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https://issues.apache.org/jira/browse/HDFS-5366?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13817613#comment-13817613
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Colin Patrick McCabe commented on HDFS-5366:
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here's a new patch incorporating Chris' fix.
The overall idea here is to keep lists of replicas to cache/uncache around
until the DN replies and says that they've been acted on. This is different
than the current scheme, where they are "fire and forget."
To prevent re-sending these commands too often, this introduces a per-DN timer
which sets the maximum rate at which commands can be re-sent. (This timer can
be overridden by the cache rescanner thread changing what should be cached,
though.)
> recaching improvements
> ----------------------
>
> Key: HDFS-5366
> URL: https://issues.apache.org/jira/browse/HDFS-5366
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Affects Versions: 3.0.0
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Attachments: HDFS-5366-caching.001.patch, HDFS-5366.002.patch
>
>
> There are a few things about our HDFS-4949 recaching strategy that could be
> improved.
> * We should monitor the DN's maximum and current mlock'ed memory consumption
> levels, so that we don't ask the DN to do stuff it can't.
> * We should not try to initiate caching on stale or decomissioning DataNodes
> (although we should not recache things stored on such nodes until they're
> declared dead).
> * We might want to resend the {{DNA_CACHE}} or {{DNA_UNCACHE}} command a few
> times before giving up. Currently, we only send it once.
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