Load FK defs into relcache for use by planner

Fastpath ignores this if no triggers defined.

Author: Tomas Vondra, with fastpath and comments added by me
Reviewers: David Rowley, Simon Riggs

src/backend/nodes/outfuncs.c

@@ -2137,6 +2137,16 @@ _outIndexOptInfo(StringInfo str, const IndexOptInfo *node)
 	/* we don't bother with fields copied from the index AM's API struct */
 }
 
+static void
+_outForeignKeyOptInfo(StringInfo str, const ForeignKeyOptInfo *node)
+{
+	WRITE_NODE_TYPE("FOREIGNKEYOPTINFO");
+
+	WRITE_OID_FIELD(conrelid);
+	WRITE_OID_FIELD(confrelid);
+	WRITE_INT_FIELD(nkeys);
+}
+
 static void
 _outEquivalenceClass(StringInfo str, const EquivalenceClass *node)
 {
@@ -3607,6 +3617,9 @@ _outNode(StringInfo str, const void *obj)
 			case T_IndexOptInfo:
 				_outIndexOptInfo(str, obj);
 				break;
+			case T_ForeignKeyOptInfo:
+				_outForeignKeyOptInfo(str, obj);
+				break;
 			case T_EquivalenceClass:
 				_outEquivalenceClass(str, obj);
 				break;

src/backend/optimizer/util/plancat.c

@@ -28,6 +28,7 @@
 #include "catalog/dependency.h"
 #include "catalog/heap.h"
 #include "catalog/pg_am.h"
+#include "catalog/pg_constraint.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -41,6 +42,7 @@
 #include "rewrite/rewriteManip.h"
 #include "storage/bufmgr.h"
 #include "utils/lsyscache.h"
+#include "utils/syscache.h"
 #include "utils/rel.h"
 #include "utils/snapmgr.h"
 
@@ -94,6 +96,9 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 	Relation	relation;
 	bool		hasindex;
 	List	   *indexinfos = NIL;
+	List	   *fkinfos = NIL;
+	List	   *fkoidlist;
+	ListCell   *l;
 
 	/*
 	 * We need not lock the relation since it was already locked, either by
@@ -141,7 +146,6 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 	if (hasindex)
 	{
 		List	   *indexoidlist;
-		ListCell   *l;
 		LOCKMODE	lmode;
 
 		indexoidlist = RelationGetIndexList(relation);
@@ -388,6 +392,85 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 
 	rel->indexlist = indexinfos;
 
+	/*
+	 * Load foreign key data. Note this is the definitional data from the
+	 * catalog only and does not lock the referenced tables here. The
+	 * precise definition of the FK is important and may affect the usage
+	 * elsewhere in the planner, e.g. if the constraint is deferred or
+	 * if the constraint is not valid then relying upon this in the executor
+	 * may not be accurate, though might be considered a useful estimate for
+	 * planning purposes.
+	 */
+	fkoidlist = RelationGetFKeyList(relation);
+
+	foreach(l, fkoidlist)
+	{
+		int			i;
+		ArrayType  *arr;
+		Datum		adatum;
+		bool		isnull;
+		int			numkeys;
+		Oid			fkoid = lfirst_oid(l);
+
+		HeapTuple	htup = SearchSysCache1(CONSTROID, ObjectIdGetDatum(fkoid));
+		Form_pg_constraint constraint = (Form_pg_constraint) GETSTRUCT(htup);
+
+		ForeignKeyOptInfo *info;
+
+		Assert(constraint->contype == CONSTRAINT_FOREIGN);
+
+		info = makeNode(ForeignKeyOptInfo);
+
+		info->conrelid = constraint->conrelid;
+		info->confrelid = constraint->confrelid;
+
+		/* conkey */
+		adatum = SysCacheGetAttr(CONSTROID, htup,
+									Anum_pg_constraint_conkey, &isnull);
+		Assert(!isnull);
+
+		arr = DatumGetArrayTypeP(adatum);
+		numkeys = ARR_DIMS(arr)[0];
+		info->conkeys = (int*)palloc0(numkeys * sizeof(int));
+
+		for (i = 0; i < numkeys; i++)
+			info->conkeys[i] = ((int16 *) ARR_DATA_PTR(arr))[i];
+
+		/* confkey */
+		adatum = SysCacheGetAttr(CONSTROID, htup,
+									Anum_pg_constraint_confkey, &isnull);
+		Assert(!isnull);
+
+		arr = DatumGetArrayTypeP(adatum);
+		numkeys = ARR_DIMS(arr)[0];
+		info->confkeys = (int*)palloc0(numkeys * sizeof(int));
+
+		for (i = 0; i < numkeys; i++)
+			info->confkeys[i] = ((int16 *) ARR_DATA_PTR(arr))[i];
+
+		/* conpfeqop */
+		adatum = SysCacheGetAttr(CONSTROID, htup,
+									Anum_pg_constraint_conpfeqop, &isnull);
+		Assert(!isnull);
+
+		arr = DatumGetArrayTypeP(adatum);
+		numkeys = ARR_DIMS(arr)[0];
+		info->conpfeqop = (Oid*)palloc0(numkeys * sizeof(Oid));
+
+		for (i = 0; i < numkeys; i++)
+			info->conpfeqop[i] = ((Oid *) ARR_DATA_PTR(arr))[i];
+
+		info->nkeys = numkeys;
+
+		ReleaseSysCache(htup);
+
+		fkinfos = lcons(info, fkinfos);
+	}
+
+	list_free(fkoidlist);
+
+	rel->fkeylist = fkinfos;
+
 	/* Grab foreign-table info using the relcache, while we have it */
 	if (relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
 	{

src/backend/utils/cache/relcache.c

@@ -2031,6 +2031,7 @@ RelationDestroyRelation(Relation relation, bool remember_tupdesc)
 			FreeTupleDesc(relation->rd_att);
 	}
 	list_free(relation->rd_indexlist);
+	list_free(relation->rd_fkeylist);
 	bms_free(relation->rd_indexattr);
 	bms_free(relation->rd_keyattr);
 	bms_free(relation->rd_idattr);
@@ -3956,6 +3957,79 @@ RelationGetIndexList(Relation relation)
 	return result;
 }
 
+/*
+ * RelationGetFKeyList -- get a list of foreign key oids
+ *
+ * Use an index scan on pg_constraint to load in FK definitions,
+ * intended for use within the planner, not for enforcing FKs.
+ *
+ * Data is ordered by Oid, though this is not critical at this point
+ * since we do not lock the referenced relations.
+ */
+List *
+RelationGetFKeyList(Relation relation)
+{
+	Relation	conrel;
+	SysScanDesc conscan;
+	ScanKeyData skey;
+	HeapTuple	htup;
+	List	   *result;
+	List	   *oldlist;
+	MemoryContext oldcxt;
+
+	/* Quick exit if we already computed the list. */
+	if (relation->rd_fkeylist)
+		return list_copy(relation->rd_fkeylist);
+
+	/* Fast path if no FKs... if it doesn't have a trigger, it can't have a FK */
+	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);
+
+		/* return only foreign keys */
+		if (constraint->contype != CONSTRAINT_FOREIGN)
+			continue;
+
+		/* Add FK's OID to result list in the proper order */
+		result = insert_ordered_oid(result, HeapTupleGetOid(htup));
+	}
+
+	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 = list_copy(result);
+	MemoryContextSwitchTo(oldcxt);
+
+	/* Don't leak the old list, if there is one */
+	list_free(oldlist);
+
+	return result;
+}
+
 /*
  * insert_ordered_oid
  *		Insert a new Oid into a sorted list of Oids, preserving ordering
@@ -4920,6 +4994,7 @@ load_relcache_init_file(bool shared)
 		rel->rd_indexattr = NULL;
 		rel->rd_keyattr = NULL;
 		rel->rd_idattr = NULL;
+		rel->rd_fkeylist = NIL;
 		rel->rd_createSubid = InvalidSubTransactionId;
 		rel->rd_newRelfilenodeSubid = InvalidSubTransactionId;
 		rel->rd_amcache = NULL;

src/include/nodes/nodes.h

@@ -223,6 +223,7 @@ typedef enum NodeTag
 	T_PlannerGlobal,
 	T_RelOptInfo,
 	T_IndexOptInfo,
+	T_ForeignKeyOptInfo,
 	T_ParamPathInfo,
 	T_Path,
 	T_IndexPath,

src/include/nodes/relation.h

@@ -516,6 +516,7 @@ typedef struct RelOptInfo
 	List	   *lateral_vars;	/* LATERAL Vars and PHVs referenced by rel */
 	Relids		lateral_referencers;	/* rels that reference me laterally */
 	List	   *indexlist;		/* list of IndexOptInfo */
+	List	   *fkeylist;			/* list of ForeignKeyOptInfo */
 	BlockNumber pages;			/* size estimates derived from pg_class */
 	double		tuples;
 	double		allvisfrac;
@@ -621,6 +622,27 @@ typedef struct IndexOptInfo
 	void		(*amcostestimate) ();	/* AM's cost estimator */
 } IndexOptInfo;
 
+/*
+ * ForeignKeyOptInfo
+ *		Per-foreign-key information for planning/optimization
+ *
+ * Only includes columns from pg_constraint related to foreign keys.
+ *
+ * conkeys[], confkeys[] and conpfeqop[] each have nkeys entries.
+ */
+typedef struct ForeignKeyOptInfo
+{
+	NodeTag		type;
+
+	Oid			conrelid;	/* relation constrained by the foreign key */
+	Oid			confrelid;	/* relation referenced by the foreign key */
+
+	int			nkeys;		/* number of columns in the foreign key */
+	int		   *conkeys;	/* attnums of columns in the constrained table */
+	int		   *confkeys;	/* attnums of columns in the referenced table */
+	Oid		   *conpfeqop;	/* OIDs of equality operators used by the FK */
+
+} ForeignKeyOptInfo;
 
 /*
  * EquivalenceClasses

src/include/utils/rel.h

@@ -94,6 +94,9 @@ typedef struct RelationData
 	Oid			rd_oidindex;	/* OID of unique index on OID, if any */
 	Oid			rd_replidindex; /* OID of replica identity index, if any */
 
+	/* data managed by RelationGetFKList: */
+	List	   *rd_fkeylist;		/* OIDs of foreign keys */
+
 	/* data managed by RelationGetIndexAttrBitmap: */
 	Bitmapset  *rd_indexattr;	/* identifies columns used in indexes */
 	Bitmapset  *rd_keyattr;		/* cols that can be ref'd by foreign keys */

src/include/utils/relcache.h

@@ -38,6 +38,7 @@ extern void RelationClose(Relation relation);
  * Routines to compute/retrieve additional cached information
  */
 extern List *RelationGetIndexList(Relation relation);
+extern List *RelationGetFKeyList(Relation relation);
 extern Oid	RelationGetOidIndex(Relation relation);
 extern Oid	RelationGetReplicaIndex(Relation relation);
 extern List *RelationGetIndexExpressions(Relation relation);