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https://issues.apache.org/jira/browse/HDFS-744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13463512#comment-13463512
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Lars Hofhansl commented on HDFS-744:
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Another approach would be to wait in the responder until both the downstream
datanode responded *and* the sync has finished. That way we get correctness and
we can still interleave sync'ing/RTT in the pipeline.
> Support hsync in HDFS
> ---------------------
>
> Key: HDFS-744
> URL: https://issues.apache.org/jira/browse/HDFS-744
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: data-node, hdfs client
> Reporter: Hairong Kuang
> Assignee: Lars Hofhansl
> Fix For: 2.0.2-alpha
>
> Attachments: HDFS-744-2.0-v1.patch, HDFS-744-2.0-v2.patch,
> HDFS-744-trunk.patch, HDFS-744-trunk-v2.patch, HDFS-744-trunk-v3.patch,
> HDFS-744-trunk-v4.patch, HDFS-744-trunk-v5.patch, HDFS-744-trunk-v6.patch,
> HDFS-744-trunk-v7.patch, HDFS-744-trunk-v8.patch, hdfs-744.txt,
> hdfs-744-v2.txt, hdfs-744-v3.txt
>
>
> 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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