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https://issues.apache.org/jira/browse/HDFS-13640?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Duo Zhang reopened HDFS-13640:
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> enable ShortCircuit Read on UC block
> ------------------------------------
>
> Key: HDFS-13640
> URL: https://issues.apache.org/jira/browse/HDFS-13640
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 3.0.2
> Reporter: Gang Xie
> Priority: Major
>
> The ShortCircuit read is disabled by HDFS-2757 due to the inconsistency of
> the block states. With this limitation, some streaming/messaging application
> could not benefit the performance improvement from SCR. In our streaming
> system whose storage is HDFS, has around 90% read on the last blocks. So,
> it's necessary to enable SCR on the last block, especially the app could
> ensure the read after the flush.
> After look into the original issue in HDFS-2757, it could only happen when
> the read beyond the flush or the local datanode is kicked out from the
> pipeline. But if there is the data and the visible length of the block covers
> the read length, we could still read the data from the block, right?
>
> I didn't get a completed solution here. Any suggestion could be helpful.
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