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https://issues.apache.org/jira/browse/HDFS-12412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16159682#comment-16159682
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Kai Zheng commented on HDFS-12412:
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Thanks Eddy for the ping.
The idea to remove the striped read pool and reuse the same reconstruction pool
sounds good to me, since given the later and the most often used erasure codec,
we can roughly estimate the striped read threads need. We can also simplify the
configuration and codes.
So as you said, you probably have the idea how to reduce the recommended value
or default value and validate the configuration value for the reconstruction
pool size, assuming you know how many concurrent reconstruction tasks to be
performed and so on.
Less configuration with reasonable defaults would make the brand feature more
easier to use. When needed, we can fine-tune and add more later.
> Remove ErasureCodingWorker.stripedReadPool
> ------------------------------------------
>
> Key: HDFS-12412
> URL: https://issues.apache.org/jira/browse/HDFS-12412
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: erasure-coding
> Affects Versions: 3.0.0-alpha3
> Reporter: Lei (Eddy) Xu
> Assignee: Lei (Eddy) Xu
>
> In {{ErasureCodingWorker}}, it uses {{stripedReconstructionPool}} to schedule
> the EC recovery tasks, while uses {{stripedReadPool}} for the reader threads
> in each recovery task. We only need one of them to throttle the speed of
> recovery process, because each EC recovery task has a fix number of source
> readers (i.e., 3 for RS(3,2)). And because of the findings in HDFS-12044, the
> speed of EC recovery can be throttled by {{strippedReconstructionPool}} with
> {{xmitsInProgress}}.
> Moreover, keeping {{stripedReadPool}} makes customer difficult to understand
> and calculate the right balance between
> {{dfs.datanode.ec.reconstruction.stripedread.threads}},
> {{dfs.datanode.ec.reconstruction.stripedblock.threads.size}} and
> {{maxReplicationStreams}}. For example, a small {{stripread.threads}}
> (comparing to which {{reconstruction.threads.size}} implies), will
> unnecessarily limit the speed of recovery, which leads to larger MTTR.
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