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  • Consider the possibility of multiple map-joins on different keys:
    Code Block
    select /*+MAPJOIN(smallTableTwo)*/ idOne, idTwo, value FROM
  ( select /*+MAPJOIN(smallTableOne)*/ idOne, idTwo, value FROM
    bigTable JOIN smallTableOne on (bigTable.idOne = smallTableOne.idOne)                                                   
  ) firstjoin                                                             
  JOIN                                                                  
  smallTableTwo on (firstjoin.idTwo = smallTableTwo.idTwo)

The above query is not supported. Without the mapjoin hint, the above query would be executed as 2 map-only jobs. If the user knows in advance that the inputs are small enough to fit in memory, the following configurable parameters can be used to make sure that the query executes in a single map-reduce job.

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