Fix optimization of foreign-key on update actions

In RI_FKey_pk_upd_check_required(), we check among other things
whether the old and new key are equal, so that we don't need to run
cascade actions when nothing has actually changed.  This was using the
equality operator.  But the effect of this is that if a value in the
primary key is changed to one that "looks" different but compares as
equal, the update is not propagated.  (Examples are float -0 and 0 and
case-insensitive text.)  This appears to violate the SQL standard, and
it also behaves inconsistently if in a multicolumn key another key is
also updated that would cause the row to compare as not equal.

To fix, if we are looking at the PK table in ri_KeysEqual(), then do a
bytewise comparison similar to record_image_eq() instead of using the
equality operators.  This only makes a difference for ON UPDATE
CASCADE, but for consistency we treat all changes to the PK the same.  For
the FK table, we continue to use the equality operators.

Discussion: https://www.postgresql.org/message-id/flat/3326fc2e-bc02-d4c5-e3e5-e54da466e89a@2ndquadrant.com

1 files changed, 27 insertions, 13 deletions

diff --git a/src/backend/utils/adt/ri_triggers.c b/src/backend/utils/adt/ri_triggers.c
index d715709b7cd..b4d0029877b 100644
--- a/src/backend/utils/adt/ri_triggers.c
+++ b/src/backend/utils/adt/ri_triggers.c
@@ -42,6 +42,7 @@
 #include "storage/bufmgr.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
+#include "utils/datum.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
 #include "utils/inval.h"
@@ -2402,18 +2403,11 @@ ri_KeysEqual(Relation rel, TupleTableSlot *oldslot, TupleTableSlot *newslot,
 			 const RI_ConstraintInfo *riinfo, bool rel_is_pk)
 {
 	const int16 *attnums;
-	const Oid  *eq_oprs;
 
 	if (rel_is_pk)
-	{
 		attnums = riinfo->pk_attnums;
-		eq_oprs = riinfo->pp_eq_oprs;
-	}
 	else
-	{
 		attnums = riinfo->fk_attnums;
-		eq_oprs = riinfo->ff_eq_oprs;
-	}
 
 	/* XXX: could be worthwhile to fetch all necessary attrs at once */
 	for (int i = 0; i < riinfo->nkeys; i++)
@@ -2436,12 +2430,32 @@ ri_KeysEqual(Relation rel, TupleTableSlot *oldslot, TupleTableSlot *newslot,
 		if (isnull)
 			return false;
 
-		/*
-		 * Compare them with the appropriate equality operator.
-		 */
-		if (!ri_AttributesEqual(eq_oprs[i], RIAttType(rel, attnums[i]),
-								oldvalue, newvalue))
-			return false;
+		if (rel_is_pk)
+		{
+			/*
+			 * If we are looking at the PK table, then do a bytewise
+			 * comparison.  We must propagate PK changes if the value is
+			 * changed to one that "looks" different but would compare as
+			 * equal using the equality operator.  This only makes a
+			 * difference for ON UPDATE CASCADE, but for consistency we treat
+			 * all changes to the PK the same.
+			 */
+			Form_pg_attribute att = TupleDescAttr(oldslot->tts_tupleDescriptor, attnums[i] - 1);
+
+			if (!datum_image_eq(oldvalue, newvalue, att->attbyval, att->attlen))
+				return false;
+		}
+		else
+		{
+			/*
+			 * For the FK table, compare with the appropriate equality
+			 * operator.  Changes that compare equal will still satisfy the
+			 * constraint after the update.
+			 */
+			if (!ri_AttributesEqual(riinfo->ff_eq_oprs[i], RIAttType(rel, attnums[i]),
+									oldvalue, newvalue))
+				return false;
+		}
 	}
 
 	return true;