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https://issues.apache.org/jira/browse/HDFS-744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13016626#comment-13016626
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Hairong Kuang commented on HDFS-744:
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I thought more about this. It seems to me it is not easy to support hsync. If
the bytes written in between two hsync calls are across a block boundary. The
first block needs to get fsynced to disk as well.
An alternative proposal is to provide a filesystem create API that takes a
fsync option. If fsync is true, any hflush call will force the data to be
synced to disk and any block will be synced to disk upon close as well.
> Support hsync in HDFS
> ---------------------
>
> Key: HDFS-744
> URL: https://issues.apache.org/jira/browse/HDFS-744
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Hairong Kuang
>
> HDFS-731 implements hsync by default as hflush. As descriibed in HADOOP-6313,
> the real expected semantics should be "flushes out to all replicas and all
> replicas have done posix fsync equivalent - ie the OS has flushed it to the
> disk device (but the disk may have it in its cache)." This jira aims to
> implement the expected behaviour.
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