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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12136) BlockSender performance regression due to volume scanner edge case
Date Fri, 25 Aug 2017 20:15:01 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16142118#comment-16142118
] 

Kihwal Lee commented on HDFS-12136:
-----------------------------------

I think the performance impact is less severe after HDFS-12157, so we could target 2.8.3 for
the fix. 

> BlockSender performance regression due to volume scanner edge case
> ------------------------------------------------------------------
>
>                 Key: HDFS-12136
>                 URL: https://issues.apache.org/jira/browse/HDFS-12136
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.8.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>         Attachments: HDFS-12136.branch-2.patch, HDFS-12136.trunk.patch
>
>
> HDFS-11160 attempted to fix a volume scan race for a file appended mid-scan by reading
the last checksum of finalized blocks within the {{BlockSender}} ctor.  Unfortunately it's
holding the exclusive dataset lock to open and read the metafile multiple times  Block sender
instantiation becomes serialized.
> Performance completely collapses under heavy disk i/o utilization or high xceiver activity.
 Ex. lost node replication, balancing, or decommissioning.  The xceiver threads congest creating
block senders and impair the heartbeat processing that is contending for the same lock.  Combined
with other lock contention issues, pipelines break and nodes sporadically go dead.



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