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Namit Jain commented on HIVE-3784: ---------------------------------- bq. Reading from code it feels like that its not possible to have a) union before mapjoin b) union after mapjoin c) common join after mapjoin. Union before/after mapjoin hint will not be supported -- That is not true completely. Without a map-join hint, joins before/after union will automatically get converted to a map-join. There is nothing which was supported before and will not be in future - it will work without the hint. bq. common join after mapjoin Same thing. The only small case if for sort-merge joins, which I added recently in HIVE-3633. This will also be made automatic soon. I will address your other comments. > de-emphasize mapjoin hint > ------------------------- > > Key: HIVE-3784 > URL: https://issues.apache.org/jira/browse/HIVE-3784 > Project: Hive > Issue Type: Improvement > Components: Query Processor > Reporter: Namit Jain > Assignee: Namit Jain > Attachments: hive.3784.10.patch, hive.3784.11.patch, > hive.3784.12.patch, hive.3784.13.patch, hive.3784.14.patch, > hive.3784.15.patch, hive.3784.16.patch, hive.3784.1.patch, hive.3784.2.patch, > hive.3784.3.patch, hive.3784.4.patch, hive.3784.5.patch, hive.3784.6.patch, > hive.3784.7.patch, hive.3784.8.patch, hive.3784.9.patch > > > hive.auto.convert.join has been around for a long time, and is pretty stable. > When mapjoin hint was created, the above parameter did not exist. > The only reason for the user to specify a mapjoin currently is if they want > it to be converted to a bucketed-mapjoin or a sort-merge bucketed mapjoin. > Eventually, that should also go away, but that may take some time to > stabilize. > There are many rules in SemanticAnalyzer to handle the following trees: > ReduceSink -> MapJoin > Union -> MapJoin > MapJoin -> MapJoin > This should not be supported anymore. In any of the above scenarios, the > user can get the mapjoin behavior by setting hive.auto.convert.join to true > and not specifying the hint. This will simplify the code a lot. > What does everyone think ? -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira