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The "Hive/LanguageManual/Joins" page has been changed by NamitJain. http://wiki.apache.org/hadoop/Hive/LanguageManual/Joins?action=diff&rev1=12&rev2=13 -------------------------------------------------- SELECT a.key, a.val FROM a LEFT SEMI JOIN b on (a.key = b.key) }}} + * If the tables being joined are bucketized, and the buckets are a multiple of each other, the buckets can be joined with each other. If table A has 8 buckets are table B has 4 buckets, the following join + {{{ + SELECT /*+ MAPJOIN(b) */ a.key, a.value + FROM a join b on a.key = b.key + }}} + will be done on the mapper only. Instead of fetching B completely for each mapper of A, only the required buckets are fetched. For the query above, the mapper processing bucket 1 for A will only fetch bucket 1 of B
