The next query has three small tables and expected broadcast join, but not.
select count(*) from large1
left outer join large2 on large1_id = large2_id
left outer join small1 on large1_id = small1_id
left outer join small2 on large1_id = small2_id
left outer join small3 on large1_id = small3_id
The next is the upper query's plan.
Optimized plan should be the next.
|-eb_1404411906426_0000_000003 (broadcast small1, small2, small3)