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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-744) Support hsync in HDFS
Date Wed, 23 May 2012 21:43:40 GMT

    [ https://issues.apache.org/jira/browse/HDFS-744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13281942#comment-13281942
] 

Todd Lipcon commented on HDFS-744:
----------------------------------

Looks pretty good! Just a few small things:

- looks like hard tabs still snuck in one spot
- I don't think hsync() needs to be synchronized: ie further writes could proceed to the stream
while an earlier writer is waiting on a sync response

----
{code}
    // repeated hsyncs, not avoiding unnecessary sync here
    out.hsync();
    checkSyncMetric(cluster, 2);
{code}

maybe add a note that says more explicitly something like: this is a potential future optimization
that is not yet implemented, or something?
                
> 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
>         Attachments: 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.patch,
hdfs-744-v2.txt, hdfs-744-v3.txt, hdfs-744.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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