Re: 9.1 plperlu bug with null rows in trigger hash

On Mon, May 23, 2011 at 14:59, Greg Sabino Mullane <greg@endpoint.com> wrote:
> I've not been able to duplicate this in a standalone script yet,
> but in the guts of Bucardo is a trigger function called validate_goat()
> that is giving this error on 9.1 HEAD, but not on previous versions:
>
> "Failed to add table "public.pgbench_tellers": DBD::Pg::st execute
> failed: ERROR:  Modification of non-creatable hash value attempted,
> subscript "pkey" at line 4."

> ...
> Some Googling suggests it might
> be because we are using &PL_sv_undef instead of a proper
> newSV(0).

Yep. Per http://search.cpan.org/~jesse/perl-5.14.0/pod/perlguts.pod#AVs,_HVs_and_undefined_values

|...For example, intuition tells you that this XS code:
|
|    AV *av = newAV();
|    av_store( av, 0, &PL_sv_undef );
|
| is equivalent to this Perl code:
|
|    my @av;
|    $av[0] = undef;
| Unfortunately, this isn't true. AVs use &PL_sv_undef as a marker for
indicating that an array element has not yet been initialized.

We have a few places that have that pattern :-(.

I was able to reproduce it fairly easily(1) by passing in NULL values
explicitly. Fixed in the attached.

I looked at 9.0 and below and they did this correctly. This code path
was heavily re-factored in 9.1 for better array and composite type
support . As noted in perlguts using &PL_sv_undef follows your
intuition, but its wrong :-(. Classic perl xs I suppose.

Greg, can you confirm the attached fixes it for you?

--
[1]
=> create or replace function td() returns trigger language plperlu as
$bc$
$_TD->{new}{a} = 1;
return 'MODIFY';
$bc$;
CREATE FUNCTION

=>  create table trig_test(a int);
CREATE TABLE

=> create trigger test_trig before insert on trig_test for each row
execute procedure td();
CREATE TRIGGER

=> insert into trig_test values (NULL);
CONTEXT:  PL/Perl function "td"
ERROR:  Modification of non-creatable hash value attempted, subscript
"a" at line 2.