suppress_redundant_updates_trigger function.

1 files changed, 77 insertions, 0 deletions

diff --git a/src/backend/utils/adt/trigfuncs.c b/src/backend/utils/adt/trigfuncs.c
new file mode 100644
index 00000000000..2f3692ec431
--- /dev/null
+++ b/src/backend/utils/adt/trigfuncs.c
@@ -0,0 +1,77 @@
+/*-------------------------------------------------------------------------
+ *
+ * trigfuncs.c
+ *    Builtin functions for useful trigger support.
+ *
+ *
+ * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * $PostgreSQL: pgsql/src/backend/utils/adt/trigfuncs.c,v 1.1 2008/11/03 20:17:20 adunstan Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+
+
+
+#include "postgres.h"
+#include "commands/trigger.h"
+#include "access/htup.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))
+        elog(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: may only 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: may only 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: may only be called for each row")));
+
+	/* get tuple data, set default return */
+	rettuple  = newtuple = trigdata->tg_newtuple;
+	oldtuple = trigdata->tg_trigtuple;
+
+	newheader = newtuple->t_data;
+	oldheader = oldtuple->t_data;
+
+    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)
+	{
+		rettuple = NULL;
+	}
+	
+    return PointerGetDatum(rettuple);
+}