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https://issues.apache.org/jira/browse/HIVE-900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12769602#action_12769602
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Ning Zhang commented on HIVE-900:
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distributed cache is definitely one option. It seems it also works on copying
file from hdfs: uri in addition to local directory. However based on the
documentation of distributed cache, the cached file should be copied at the
beginning of the mapper task. This may also have the same network inbound
congestion issue if 3000 mappers are trying to copy the same file at the same
time. Or is the distributed cache uses a smarter copying mechanism (like
hierarchical rather than 1:ALL)? Otherwise distributing the jar file will face
the same issue.
> Map-side join failed if there are large number of mappers
> ---------------------------------------------------------
>
> Key: HIVE-900
> URL: https://issues.apache.org/jira/browse/HIVE-900
> Project: Hadoop Hive
> Issue Type: Improvement
> Reporter: Ning Zhang
> Assignee: Ning Zhang
>
> Map-side join is efficient when joining a huge table with a small table so
> that the mapper can read the small table into main memory and do join on each
> mapper. However, if there are too many mappers generated for the map join, a
> large number of mappers will simultaneously send request to read the same
> block of the small table. Currently Hadoop has a upper limit of the # of
> request of a the same block (250?). If that is reached a
> BlockMissingException will be thrown. That cause a lot of mappers been
> killed. Retry won't solve but worsen the problem.
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