Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Dec 5, 2011 at 2:47 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
>>> To clarify, I believe the rule is that the first variable-length field
>>> can be accessed as a struct field. Are there any exceptions to this?
>> If it is known not null, yes, but I wonder just how many places actually
>> depend on that.
> My impression is that all the varlena fields also allow nulls.
See MARKNOTNULL in bootstrap.c. I think the exceptions were designed to
protect direct accesses to pg_index.
regards, tom lane