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From "Dave Lerman (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1007) CombinedHiveInputFormat fails with empty input
Date Fri, 01 Jan 2010 20:43:54 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1007?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12795792#action_12795792
] 

Dave Lerman commented on HIVE-1007:
-----------------------------------

Here's steps to reproduce:

Using Cloudera's Hadoop 0.20.1+152 (since the CombineFile functionality doesn't work in 0.20.1
without the extra patches), and latest Hive trunk (895060)

SET hive.input.format=org.apache.hadoop.hive.ql.io.CombineHiveInputFormat;
DROP TABLE nullscript;
CREATE TABLE nullscript(KEY STRING, VALUE STRING) STORED AS TEXTFILE;
LOAD DATA LOCAL INPATH 'data/files/nullfile.txt' INTO TABLE nullscript;
select key from nullscript group by key;

>From the log:
2010-01-01 15:36:18,372 INFO  io.CombineHiveInputFormat (CombineHiveInputFormat.java:getSplits(252))
- CombineHiveInputSplit creating pool for /user/hive/warehouse/nullscript
2010-01-01 15:36:18,584 INFO  mapred.FileInputFormat (FileInputFormat.java:listStatus(192))
- Total input paths to process : 1
2010-01-01 15:36:18,781 INFO  io.CombineHiveInputFormat (CombineHiveInputFormat.java:getSplits(262))
- number of splits 0

This yields a MR job with 0 mappers and 1 reducer which hangs in Hadoop at 0%.

> 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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