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https://issues.apache.org/jira/browse/HDFS-4089?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13480422#comment-13480422
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Todd Lipcon commented on HDFS-4089:
-----------------------------------
Hi Jan. The purpose of this flag isn't for data integrity -- it's to avoid
lumpy IO writeback. If you want data integrity you should be using the hsync()
call after every write.
> SyncBehindWrites uses wrong flags on sync_file_range
> ----------------------------------------------------
>
> Key: HDFS-4089
> URL: https://issues.apache.org/jira/browse/HDFS-4089
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: data-node, ha
> Reporter: Jan Kunigk
> Priority: Minor
> Attachments: syncBehindWrites.patch
>
>
> Hi, I stumbled upon this while trying to understand the append design
> recently. I am assuming when SyncBehindWrites is enabled we do indeed want to
> do a complete sync after each write. In that case the implementation seems
> wrong to me.
> Here's a comment from the manpage of sync_file_range on the usage of the
> SYNC_FILE_RANGE_WRITE flag in solitude: "This is an asynchronous
> flush-to-disk operation. This is not suitable for data integrity operations."
> I don't know why this syscall is invoked here instead of just fsync
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