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https://issues.apache.org/jira/browse/HDFS-12778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16251896#comment-16251896
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Íñigo Goiri commented on HDFS-12778:
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Can we add explicit unit tests for corner cases like:
# Only one DN with PROVIDED
# Less DNs with PROVIDED than default replication
# More blocks than DNs (trying to fill the excluded nodes)
Should we make the block locations deterministic to some degree?
I can see two mappers trying to accessing the same block and in that way some
caching could be done.
> [READ] Report multiple locations for PROVIDED blocks
> ----------------------------------------------------
>
> Key: HDFS-12778
> URL: https://issues.apache.org/jira/browse/HDFS-12778
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Virajith Jalaparti
> Assignee: Virajith Jalaparti
> Attachments: HDFS-12778-HDFS-9806.001.patch
>
>
> On {{getBlockLocations}}, only one Datanode is returned as the location for
> all PROVIDED blocks. This can hurt the performance of applications which
> typically 3 locations per block. We need to return multiple Datanodes for
> each PROVIDED block for better application performance/resilience.
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