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https://issues.apache.org/jira/browse/HIVE-6134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13863525#comment-13863525
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Ashutosh Chauhan commented on HIVE-6134:
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I don't think because an external tool (Hue) is failing to read data because of
too many files, its Hive's responsibility to compact files. Hue should be fixed
not to time out while reading too many files.
> Merging small files based on file size only works for CTAS queries
> ------------------------------------------------------------------
>
> Key: HIVE-6134
> URL: https://issues.apache.org/jira/browse/HIVE-6134
> Project: Hive
> Issue Type: Bug
> Affects Versions: 0.8.0, 0.10.0, 0.11.0, 0.12.0
> Reporter: Eric Chu
>
> According to the documentation, if we set hive.merge.mapfiles to true, Hive
> will launch an additional MR job to merge the small output files at the end
> of a map-only job when the average output file size is smaller than
> hive.merge.smallfiles.avgsize. Similarly, by setting hive.merge.mapredfiles
> to true, Hive will merge the output files of a map-reduce job.
> My expectation is that this is true for all MR queries. However, my
> observation is that this is only true for CTAS queries. In
> GenMRFileSink1.java, HIVEMERGEMAPFILES and HIVEMERGEMAPREDFILES are only used
> if ((ctx.getMvTask() != null) && (!ctx.getMvTask().isEmpty())). So, for a
> regular SELECT query that doesn't have move tasks, these properties are not
> used.
> Is my understanding correct and if so, what's the reasoning behind the logic
> of not supporting this for regular SELECT queries? It seems to me that this
> should be supported for regular SELECT queries as well. One scenario where
> this hits us hard is when users try to download the result in HUE, and HUE
> times out b/c there are thousands of output files. The workaround is to
> re-run the query as CTAS, but it's a significant time sink.
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