Re: BUG #18676: Execute function while selecting from table with partial index using this function.

PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> Please run the script below. It creates sample table with partial index
> using IMMUTABLE function.
> I think when table is changing - index in changing and thus function used in
> WHERE cluse can be run.
> But it is not supposed to be run on just simple SELECT from table without
> even condition to use this index.

[ shrug... ] There is no bug here. The planner is entitled to
investigate the properties of indexes attached to a table it's
trying to plan for. Sure, this index is not relevant to this
query --- but how's the planner going to know that without
examining the index? And part of that examination involves
reducing any partial-index predicate to standard form, which
includes constant-folding. Since your function is marked
IMMUTABLE, that means it should be evaluated and reduced to
a constant.

Part of the contract for marking a function IMMUTABLE is that
it has no interesting side-effects. This example breaks that
in two ways: the RAISE NOTICE is a side-effect, and the
possibility of a permissions failure is another one.

regards, tom lane