1/*-------------------------------------------------------------------------
2 *
3 * relfilenode.h
4 * Physical access information for relations.
5 *
6 *
7 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
9 *
10 * src/include/storage/relfilenode.h
11 *
12 *-------------------------------------------------------------------------
13 */
14#ifndef RELFILENODE_H
15#define RELFILENODE_H
16
17#include "common/relpath.h"
18#include "storage/backendid.h"
19
20/*
21 * RelFileNode must provide all that we need to know to physically access
22 * a relation, with the exception of the backend ID, which can be provided
23 * separately. Note, however, that a "physical" relation is comprised of
24 * multiple files on the filesystem, as each fork is stored as a separate
25 * file, and each fork can be divided into multiple segments. See md.c.
26 *
27 * spcNode identifies the tablespace of the relation. It corresponds to
28 * pg_tablespace.oid.
29 *
30 * dbNode identifies the database of the relation. It is zero for
31 * "shared" relations (those common to all databases of a cluster).
32 * Nonzero dbNode values correspond to pg_database.oid.
33 *
34 * relNode identifies the specific relation. relNode corresponds to
35 * pg_class.relfilenode (NOT pg_class.oid, because we need to be able
36 * to assign new physical files to relations in some situations).
37 * Notice that relNode is only unique within a database in a particular
38 * tablespace.
39 *
40 * Note: spcNode must be GLOBALTABLESPACE_OID if and only if dbNode is
41 * zero. We support shared relations only in the "global" tablespace.
42 *
43 * Note: in pg_class we allow reltablespace == 0 to denote that the
44 * relation is stored in its database's "default" tablespace (as
45 * identified by pg_database.dattablespace). However this shorthand
46 * is NOT allowed in RelFileNode structs --- the real tablespace ID
47 * must be supplied when setting spcNode.
48 *
49 * Note: in pg_class, relfilenode can be zero to denote that the relation
50 * is a "mapped" relation, whose current true filenode number is available
51 * from relmapper.c. Again, this case is NOT allowed in RelFileNodes.
52 *
53 * Note: various places use RelFileNode in hashtable keys. Therefore,
54 * there *must not* be any unused padding bytes in this struct. That
55 * should be safe as long as all the fields are of type Oid.
56 */
57typedef struct RelFileNode
58{
59 Oid spcNode; /* tablespace */
60 Oid dbNode; /* database */
61 Oid relNode; /* relation */
62} RelFileNode;
63
64/*
65 * Augmenting a relfilenode with the backend ID provides all the information
66 * we need to locate the physical storage. The backend ID is InvalidBackendId
67 * for regular relations (those accessible to more than one backend), or the
68 * owning backend's ID for backend-local relations. Backend-local relations
69 * are always transient and removed in case of a database crash; they are
70 * never WAL-logged or fsync'd.
71 */
72typedef struct RelFileNodeBackend
73{
74 RelFileNode node;
75 BackendId backend;
76} RelFileNodeBackend;
77
78#define RelFileNodeBackendIsTemp(rnode) \
79 ((rnode).backend != InvalidBackendId)
80
81/*
82 * Note: RelFileNodeEquals and RelFileNodeBackendEquals compare relNode first
83 * since that is most likely to be different in two unequal RelFileNodes. It
84 * is probably redundant to compare spcNode if the other fields are found equal,
85 * but do it anyway to be sure. Likewise for checking the backend ID in
86 * RelFileNodeBackendEquals.
87 */
88#define RelFileNodeEquals(node1, node2) \
89 ((node1).relNode == (node2).relNode && \
90 (node1).dbNode == (node2).dbNode && \
91 (node1).spcNode == (node2).spcNode)
92
93#define RelFileNodeBackendEquals(node1, node2) \
94 ((node1).node.relNode == (node2).node.relNode && \
95 (node1).node.dbNode == (node2).node.dbNode && \
96 (node1).backend == (node2).backend && \
97 (node1).node.spcNode == (node2).node.spcNode)
98
99#endif /* RELFILENODE_H */
100