Tom Lane wrote:
Andrew Dunstan <[EMAIL PROTECTED]> writes:
Tom Lane wrote:
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);
Close, but I think you also need to take care to compare natts and
the null bitmaps (if any). Might be worth comparing OIDs too, though
AFAIR there is no mechanism for substituting a different OID during
UPDATE. Probably the easiest coding is to memcmp all the way from
offsetof(t_bits) to t_len, after comparing natts and the HASNULL and
HASOID flags.
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;
return PointerGetDatum(rettuple);
cheers
andrew
Also, when did we first require padding bytes to be 0?
The 8.3 varvarlena patch is what requires it, but in practice
heap_formtuple has always started with a palloc0, so I think it would
work a long ways back.
regards, tom lane
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