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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-744) Support hsync in HDFS
Date Fri, 18 May 2012 01:44:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13278488#comment-13278488

Lars Hofhansl commented on HDFS-744:

Thanks Nicholas!

I'll rename the flag and the flush method.

The reason for not calling flush(true) was two-fold:
# Code that currently uses hsync would suddenly get the new behavior. For example HBase which
uses this via a SequenceFile.Writer would have no option to disable this (unless we expose
a new flag to Writer.syncFS).
# Without SYNC_BLOCK it kinda makes no sense (or would at least set the wrong expectation
that everything is sync'ed to disk).

Sorry about the tabs, I had used my default eclipse formatter.
Will look at the Append tests and some new ones for hsync.

> 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.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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