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https://issues.apache.org/jira/browse/HDFS-744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13463373#comment-13463373
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Kan Zhang commented on HDFS-744:
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bq. As long as the syncs (or flushes) are not serialized it's fine (otherwise
nobody is going to switch this on).
I must be missing something here, but why can't we move the enqueuing of seqno
in receivePacket() back to after flushOrSync() is done, essentially reverting
the change made by HDFS-265? In doing so, hflush will be implementing API4
instead of API3.
> 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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