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

src/backend/utils/adt/datum.c

@@ -42,6 +42,8 @@
 
 #include "postgres.h"
 
+#include "access/tuptoaster.h"
+#include "fmgr.h"
 #include "utils/datum.h"
 #include "utils/expandeddatum.h"
 
@@ -251,6 +253,61 @@ datumIsEqual(Datum value1, Datum value2, bool typByVal, int typLen)
 	return res;
 }
 
+/*-------------------------------------------------------------------------
+ * datum_image_eq
+ *
+ * Compares two datums for identical contents, based on byte images.  Return
+ * true if the two datums are equal, false otherwise.
+ *-------------------------------------------------------------------------
+ */
+bool
+datum_image_eq(Datum value1, Datum value2, bool typByVal, int typLen)
+{
+	bool		result = true;
+
+	if (typLen == -1)
+	{
+		Size		len1,
+					len2;
+
+		len1 = toast_raw_datum_size(value1);
+		len2 = toast_raw_datum_size(value2);
+		/* No need to de-toast if lengths don't match. */
+		if (len1 != len2)
+			result = false;
+		else
+		{
+			struct varlena *arg1val;
+			struct varlena *arg2val;
+
+			arg1val = PG_DETOAST_DATUM_PACKED(value1);
+			arg2val = PG_DETOAST_DATUM_PACKED(value2);
+
+			result = (memcmp(VARDATA_ANY(arg1val),
+							 VARDATA_ANY(arg2val),
+							 len1 - VARHDRSZ) == 0);
+
+			/* Only free memory if it's a copy made here. */
+			if ((Pointer) arg1val != (Pointer) value1)
+				pfree(arg1val);
+			if ((Pointer) arg2val != (Pointer) value2)
+				pfree(arg2val);
+		}
+	}
+	else if (typByVal)
+	{
+		result = (value1 == value2);
+	}
+	else
+	{
+		result = (memcmp(DatumGetPointer(value1),
+						 DatumGetPointer(value2),
+						 typLen) == 0);
+	}
+
+	return result;
+}
+
 /*-------------------------------------------------------------------------
  * datumEstimateSpace
  *

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;

src/backend/utils/adt/rowtypes.c

@@ -23,6 +23,7 @@
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
 #include "utils/builtins.h"
+#include "utils/datum.h"
 #include "utils/lsyscache.h"
 #include "utils/typcache.h"
 
@@ -1671,45 +1672,7 @@ record_image_eq(PG_FUNCTION_ARGS)
 			}
 
 			/* Compare the pair of elements */
-			if (att1->attlen == -1)
-			{
-				Size		len1,
-							len2;
-
-				len1 = toast_raw_datum_size(values1[i1]);
-				len2 = toast_raw_datum_size(values2[i2]);
-				/* No need to de-toast if lengths don't match. */
-				if (len1 != len2)
-					result = false;
-				else
-				{
-					struct varlena *arg1val;
-					struct varlena *arg2val;
-
-					arg1val = PG_DETOAST_DATUM_PACKED(values1[i1]);
-					arg2val = PG_DETOAST_DATUM_PACKED(values2[i2]);
-
-					result = (memcmp(VARDATA_ANY(arg1val),
-									 VARDATA_ANY(arg2val),
-									 len1 - VARHDRSZ) == 0);
-
-					/* Only free memory if it's a copy made here. */
-					if ((Pointer) arg1val != (Pointer) values1[i1])
-						pfree(arg1val);
-					if ((Pointer) arg2val != (Pointer) values2[i2])
-						pfree(arg2val);
-				}
-			}
-			else if (att1->attbyval)
-			{
-				result = (values1[i1] == values2[i2]);
-			}
-			else
-			{
-				result = (memcmp(DatumGetPointer(values1[i1]),
-								 DatumGetPointer(values2[i2]),
-								 att1->attlen) == 0);
-			}
+			result = datum_image_eq(values1[i1], values2[i2], att1->attbyval, att2->attlen);
 			if (!result)
 				break;
 		}

src/include/utils/datum.h

@@ -46,6 +46,15 @@ extern Datum datumTransfer(Datum value, bool typByVal, int typLen);
 extern bool datumIsEqual(Datum value1, Datum value2,
 			 bool typByVal, int typLen);
 
+/*
+ * datum_image_eq
+ *
+ * Compares two datums for identical contents, based on byte images.  Return
+ * true if the two datums are equal, false otherwise.
+ */
+extern bool datum_image_eq(Datum value1, Datum value2,
+						   bool typByVal, int typLen);
+
 /*
  * Serialize and restore datums so that we can transfer them to parallel
  * workers.

src/test/regress/expected/foreign_key.out

@@ -1494,6 +1494,40 @@ delete from pktable2 where f1 = 1;
 alter table fktable2 drop constraint fktable2_f1_fkey;
 ERROR:  cannot ALTER TABLE "pktable2" because it has pending trigger events
 commit;
+drop table pktable2, fktable2;
+--
+-- Test keys that "look" different but compare as equal
+--
+create table pktable2 (a float8, b float8, primary key (a, b));
+create table fktable2 (x float8, y float8, foreign key (x, y) references pktable2 (a, b) on update cascade);
+insert into pktable2 values ('-0', '-0');
+insert into fktable2 values ('-0', '-0');
+select * from pktable2;
+ a  | b  
+----+----
+ -0 | -0
+(1 row)
+
+select * from fktable2;
+ x  | y  
+----+----
+ -0 | -0
+(1 row)
+
+update pktable2 set a = '0' where a = '-0';
+select * from pktable2;
+ a | b  
+---+----
+ 0 | -0
+(1 row)
+
+-- should have updated fktable2.x
+select * from fktable2;
+ x | y  
+---+----
+ 0 | -0
+(1 row)
+
 drop table pktable2, fktable2;
 --
 -- Foreign keys and partitioned tables

src/test/regress/sql/foreign_key.sql

@@ -1120,6 +1120,26 @@ commit;
 
 drop table pktable2, fktable2;
 
+--
+-- Test keys that "look" different but compare as equal
+--
+create table pktable2 (a float8, b float8, primary key (a, b));
+create table fktable2 (x float8, y float8, foreign key (x, y) references pktable2 (a, b) on update cascade);
+
+insert into pktable2 values ('-0', '-0');
+insert into fktable2 values ('-0', '-0');
+
+select * from pktable2;
+select * from fktable2;
+
+update pktable2 set a = '0' where a = '-0';
+
+select * from pktable2;
+-- should have updated fktable2.x
+select * from fktable2;
+
+drop table pktable2, fktable2;
+
 
 --
 -- Foreign keys and partitioned tables