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https://issues.apache.org/jira/browse/HDFS-5727?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13865046#comment-13865046
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Liang Xie commented on HDFS-5727:
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so far no design doc available, just put the raw thought here as a placeholder,
hopefully start to work on it 3~4 weeks later due to other higher priority
issues need be done these days.
> introduce a self-maintain io queue handling mechanism
> -----------------------------------------------------
>
> Key: HDFS-5727
> URL: https://issues.apache.org/jira/browse/HDFS-5727
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: datanode
> Affects Versions: 3.0.0
> Reporter: Liang Xie
> Assignee: Liang Xie
>
> Currently the datanode read/write SLA is dfficult to be ganranteed for HBase
> online requirement. One of major reasons is we don't support io priority or
> io reqeust reorder inside datanode.
> I proposal introducing a self-maintain io queue mechanism to handle io
> request priority. Image there're lots of concurrent read/write reqeust from
> HBase side, and a background datanode block scanner is running(default is
> every 21 days, IIRC) just in time, then the HBase read/write 99% or 99.9%
> percentile latency would be vulnerable despite we have a bg thread
> throttling...
> the reorder stuf i have not thought clearly enough, but definitely the
> reorder in the queue in the app side would beat the currently relying OS's io
> queue merge.
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