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No Format |
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set hive.auto.convert.join=true; select count(*) from store_sales join time_dim on (ss_sold_time_sk = t_time_sk) |
The default value for hive.auto.convert.join was false in Hive 0.10.0. Hive 0.11.0 changed the default to true (HIVE-3297). Note that hive-default.xml.template incorrectly gives the default as false in Hive 0.11.0 through 0.13.1.
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- Merge M*-MR patterns into a single MR.
- Merge MJ->MJ into a single MJ when possible.
- Merge MJ* patterns into a single Map stage as a chain of MJ operators. (Not yet implemented.)
If hive.auto.convert.join
is set to true the optimizer not only converts joins to mapjoins but also merges MJ* patterns as much as possible.
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