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Lefty Leverenz commented on HIVE-3276: -------------------------------------- The configuration parameters are now documented in the wiki: * [hive.optimize.union.remove |https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-hive.optimize.union.remove] * [hive.mapred.supports.subdirectories |https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-hive.mapred.supports.subdirectories] > optimize union sub-queries > -------------------------- > > Key: HIVE-3276 > URL: https://issues.apache.org/jira/browse/HIVE-3276 > Project: Hive > Issue Type: Bug > Affects Versions: 0.10.0 > Reporter: Namit Jain > Assignee: Namit Jain > Fix For: 0.10.0 > > Attachments: HIVE-3276.1.patch, hive.3276.10.patch, > hive.3276.11.patch, hive.3276.12.patch, hive.3276.13.patch, > hive.3276.14.patch, hive.3276.2.patch, hive.3276.3.patch, hive.3276.4.patch, > hive.3276.5.patch, hive.3276.6.patch, hive.3276.7.patch, hive.3276.8.patch, > hive.3276.9.patch > > > It might be a good idea to optimize simple union queries containing > map-reduce jobs in at least one of the sub-qeuries. > For eg: > a query like: > insert overwrite table T1 partition P1 > select * from > ( > subq1 > union all > subq2 > ) u; > today creates 3 map-reduce jobs, one for subq1, another for subq2 and > the final one for the union. > It might be a good idea to optimize this. Instead of creating the union > task, it might be simpler to create a move task (or something like a move > task), where the outputs of the two sub-queries will be moved to the final > directory. This can easily extend to more than 2 sub-queries in the union. > This is very useful if there is a select * followed by filesink after the > union. This can be independently useful, and also be used to optimize the > skewed joins -- > https://cwiki.apache.org/confluence/display/Hive/Skewed+Join+Optimization. > If there is a select, filter between the union and the filesink, the select > and the filter can be moved before the union, and the follow-up job can > still be removed. -- This message was sent by Atlassian JIRA (v6.2#6252)