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https://issues.apache.org/jira/browse/HDFS-7661?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15152326#comment-15152326
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GAO Rui commented on HDFS-7661:
-------------------------------
I am running into trouble when trying to overwrite and roll by data file file
channel position by directly operate on underlying {{RandomAccessFile}} of data
file {{OutputStream}} in {{BlockReceiver#receivePacket()}} just like what we
are doing for overwrite checksum file.
I was planing to truncate both the overwritten data in the end of both data
file and .meta file in parity datanode, then store the overwritten data in the
end of .meta file. One possible way to keep the data before first flush safe
even if the second flush fails, maybe we could add {{upgrade/rollback}}
mechanism of {{DataStorage}} alike method to data/checksum file of parity
datanodes.
I will try to address the {{RandomAccessFile}} issue and attach this wip patch
ASAP.
> Erasure coding: support hflush and hsync
> ----------------------------------------
>
> Key: HDFS-7661
> URL: https://issues.apache.org/jira/browse/HDFS-7661
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Tsz Wo Nicholas Sze
> Assignee: GAO Rui
> Attachments: EC-file-flush-and-sync-steps-plan-2015-12-01.png,
> HDFS-7661-unitTest-wip-trunk.patch,
> HDFS-EC-file-flush-sync-design-version1.1.pdf,
> HDFS-EC-file-flush-sync-design-version2.0.pdf
>
>
> We also need to support hflush/hsync and visible length.
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