1 files changed, 85 insertions, 0 deletions
diff --git a/src/backend/utils/adt/trigfuncs.c b/src/backend/utils/adt/trigfuncs.c
new file mode 100644
index 0000000..cc28cfd
--- /dev/null
+++ b/src/backend/utils/adt/trigfuncs.c
@@ -0,0 +1,85 @@
+/*-------------------------------------------------------------------------
+ *
+ * trigfuncs.c
+ *	  Builtin functions for useful trigger support.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/backend/utils/adt/trigfuncs.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/htup_details.h"
+#include "commands/trigger.h"
+#include "utils/builtins.h"
+#include "utils/rel.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;
+
+	/* 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) + SizeofHeapTupleHeader,
+			   ((char *) oldheader) + SizeofHeapTupleHeader,
+			   newtuple->t_len - SizeofHeapTupleHeader) == 0)
+	{
+		/* ... then suppress the update */
+		rettuple = NULL;
+	}
+
+	return PointerGetDatum(rettuple);
+}