1 files changed, 151 insertions, 2 deletions

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index c958758df62..8d2ad018bbf 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -1049,6 +1049,10 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 	else
 		relation->rd_rsdesc = NULL;
 
+	/* foreign key data is not loaded till asked for */
+	relation->rd_fkeylist = NIL;
+	relation->rd_fkeyvalid = false;
+
 	/*
 	 * if it's an index, initialize index-related information
 	 */
@@ -2030,11 +2034,12 @@ RelationDestroyRelation(Relation relation, bool remember_tupdesc)
 		else
 			FreeTupleDesc(relation->rd_att);
 	}
+	FreeTriggerDesc(relation->trigdesc);
+	list_free_deep(relation->rd_fkeylist);
 	list_free(relation->rd_indexlist);
 	bms_free(relation->rd_indexattr);
 	bms_free(relation->rd_keyattr);
 	bms_free(relation->rd_idattr);
-	FreeTriggerDesc(relation->trigdesc);
 	if (relation->rd_options)
 		pfree(relation->rd_options);
 	if (relation->rd_indextuple)
@@ -3804,6 +3809,147 @@ CheckConstraintCmp(const void *a, const void *b)
 }
 
 /*
+ * RelationGetFKeyList -- get a list of foreign key info for the relation
+ *
+ * Returns a list of ForeignKeyCacheInfo structs, one per FK constraining
+ * the given relation.  This data is a direct copy of relevant fields from
+ * pg_constraint.  The list items are in no particular order.
+ *
+ * CAUTION: the returned list is part of the relcache's data, and could
+ * vanish in a relcache entry reset.  Callers must inspect or copy it
+ * before doing anything that might trigger a cache flush, such as
+ * system catalog accesses.  copyObject() can be used if desired.
+ * (We define it this way because current callers want to filter and
+ * modify the list entries anyway, so copying would be a waste of time.)
+ */
+List *
+RelationGetFKeyList(Relation relation)
+{
+	List	   *result;
+	Relation	conrel;
+	SysScanDesc conscan;
+	ScanKeyData skey;
+	HeapTuple	htup;
+	List	   *oldlist;
+	MemoryContext oldcxt;
+
+	/* Quick exit if we already computed the list. */
+	if (relation->rd_fkeyvalid)
+		return relation->rd_fkeylist;
+
+	/* Fast path: if it doesn't have any triggers, it can't have FKs */
+	if (!relation->rd_rel->relhastriggers)
+		return NIL;
+
+	/*
+	 * We build the list we intend to return (in the caller's context) while
+	 * doing the scan.  After successfully completing the scan, we copy that
+	 * list into the relcache entry.  This avoids cache-context memory leakage
+	 * if we get some sort of error partway through.
+	 */
+	result = NIL;
+
+	/* Prepare to scan pg_constraint for entries having conrelid = this rel. */
+	ScanKeyInit(&skey,
+				Anum_pg_constraint_conrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationGetRelid(relation)));
+
+	conrel = heap_open(ConstraintRelationId, AccessShareLock);
+	conscan = systable_beginscan(conrel, ConstraintRelidIndexId, true,
+								 NULL, 1, &skey);
+
+	while (HeapTupleIsValid(htup = systable_getnext(conscan)))
+	{
+		Form_pg_constraint constraint = (Form_pg_constraint) GETSTRUCT(htup);
+		ForeignKeyCacheInfo *info;
+		Datum		adatum;
+		bool		isnull;
+		ArrayType  *arr;
+		int			nelem;
+
+		/* consider only foreign keys */
+		if (constraint->contype != CONSTRAINT_FOREIGN)
+			continue;
+
+		info = makeNode(ForeignKeyCacheInfo);
+		info->conrelid = constraint->conrelid;
+		info->confrelid = constraint->confrelid;
+
+		/* Extract data from conkey field */
+		adatum = fastgetattr(htup, Anum_pg_constraint_conkey,
+							 conrel->rd_att, &isnull);
+		if (isnull)
+			elog(ERROR, "null conkey for rel %s",
+				 RelationGetRelationName(relation));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelem = ARR_DIMS(arr)[0];
+		if (ARR_NDIM(arr) != 1 ||
+			nelem < 1 ||
+			nelem > INDEX_MAX_KEYS ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "conkey is not a 1-D smallint array");
+
+		info->nkeys = nelem;
+		memcpy(info->conkey, ARR_DATA_PTR(arr), nelem * sizeof(AttrNumber));
+
+		/* Likewise for confkey */
+		adatum = fastgetattr(htup, Anum_pg_constraint_confkey,
+							 conrel->rd_att, &isnull);
+		if (isnull)
+			elog(ERROR, "null confkey for rel %s",
+				 RelationGetRelationName(relation));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelem = ARR_DIMS(arr)[0];
+		if (ARR_NDIM(arr) != 1 ||
+			nelem != info->nkeys ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != INT2OID)
+			elog(ERROR, "confkey is not a 1-D smallint array");
+
+		memcpy(info->confkey, ARR_DATA_PTR(arr), nelem * sizeof(AttrNumber));
+
+		/* Likewise for conpfeqop */
+		adatum = fastgetattr(htup, Anum_pg_constraint_conpfeqop,
+							 conrel->rd_att, &isnull);
+		if (isnull)
+			elog(ERROR, "null conpfeqop for rel %s",
+				 RelationGetRelationName(relation));
+
+		arr = DatumGetArrayTypeP(adatum);		/* ensure not toasted */
+		nelem = ARR_DIMS(arr)[0];
+		if (ARR_NDIM(arr) != 1 ||
+			nelem != info->nkeys ||
+			ARR_HASNULL(arr) ||
+			ARR_ELEMTYPE(arr) != OIDOID)
+			elog(ERROR, "conpfeqop is not a 1-D OID array");
+
+		memcpy(info->conpfeqop, ARR_DATA_PTR(arr), nelem * sizeof(Oid));
+
+		/* Add FK's node to the result list */
+		result = lappend(result, info);
+	}
+
+	systable_endscan(conscan);
+	heap_close(conrel, AccessShareLock);
+
+	/* Now save a copy of the completed list in the relcache entry. */
+	oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
+	oldlist = relation->rd_fkeylist;
+	relation->rd_fkeylist = copyObject(result);
+	relation->rd_fkeyvalid = true;
+	MemoryContextSwitchTo(oldcxt);
+
+	/* Don't leak the old list, if there is one */
+	list_free_deep(oldlist);
+
+	return result;
+}
+
+/*
  * RelationGetIndexList -- get a list of OIDs of indexes on this relation
  *
  * The index list is created only if someone requests it.  We scan pg_index
@@ -4892,7 +5038,8 @@ load_relcache_init_file(bool shared)
 		 * format is complex and subject to change).  They must be rebuilt if
 		 * needed by RelationCacheInitializePhase3.  This is not expected to
 		 * be a big performance hit since few system catalogs have such. Ditto
-		 * for index expressions, predicates, exclusion info, and FDW info.
+		 * for RLS policy data, index expressions, predicates, exclusion info,
+		 * and FDW info.
 		 */
 		rel->rd_rules = NULL;
 		rel->rd_rulescxt = NULL;
@@ -4914,6 +5061,8 @@ load_relcache_init_file(bool shared)
 		else
 			rel->rd_refcnt = 0;
 		rel->rd_indexvalid = 0;
+		rel->rd_fkeylist = NIL;
+		rel->rd_fkeyvalid = false;
 		rel->rd_indexlist = NIL;
 		rel->rd_oidindex = InvalidOid;
 		rel->rd_replidindex = InvalidOid;