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https://issues.apache.org/jira/browse/HDFS-895?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12931180#action_12931180
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Nicolas Spiegelberg commented on HDFS-895:
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+1 peer reviewed this. looks pretty solid.
> Allow hflush/sync to occur in parallel with new writes to the file
> ------------------------------------------------------------------
>
> Key: HDFS-895
> URL: https://issues.apache.org/jira/browse/HDFS-895
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs client
> Affects Versions: 0.22.0
> Reporter: dhruba borthakur
> Assignee: Todd Lipcon
> Fix For: 0.22.0
>
> Attachments: 895-delta-for-review.txt, hdfs-895-0.20-append.txt,
> hdfs-895-20.txt, hdfs-895-review.txt, hdfs-895-trunk.txt, hdfs-895.txt,
> hdfs-895.txt, hdfs-895.txt
>
>
> In the current trunk, the HDFS client methods writeChunk() and hflush./sync
> are syncronized. This means that if a hflush/sync is in progress, an
> applicationn cannot write data to the HDFS client buffer. This reduces the
> write throughput of the transaction log in HBase.
> The hflush/sync should allow new writes to happen to the HDFS client even
> when a hflush/sync is in progress. It can record the seqno of the message for
> which it should receice the ack, indicate to the DataStream thread to star
> flushing those messages, exit the synchronized section and just wai for that
> ack to arrive.
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