Greg Stark <gsstark@mit.edu> writes:
> Tom Lane <tgl@sss.pgh.pa.us> writes:
>> I think the one effect that's not being modeled is amortization of index
>> fetches across successive queries.

> And across multiple fetches in a single query, such as with a nested loop.

Right, that's effectively the same problem. You could imagine making a
special-purpose solution for nestloop queries but I think the issue is
more general than that.

> It seems like the effective_cache_size parameter should be having some
> influence here.

But it doesn't :-(. e_c_s is currently only used to estimate
amortization of repeated heap-page fetches within a single indexscan.

regards, tom lane

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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match