Recently I came across a case where the planner choose larger table on hash side. I am not sure whether it is an intended behavior or we are missing something.
I have two tables (a and b) each with single column in it. One table 'a' is large with around 30 million distinct rows and other table 'b' has merely 70,000 rows with one-seventh (10,000) distinct rows. I have analyzed both the table. But while joining both the table I get the larger table on hash side.
tpch=# explain select b from b left join a on a = b;
I would like to know the reason for choosing this plan and Is there a easy fix to prevent such plans (especially like this one where it choose a larger hash table) ?