minimal update trigger

As discussed a little while back, I would like to add a generic trigger 
function which will force an update to skip if the new and old tuples 
are identical.

The guts of this is the following snippet of code:

|        rettuple  = newtuple = trigdata->tg_newtuple;       oldtuple = trigdata->tg_trigtuple;
       if (newtuple->t_len == oldtuple->t_len &&           newtuple->t_data->t_hoff == oldtuple->t_data->t_hoff &&
    HeapTupleHeaderGetNatts(newtuple->t_data) == HeapTupleHeaderGetNatts(oldtuple->t_data) &&
(newtuple->t_data->t_infomask& ~HEAP_XACT_MASK) ==            (oldtuple->t_data->t_infomask & ~HEAP_XACT_MASK) &&
   memcmp(((char *)newtuple->t_data) + offsetof(HeapTupleHeaderData, t_bits),                  ((char
*)oldtuple->t_data)+ offsetof(HeapTupleHeaderData, t_bits),                    newtuple->t_len -
offsetof(HeapTupleHeaderData,t_bits)) == 0)       {           rettuple = NULL;       }
 
       return rettuple;


I propose to call the function pg_minimal_update.

Unless there is an objection I will put together a patch + docs for this shortly. Not quite sure what section of the
docsto put it in - maybe a new subsection of the Functions chapter?
 


cheers

andrew
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