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https://issues.apache.org/jira/browse/HDFS-4089?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13484557#comment-13484557
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Jan Kunigk commented on HDFS-4089:
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Hi Todd, sorry the lag in my replies. I think we can improve the naming at
least.
1) I would rename the variable from SyncBehindWrites to WriteOutDirtyOSPages.
Sync is misleading, since, even though the syscall is named sync_file_range,
the flags that it is used with here do not entail sync semantics, i.e. a
synchronous, i.e. blocking operation.
2) I think we should mark the appropriate section in DFSConfigKeys.java as
"performance related"
This is more an issue of hygiene and, after your explanations, no longer a
concern w/r to data integrity. Thanks.
> 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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