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https://issues.apache.org/jira/browse/HDFS-6450?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14061760#comment-14061760
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Liang Xie commented on HDFS-6450:
---------------------------------
After a deep looking, it's kind of hard to reuse/maintain block reader as
before.
In pread(), we don't have this trouble, because we always create new block
reader.
In read(), if we want to support hedged read ability, in general:
1) first read(r1) using the old block reader if possible, then wait hedged read
timeout setting
2) second read(r2) must create a new block reader, and submit into thread pool
3) wait the first completed task, and return final read result to client side.
Here we need to set(remember) this task's block reader to DFIS's block reader
variable, and should keep it open, but we also need to close the other block
reader to avoid leak.
Another thing need to know is that if we remember the faster block reader, if
it's a remote block reader, then the following read() will bypass local read in
the following r1 operations...
Any thought ? [~cmccabe], [[email protected]] ...
> Support non-positional hedged reads in HDFS
> -------------------------------------------
>
> Key: HDFS-6450
> URL: https://issues.apache.org/jira/browse/HDFS-6450
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.4.0
> Reporter: Colin Patrick McCabe
> Assignee: Liang Xie
> Attachments: HDFS-6450-like-pread.txt
>
>
> HDFS-5776 added support for hedged positional reads. We should also support
> hedged non-position reads (aka regular reads).
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