Introduce sequence_*() access functions

Similarly to tables and indexes, these functions are able to open
relations with a sequence relkind, which is useful to make a distinction
with the other relation kinds.  Previously, commands/sequence.c used a
mix of table_{close,open}() and relation_{close,open}() routines when
manipulating sequence relations, so this clarifies the code.

A direct effect of this change is to align the error messages produced
when attempting DDLs for sequences on relations with an unexpected
relkind, like a table or an index with ALTER SEQUENCE, providing an
extra error detail about the relkind of the relation used in the DDL
query.

Author: Michael Paquier
Reviewed-by: Tomas Vondra
Discussion: https://postgr.es/m/ZWlohtKAs0uVVpZ3@paquier.xyz

1 files changed, 78 insertions, 0 deletions

diff --git a/src/backend/access/sequence/sequence.c b/src/backend/access/sequence/sequence.c
new file mode 100644
index 00000000000..9e30e6e08fe
--- /dev/null
+++ b/src/backend/access/sequence/sequence.c
@@ -0,0 +1,78 @@
+/*-------------------------------------------------------------------------
+ *
+ * sequence.c
+ *	  Generic routines for sequence-related code.
+ *
+ * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/sequence/sequence.c
+ *
+ *
+ * NOTES
+ *	  This file contains sequence_ routines that implement access to sequences
+ *	  (in contrast to other relation types like indexes).
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/relation.h"
+#include "access/sequence.h"
+#include "storage/lmgr.h"
+
+static inline void validate_relation_kind(Relation r);
+
+/* ----------------
+ *		sequence_open - open a sequence relation by relation OID
+ *
+ *		This is essentially relation_open plus check that the relation
+ *		is a sequence.
+ * ----------------
+ */
+Relation
+sequence_open(Oid relationId, LOCKMODE lockmode)
+{
+	Relation	r;
+
+	r = relation_open(relationId, lockmode);
+
+	validate_relation_kind(r);
+
+	return r;
+}
+
+/* ----------------
+ *		sequence_close - close a sequence
+ *
+ *		If lockmode is not "NoLock", we then release the specified lock.
+ *
+ *		Note that it is often sensible to hold a lock beyond relation_close;
+ *		in that case, the lock is released automatically at xact end.
+ * ----------------
+ */
+void
+sequence_close(Relation relation, LOCKMODE lockmode)
+{
+	relation_close(relation, lockmode);
+}
+
+/* ----------------
+ *		validate_relation_kind - check the relation's kind
+ *
+ *		Make sure relkind is from an index
+ * ----------------
+ */
+static inline void
+validate_relation_kind(Relation r)
+{
+	if (r->rd_rel->relkind != RELKIND_SEQUENCE)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("cannot open relation \"%s\"",
+						RelationGetRelationName(r)),
+				 errdetail_relkind_not_supported(r->rd_rel->relkind)));
+}