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https://issues.apache.org/jira/browse/HDFS-9107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14900352#comment-14900352
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Yi Liu commented on HDFS-9107:
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Sorry I just see Steve's comments.
{quote}
cores on different sockets may give different answers
{quote}
About the {{nanoTime}}, yes, I also ever saw similar points and discussion like
this, but seems it's not correct and {{nanoTime}} is safe, see more discussion
in
http://stackoverflow.com/questions/510462/is-system-nanotime-completely-useless.
(There are some links to oracle article.)
> 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
>
>
> 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 cycle.
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