Oliver Jowett <oliver@opencloud.com> writes:
> This leads to my next problem (which was one of the original reasons I
> went with node replacement): don't we get different performance between
> a parameterized query and an equivalent unparameterized query in cases
> such as this? :
> SELECT * FROM sometable WHERE field = $1 * 10
I don't think the run-time performance would be materially different in
most cases. What might happen is that if the selectivity functions are
stupid, they would fail to reduce the comparison value to a constant and
thus not be able to arrive at a good selectivity estimate, thus leading
to a bad plan choice. However we need not put up with the selectivity
functions being that stupid. I think it would be reasonable to
constant-fold expressions involving known parameter values *within the
context of selfuncs.c only*. This would let us get good estimates
without giving up the usability of the plan for fresh parameter values.
regards, tom lane
