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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-9107) Prevent NN's unrecoverable death spiral after full GC
Date Mon, 21 Sep 2015 20:17:06 GMT

     [ https://issues.apache.org/jira/browse/HDFS-9107?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Daryn Sharp updated HDFS-9107:
    Attachment: HDFS-9107.patch

Use a stopwatch to abort processing in the inner heartbeat checking loop, and then check at
end of the entire scan for whether to skip next scan.  Even added a meager test.

> Prevent NN's unrecoverable death spiral after full GC
> -----------------------------------------------------
>                 Key: HDFS-9107
>                 URL: https://issues.apache.org/jira/browse/HDFS-9107
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.0.0-alpha
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>         Attachments: HDFS-9107.patch, HDFS-9107.patch
> A full GC pause in the NN that exceeds the dead node interval can lead to an infinite
cycle of full GCs.  The most common situation that precipitates an unrecoverable state is
a network issue that temporarily cuts off multiple racks.
> The NN wakes up and falsely starts marking nodes dead. This bloats the replication queues
which increases memory pressure. The replications create a flurry of incremental block reports
and a glut of over-replicated blocks.
> The "dead" nodes heartbeat within seconds. The NN forces a re-registration which requires
a full block report - more memory pressure. The NN now has to invalidate all the over-replicated
blocks. The extra blocks are added to invalidation queues, tracked in an excess blocks map,
etc - much more memory pressure.
> All the memory pressure can push the NN into another full GC which repeats the entire

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