Fix bogus test for hypothetical indexes in get_actual_variable_range().

That function was supposing that indexoid == 0 for a hypothetical index,
but that is not likely to be true in any non-toy implementation of an index
adviser, since assigning a fake OID is the only way to know at EXPLAIN time
which hypothetical index got selected.  Fix by adding a flag to
IndexOptInfo to mark hypothetical indexes.  Back-patch to 9.0 where
get_actual_variable_range() was added.

Gurjeet Singh

src/backend/nodes/outfuncs.c

@@ -1700,10 +1700,12 @@ _outIndexOptInfo(StringInfo str, IndexOptInfo *node)
 	WRITE_UINT_FIELD(pages);
 	WRITE_FLOAT_FIELD(tuples, "%.0f");
 	WRITE_INT_FIELD(ncolumns);
+	WRITE_OID_FIELD(relam);
 	WRITE_NODE_FIELD(indexprs);
 	WRITE_NODE_FIELD(indpred);
 	WRITE_BOOL_FIELD(predOK);
 	WRITE_BOOL_FIELD(unique);
+	WRITE_BOOL_FIELD(hypothetical);
 }
 
 static void

src/backend/optimizer/util/plancat.c

@@ -316,6 +316,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 				ChangeVarNodes((Node *) info->indpred, 1, varno, 0);
 			info->predOK = false;		/* set later in indxpath.c */
 			info->unique = index->indisunique;
+			info->hypothetical = false;
 
 			/*
 			 * Estimate the index size.  If it's not a partial index, we lock

src/backend/utils/adt/selfuncs.c

@@ -4562,10 +4562,10 @@ get_actual_variable_range(PlannerInfo *root, VariableStatData *vardata,
 			continue;
 
 		/*
-		 * The index list might include fictitious indexes inserted by a
+		 * The index list might include hypothetical indexes inserted by a
 		 * get_relation_info hook --- don't try to access them.
 		 */
-		if (!OidIsValid(index->indexoid))
+		if (index->hypothetical)
 			continue;
 
 		/*

src/include/nodes/relation.h

@@ -455,7 +455,7 @@ typedef struct IndexOptInfo
 	int			ncolumns;		/* number of columns in index */
 	Oid		   *opfamily;		/* OIDs of operator families for columns */
 	int		   *indexkeys;		/* column numbers of index's keys, or 0 */
-	Oid		   *indexcollations;/* OIDs of the collations of the index columns */
+	Oid		   *indexcollations;	/* OIDs of collations of index columns */
 	Oid		   *opcintype;		/* OIDs of opclass declared input data types */
 	Oid		   *sortopfamily;	/* OIDs of btree opfamilies, if orderable */
 	bool	   *reverse_sort;	/* is sort order descending? */
@@ -469,6 +469,7 @@ typedef struct IndexOptInfo
 
 	bool		predOK;			/* true if predicate matches query */
 	bool		unique;			/* true if a unique index */
+	bool		hypothetical;	/* true if index doesn't really exist */
 	bool		amcanorderbyop;	/* does AM support order by operator result? */
 	bool		amoptionalkey;	/* can query omit key for the first column? */
 	bool		amsearchnulls;	/* can AM search for NULL/NOT NULL entries? */