Re: minimal update

Andrew Dunstan wrote:
>
>
> Tom Lane wrote:
>> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>>
>>> How does this look?
>>>
>>
>>
>>> if (newtuple->t_len == oldtuple->t_len &&
>>> newtuple->t_data->t_hoff == oldtuple->t_data->t_hoff &&
>>> HeapTupleHeaderGetNatts(newtuple) ==
>>> HeapTupleHeaderGetNatts(oldtuple) &&
>>> (newtuple->t_data->t_infomask & (HEAP_HASOID|HEAP_HASNULL))
>>> == (oldtuple->t_data->t_infomask & (HEAP_HASOID|HEAP_HASNULL)) &&
>>> memcmp(newtuple->t_data + offsetof(HeapTupleHeaderData,
>>> t_bits),
>>> oldtuple->t_data + offsetof(HeapTupleHeaderData, t_bits)
>>> newtuple->t_len - offsetof(HeapTupleHeaderData,
>>> t_bits)) == 0)
>>>
>>
>>
>>> rettuple = NULL;
>>>
>>
>> Looks sane. It might be even saner if you compare all of the
>> non-visibility-related infomask bits, viz
>>
>> (newtuple->t_data->t_infomask & ~HEAP_XACT_MASK) ==
>> (oldtuple->t_data->t_infomask & ~HEAP_XACT_MASK)
>>
>> rather than just HASOID and HASNULL.
>>
>>
>>
>
> Sadly, the memcmp is failing on my test ("update foo set bar = bar")
> on 8.2. Looks like I'm in for weekend with my fave debugger :-(
>
>

Turns out we needed those pointers used in the arguments to memcmp cast
to char * so the pointer arithmetic would work right.

I'll be suggesting we add a utility function like this for 8.4.

cheers

andrew