> REQUEST_SHORT_CIRCUIT_FDS. We also need some kind of heartbeat from the
> client to the DN, so that the DN can inform the client when the mapped region
> is no longer locked into memory.
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