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https://issues.apache.org/jira/browse/HDFS-4417?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13560185#comment-13560185
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Todd Lipcon commented on HDFS-4417:
-----------------------------------
Can you explain how the new test works? Does it provide an effective regression
test? (ie if you include the new test without this bug fix, does it actually
fail?) I'm not 100% following. Otherwise the change looks good.
> HDFS-347: fix case where local reads get disabled incorrectly
> -------------------------------------------------------------
>
> Key: HDFS-4417
> URL: https://issues.apache.org/jira/browse/HDFS-4417
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, hdfs-client, performance
> Reporter: Todd Lipcon
> Assignee: Colin Patrick McCabe
> Attachments: HDFS-4417.002.patch, HDFS-4417.003.patch,
> HDFS-4417.004.patch, hdfs-4417.txt
>
>
> In testing HDFS-347 against HBase (thanks [~jdcryans]) we ran into the
> following case:
> - a workload is running which puts a bunch of local sockets in the PeerCache
> - the workload abates for a while, causing the sockets to go "stale" (ie the
> DN side disconnects after the keepalive timeout)
> - the workload starts again
> In this case, the local socket retrieved from the cache failed the
> newBlockReader call, and it incorrectly disabled local sockets on that host.
> This is similar to an earlier bug HDFS-3376, but not quite the same.
> The next issue we ran into is that, once this happened, it never tried local
> sockets again, because the cache held lots of TCP sockets. Since we always
> managed to get a cached socket to the local node, it didn't bother trying
> local read again.
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