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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12412) Change ErasureCodingWorker.stripedReadPool to cached thread pool
Date Wed, 13 Sep 2017 01:30:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16164002#comment-16164002
] 

Hudson commented on HDFS-12412:
-------------------------------

SUCCESS: Integrated in Jenkins build Hadoop-trunk-Commit #12857 (See [https://builds.apache.org/job/Hadoop-trunk-Commit/12857/])
HDFS-12412. Change ErasureCodingWorker.stripedReadPool to cached thread (lei: rev 123342cd0759ff88801d4f5ab10987f6e3f344b0)
* (edit) hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
* (edit) hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSErasureCoding.md
* (edit) hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/erasurecode/ErasureCodingWorker.java
* (edit) hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml


> Change ErasureCodingWorker.stripedReadPool to cached thread pool
> ----------------------------------------------------------------
>
>                 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
>              Labels: hdfs-ec-3.0-nice-to-have
>             Fix For: 3.0.0-beta1
>
>         Attachments: HDFS-12412.00.patch, HDFS-12412.01.patch
>
>
> 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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