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https://issues.apache.org/jira/browse/HDFS-744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13463505#comment-13463505
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Lars Hofhansl commented on HDFS-744:
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I think the problem is that we have to enqueue the seqno before the packet is
sent downstream right? (Otherwise we could potentially miss the ack, right?)
So in order to enqueue the seqno after we syncOrFlush, we'd also have to send
the packet downstream after we syncOrFlush, which essentially means that we are
serializing the sync times across all replicas.
> 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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