2 files changed, 78 insertions, 2 deletions
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 5da863d85de..88cb97f445f 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -5911,10 +5911,18 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
 	 * Currently, parallel workers can't access the leader's temporary tables.
 	 * Furthermore, any index predicate or index expressions must be parallel
 	 * safe.
+	 *
+	 * Fetch the list of expressions and predicates directly from the
+	 * catalogs.  Retrieving this information from the relcache would cause
+	 * the expressions and predicates to be flattened, losing properties that
+	 * can be important to check if parallel workers can be used.  For
+	 * example, immutable parallel-unsafe functions, that cannot be used in
+	 * parallel workers, would be changed to Const nodes, that are safe in
+	 * parallel workers.
 	 */
 	if (heap->rd_rel->relpersistence == RELPERSISTENCE_TEMP ||
-		!is_parallel_safe(root, (Node *) RelationGetIndexExpressions(index)) ||
-		!is_parallel_safe(root, (Node *) RelationGetIndexPredicate(index)))
+		!is_parallel_safe(root, (Node *) get_index_expressions(indexOid)) ||
+		!is_parallel_safe(root, (Node *) get_index_predicate(indexOid)))
 	{
 		parallel_workers = 0;
 		goto done;
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 5564b53f257..3c232aa960f 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -3511,6 +3511,74 @@ get_index_column_opclass(Oid index_oid, int attno)
 }
 
 /*
+ * get_index_expressions
+ *
+ *		Given the index OID, its a List of its expressions or NIL if none.
+ */
+List *
+get_index_expressions(Oid index_oid)
+{
+	List	   *result;
+	HeapTuple	tuple;
+	Datum		exprDatum;
+	bool		isnull;
+	char	   *exprString;
+
+	tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(index_oid));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for index %u", index_oid);
+
+	exprDatum = SysCacheGetAttr(INDEXRELID, tuple,
+								Anum_pg_index_indexprs, &isnull);
+	if (isnull)
+	{
+		ReleaseSysCache(tuple);
+		return NIL;
+	}
+
+	exprString = TextDatumGetCString(exprDatum);
+	result = (List *) stringToNode(exprString);
+	pfree(exprString);
+	ReleaseSysCache(tuple);
+
+	return result;
+}
+
+/*
+ * get_index_predicate
+ *
+ *		Given the index OID, return a List of its predicate or NIL if none.
+ */
+List *
+get_index_predicate(Oid index_oid)
+{
+	List	   *result;
+	HeapTuple	tuple;
+	Datum		predDatum;
+	bool		isnull;
+	char	   *predString;
+
+	tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(index_oid));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for index %u", index_oid);
+
+	predDatum = SysCacheGetAttr(INDEXRELID, tuple,
+								Anum_pg_index_indpred, &isnull);
+	if (isnull)
+	{
+		ReleaseSysCache(tuple);
+		return NIL;
+	}
+
+	predString = TextDatumGetCString(predDatum);
+	result = (List *) stringToNode(predString);
+	pfree(predString);
+	ReleaseSysCache(tuple);
+
+	return result;
+}
+
+/*
  * get_index_isreplident
  *
  *		Given the index OID, return pg_index.indisreplident.