An SMBM join is a special bucket join but triggers a map-side join only. It can avoid caching all rows in the memory like a map join does. To perform SMBM joins, the join tables must have the same bucket, sort, and join condition columns. To enable such joins, we need to enable the following settings:
> SET hive.auto.convert.join=true; > SET hive.auto.convert.sortmerge.join=true > SET hive.optimize.bucketmapjoin=true; > SET hive.optimize.bucketmapjoin.sortedmerge=true; > SET hive.auto.convert.sortmerge.join.noconditionaltask=true; > SET hive.auto.convert.sortmerge.join.bigtable.selection.policy=org.apache.hadoop.hive.ql.optimizer.TableSizeBasedBigTableSelectorForAutoSMJ;
