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/*-------------------------------------------------------------------------
*
* trigfuncs.c
* Builtin functions for useful trigger support.
*
*
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/utils/adt/trigfuncs.c,v 1.6 2009/01/01 17:23:50 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup.h"
#include "commands/trigger.h"
#include "utils/builtins.h"
/*
* suppress_redundant_updates_trigger
*
* This trigger function will inhibit an update from being done
* if the OLD and NEW records are identical.
*/
Datum
suppress_redundant_updates_trigger(PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *) fcinfo->context;
HeapTuple newtuple, oldtuple, rettuple;
HeapTupleHeader newheader, oldheader;
/* make sure it's called as a trigger */
if (!CALLED_AS_TRIGGER(fcinfo))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("suppress_redundant_updates_trigger: must be called as trigger")));
/* and that it's called on update */
if (! TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("suppress_redundant_updates_trigger: must be called on update")));
/* and that it's called before update */
if (! TRIGGER_FIRED_BEFORE(trigdata->tg_event))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("suppress_redundant_updates_trigger: must be called before update")));
/* and that it's called for each row */
if (! TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("suppress_redundant_updates_trigger: must be called for each row")));
/* get tuple data, set default result */
rettuple = newtuple = trigdata->tg_newtuple;
oldtuple = trigdata->tg_trigtuple;
newheader = newtuple->t_data;
oldheader = oldtuple->t_data;
/*
* We are called before the OID, if any, has been transcribed from the
* old tuple to the new (in heap_update). To avoid a bogus compare
* failure, copy the OID now. But check that someone didn't already put
* another OID value into newtuple. (That's not actually possible at
* present, but maybe someday.)
*/
if (trigdata->tg_relation->rd_rel->relhasoids &&
!OidIsValid(HeapTupleHeaderGetOid(newheader)))
HeapTupleHeaderSetOid(newheader, HeapTupleHeaderGetOid(oldheader));
/* if the tuple payload is the same ... */
if (newtuple->t_len == oldtuple->t_len &&
newheader->t_hoff == oldheader->t_hoff &&
(HeapTupleHeaderGetNatts(newheader) ==
HeapTupleHeaderGetNatts(oldheader)) &&
((newheader->t_infomask & ~HEAP_XACT_MASK) ==
(oldheader->t_infomask & ~HEAP_XACT_MASK)) &&
memcmp(((char *)newheader) + offsetof(HeapTupleHeaderData, t_bits),
((char *)oldheader) + offsetof(HeapTupleHeaderData, t_bits),
newtuple->t_len - offsetof(HeapTupleHeaderData, t_bits)) == 0)
{
/* ... then suppress the update */
rettuple = NULL;
}
return PointerGetDatum(rettuple);
}
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