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From "Dave Lerman (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1007) CombinedHiveInputFormat fails with empty input
Date Wed, 16 Jun 2010 00:38:24 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1007?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12879206#action_12879206

Dave Lerman commented on HIVE-1007:

Tried the steps above on Hadoop 0.20.2.  It still logs "number of splits 0", but instead of
hanging at 0%, it completes the map, then fails with a "Shuffle Error: Exceeded MAX_FAILED_UNIQUE_FETCHES;
bailing-out." in the reduce.  This is clearly preferable to hanging and doesn't seem like
a totally unreasonable result when asking for data from an empty file -- should I close the

> CombinedHiveInputFormat fails with empty input
> ----------------------------------------------
>                 Key: HIVE-1007
>                 URL: https://issues.apache.org/jira/browse/HIVE-1007
>             Project: Hadoop Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.4.1
>            Reporter: Dave Lerman
>            Assignee: Dave Lerman
>         Attachments: hive.1007.1.patch
> In a multi-stage query, when one stage returns no data (resulting in a bunch of output
files with size 0), the next stage creates a job with 0 mappers which just sits in the Hadoop
task track forever and hangs the query at 0%.  The issue is that CombineHiveInputFormat looks
for blocks to populate splits, find nones (since input is all 0 bytes), and then returns an
empty array from getSplits.
> There may be good a way to just skip that job altogether, but as a quick hack to get
it working, when there are no splits, I just create a single empty one using the first path
so that the job doesn't hang.

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