Re: merge>hash>loop

Mark Kirkwood <markir@paradise.net.nz> writes:
> Jim C. Nasby wrote:
>> Good point. :/ I'm guessing there's no easy way to see how many blocks
>> for a given relation are in shared memory, either...

> contrib/pg_buffercache will tell you this -

I think the key word in Jim's comment was "easy", ie, cheap.  Grovelling
through many thousands of buffers to count the matches to a given
relation doesn't sound appetizing, especially not if it gets done over
again several times during each query-planning cycle.  Trying to keep
centralized counts somewhere would be even worse (because of locking/
contention issues).

            regards, tom lane