Jeff Janes <jeff.janes@gmail.com> writes:
> count(*) and sum(1) do different things internally, and in my hands
> sum(1) is ~10% slower.
> I don't know how to dump the output of ExecBuildProjectionInfo into a
> human readable form, so I don't know the basis of the difference. But
> I wonder if using count(*) would lower the weight of the ExecProject
> function.
Probably. count() doesn't actually have any arguments, so there's
nothing for ExecProject to do. sum(1) invokes the generic case there
(ExecTargetList). I suppose we could add another special-case path for
constant tlist elements, but I suspect that would mostly be optimizing
for benchmarks rather than helping real-world cases.
regards, tom lane