Re: Using HeapTuple.t_len to verify size of tuple

Vignesh Raghunathan <vignesh(dot)pgsql(at)gmail(dot)com> writes:
> On Tue, Aug 25, 2015 at 2:56 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> If t_len were *less* than that, it would be a bug. But I think it's
>> fairly common for t_len to be rounded up to the next maxalign boundary.

> I have modified heap_deform_tuple code to check whether the 'off' variable
> matches the tuple's t_len field for a project. In the code, off is not
> updated in case of null fields. However, when I run it for pg_class table,
> the code throws an error saying that the value of off does not match t_len.
> It turns out that for all tuples even if the attribute attacl is null,
> t_len field is set to be the sizeof(FormData_pg_class).

You mean "even if relacl is not null"? Sounds improbable: AFAIR, pg_class
tuples are built with heap_form_tuple, same as anything else.

regards, tom lane