A bucket map join is a special type of map join applied on the bucket tables. To enable a bucket map join, we need to enable the following settings:

> SET hive.auto.convert.join=true; 
> SET hive.optimize.bucketmapjoin=true; -- default false

In a bucket map join, all the join tables must be bucket tables and join on bucket columns. In addition, the bucket number in the bigger tables must be a multiple of the bucket number in the smaller tables.