Re: minimal update

Tom Lane wrote:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>
>> Tom Lane wrote:
>>
>>> A BEFORE UPDATE trigger would be better, and probably hardly more
>>> expensive than a wired-in facility (especially if you were willing to
>>> write it in C).
>>>
>
>
>> Yes. I also prefer the trigger idea to a rule because triggers are easy
>> to enable and disable. It's still a lot of work for what must be a
>> common want, though. Could it be done generically?
>>
>
> Well, you could write the trigger in C and it'd work for any table.
> I think it could be as simple as a memcmp of the tuples' data areas,
> since we now require padding bytes to be 0 ...
>
>
>

Something like this fragment?

newtuple = trigdata->tg_newtuple;
oldtuple = trigdata->tg_trigtuple;
rettuple = newtuple;

if (newtuple->t_len == oldtuple->t_len &&
newtuple->t_data->t_hoff == oldtuple->t_data->t_hoff &&
memcmp(GETSTRUCT(newtuple),GETSTRUCT(oldtuple),
newtuple->t_len - newtuple->t_data->t_hoff) == 0)
rettuple = NULL;

return PointerGetDatum(rettuple);

Also, when did we first require padding bytes to be 0?

cheers

andrew