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https://issues.apache.org/jira/browse/HDFS-3960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13487060#comment-13487060
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Aaron T. Myers commented on HDFS-3960:
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bq. The document proposes to add new functionality as far as I understand. I
just propose to add a parameter to fsync(). Because sync can and should adjust
file length, just like close. The client is the only authority that knows the
exact file length.
I think we're agreeing here, just using different terms. The document is
presently discussing how the DFSOutputStream API would be changed to add an
optional parameter to hflush() and hsync() which would cause the client to
update the length on the NN. What you're describing is how that would be
implemented: by changing the ClientProtocol#fsync method to also take a length
parameter. I'll update the document to make this clear.
bq. I don't think files that were not hflush-ed should be excluded from
snapshots as the document proposes. Everything should be versioned.
That would be fine too. Excluding them seemed simpler, but I don't feel
strongly about it. The length of that file in the snapshot would then be at the
last block boundary before the snapshot was taken. I'll update the design
document to reflect that.
Thanks a lot for the comments, Konstantin, and for taking a look at the doc.
Your feedback is very valuable.
> Snapshot of Being Written Files
> -------------------------------
>
> Key: HDFS-3960
> URL: https://issues.apache.org/jira/browse/HDFS-3960
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
>
> Here is a design question: Suppose there is a being written file when a
> snapshot is being taken. What should the length of the file be shown in the
> snapshot? In other words, how to determine the length of being written file
> when a snapshot is being taken?
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