On Tue, Aug 25, 2015 at 2:56 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Vignesh Raghunathan <vignesh.pgsql@gmail.com> writes: > Can the t_len field in HeapTuple structure be used to verify the length of > the tuple?
> That is, if I calculate the length from the contents of the tuple using > data from pg_attribute for fixed length fields and the data from the header > for varlena fields, should it always match the value stored in t_len?
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.
regards, tom lane
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). Is this normal behavior?
