Re: HashJoin order, hash the large or small table? Postgres likes to hash the big one, why?

Scott Carey wrote:
>
> If the cost to hash is 1200493, and it needs to probe the hash 20241 times, why would the total cost be 631471410?
Thecost to probe can't be that big! A cost of 500 to probe and join?   
> Why favor hashing the large table and probing with the small values rather than the other way around?
>
>

May I ask a stupid question: how is the query cost calculated? What are
the units? I/O requests? CPU cycles? Monopoly money?


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