Re: [HACKERS] [PATCH] Generic type subscripting

So ... one of the things that's been worrying me about this patch
from day one is whether it would create a noticeable performance
penalty for existing use-cases. I did a small amount of experimentation
about that with the v35 patchset, and it didn't take long at all to
find that this:

--- cut ---
create or replace function arraytest(n int) returns void as
$$
declare
a int[];
begin
a := array[1, 1];
for i in 3..n loop
a[i] := a[i-1] - a[i-2];
end loop;
end;
$$
language plpgsql stable;

\timing on

select arraytest(10000000);
--- cut ---

is about 15% slower with the patch than with HEAD. I'm not sure
what an acceptable penalty might be, but 15% is certainly not it.

I'm also not quite sure where the cost is going. It looks like
0001+0002 aren't doing much to the executor except introducing
one level of subroutine call, which doesn't seem like it'd account
for that.

I don't think this can be considered RFC until the performance
issue is addressed.

regards, tom lane