Re: minimal update - Mailing list pgsql-hackers

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);
}|