Re: minimal update

Bruce Momjian wrote:
> Andrew Dunstan wrote:
>
>> Right. In fact, I already had that part in fact - see
>> http://people.planetpostgresql.org/andrew/index.php?/archives/22-Minimal-Update-Trigger.html
>>
>> What I was waiting for was the part where it gets put in the catalog,
>> documented, etc.
>>
>
> I can probably do that part. Send over what you have and I will work on
> it. Thanks.
>
>

It's very similar to what Gurjeet posted (but designed to work with
earlier postgres versions)

cheers

andrew

---

|#include "postgres.h"
#include "commands/trigger.h"
#include "access/htup.h"

#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif

/* for pre 8.3 */
#ifndef HeapTupleHeaderGetNatts
#define HeapTupleHeaderGetNatts(th) ( (th)->t_natts )
#endif

extern Datum min_update_trigger(PG_FUNCTION_ARGS);

PG_FUNCTION_INFO_V1(min_update_trigger);

Datum
min_update_trigger(PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *) fcinfo->context;
HeapTuple newtuple, oldtuple, rettuple;

/* make sure it's called as a trigger at all */
if (!CALLED_AS_TRIGGER(fcinfo))
elog(ERROR, "min_update_trigger: not called by trigger manager");

/* and that it's called on update */
if (! TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
elog(ERROR, "min_update_trigger: not called on update");

/* and that it's called before update */
if (! TRIGGER_FIRED_BEFORE(trigdata->tg_event))
elog(ERROR, "min_update_trigger: not called before update");

/* and that it's called for each row */
if (! TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
elog(ERROR, "min_update_trigger: not called for each row");

/* get tuple dat, set default return */
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 PointerGetDatum(rettuple);
}|