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https://issues.apache.org/jira/browse/HIVE-15178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15655335#comment-15655335
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Sergey Shelukhin commented on HIVE-15178:
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[~prasanth_j] fyi
> ORC stripe merge may produce many MR jobs and no merge if split size is small
> -----------------------------------------------------------------------------
>
> Key: HIVE-15178
> URL: https://issues.apache.org/jira/browse/HIVE-15178
> Project: Hive
> Issue Type: Bug
> Reporter: Sergey Shelukhin
>
> orc_createas1
> logs the following:
> {noformat}
> 2016-11-10T13:38:54,366 INFO [LocalJobRunner Map Task Executor #0]
> mapred.MapTask: Processing split:
> Paths:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/-ext-10004/000001_0:2400+100InputFormatClass:
> org.apache.hadoop.hive.ql.io.orc.OrcFileStripeMergeInputFormat
> 2016-11-10T13:38:54,373 INFO [LocalJobRunner Map Task Executor #0]
> mapred.MapTask: Processing split:
> Paths:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/-ext-10004/000001_0:2500+100InputFormatClass:
> org.apache.hadoop.hive.ql.io.orc.OrcFileStripeMergeInputFormat
> 2016-11-10T13:38:54,380 INFO [LocalJobRunner Map Task Executor #0]
> mapred.MapTask: Processing split:
> Paths:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/-ext-10004/000001_0:2600+100InputFormatClass:
> org.apache.hadoop.hive.ql.io.orc.OrcFileStripeMergeInputFormat
> 2016-11-10T13:38:54,387 INFO [LocalJobRunner Map Task Executor #0]
> mapred.MapTask: Processing split:
> Paths:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/-ext-10004/000001_0:2700+100InputFormatClass:
> org.apache.hadoop.hive.ql.io.orc.OrcFileStripeMergeInputFormat
> ...
> {noformat}
> It tries to merge 2 files, but instead ends up running tons of MR tasks for
> every 100 bytes and produces 2 files again (I assume most tasks don't produce
> the files because the stripes are invalid).
> {noformat}
> 2016-11-10T13:38:53,985 INFO [LocalJobRunner Map Task Executor #0]
> OrcFileMergeOperator: Merged stripe from file
> pfile:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/-ext-10004/000000_0
> [ offset : 3 length: 2770 row: 500 ]
> 2016-11-10T13:38:53,995 INFO [LocalJobRunner Map Task Executor #0]
> exec.AbstractFileMergeOperator: renamed path
> pfile:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/_task_tmp.-ext-10002/_tmp.000002_0
> to
> pfile:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/_tmp.-ext-10002/000002_0
> . File size is 2986
> 2016-11-10T13:38:54,206 INFO [LocalJobRunner Map Task Executor #0]
> OrcFileMergeOperator: Merged stripe from file
> pfile:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/-ext-10004/000001_0
> [ offset : 3 length: 2770 row: 500 ]
> 2016-11-10T13:38:54,215 INFO [LocalJobRunner Map Task Executor #0]
> exec.AbstractFileMergeOperator: renamed path
> pfile:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/_task_tmp.-ext-10002/_tmp.000030_0
> to
> pfile:/Users/sergey/git/hivegit2/itests/qtest/target/warehouse/.hive-staging_hive_2016-11-10_13-38-52_334_1323113125332102866-1/_tmp.-ext-10002/000030_0
> . File size is 2986
> {noformat}
> This is because the test sets the max split size to 100. Merge jobs is
> supposed to override that, but that doesn't happen somehow.
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