From the directory listing, your table must have "transactional=true" property, i.e. it's an ACID table. That means that Insert Overwrite will create a base_x directory where it will put the result of the insert (new data) there. Any data that existed before, will remain in the table but will not be visible to readers that start after Insert Overwrite finished. Old data will be physically removed once Compaction runs over this table/partition.