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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-744) Support hsync in HDFS
Date Wed, 26 Sep 2012 04:40:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13463512#comment-13463512
] 

Lars Hofhansl commented on HDFS-744:
------------------------------------

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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