1 files changed, 99 insertions, 0 deletions
diff --git a/src/include/storage/relfilelocator.h b/src/include/storage/relfilelocator.h
new file mode 100644
index 00000000000..10f41f3abb3
--- /dev/null
+++ b/src/include/storage/relfilelocator.h
@@ -0,0 +1,99 @@
+/*-------------------------------------------------------------------------
+ *
+ * relfilelocator.h
+ *	  Physical access information for relations.
+ *
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/relfilelocator.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef RELFILELOCATOR_H
+#define RELFILELOCATOR_H
+
+#include "common/relpath.h"
+#include "storage/backendid.h"
+
+/*
+ * RelFileLocator must provide all that we need to know to physically access
+ * a relation, with the exception of the backend ID, which can be provided
+ * separately. Note, however, that a "physical" relation is comprised of
+ * multiple files on the filesystem, as each fork is stored as a separate
+ * file, and each fork can be divided into multiple segments. See md.c.
+ *
+ * spcOid identifies the tablespace of the relation.  It corresponds to
+ * pg_tablespace.oid.
+ *
+ * dbOid identifies the database of the relation.  It is zero for
+ * "shared" relations (those common to all databases of a cluster).
+ * Nonzero dbOid values correspond to pg_database.oid.
+ *
+ * relNumber identifies the specific relation.  relNumber corresponds to
+ * pg_class.relfilenode (NOT pg_class.oid, because we need to be able
+ * to assign new physical files to relations in some situations).
+ * Notice that relNumber is only unique within a database in a particular
+ * tablespace.
+ *
+ * Note: spcOid must be GLOBALTABLESPACE_OID if and only if dbOid is
+ * zero.  We support shared relations only in the "global" tablespace.
+ *
+ * Note: in pg_class we allow reltablespace == 0 to denote that the
+ * relation is stored in its database's "default" tablespace (as
+ * identified by pg_database.dattablespace).  However this shorthand
+ * is NOT allowed in RelFileLocator structs --- the real tablespace ID
+ * must be supplied when setting spcOid.
+ *
+ * Note: in pg_class, relfilenode can be zero to denote that the relation
+ * is a "mapped" relation, whose current true filenode number is available
+ * from relmapper.c.  Again, this case is NOT allowed in RelFileLocators.
+ *
+ * Note: various places use RelFileLocator in hashtable keys.  Therefore,
+ * there *must not* be any unused padding bytes in this struct.  That
+ * should be safe as long as all the fields are of type Oid.
+ */
+typedef struct RelFileLocator
+{
+	Oid			spcOid;			/* tablespace */
+	Oid			dbOid;			/* database */
+	RelFileNumber relNumber;	/* relation */
+} RelFileLocator;
+
+/*
+ * Augmenting a relfilelocator with the backend ID provides all the information
+ * we need to locate the physical storage.  The backend ID is InvalidBackendId
+ * for regular relations (those accessible to more than one backend), or the
+ * owning backend's ID for backend-local relations.  Backend-local relations
+ * are always transient and removed in case of a database crash; they are
+ * never WAL-logged or fsync'd.
+ */
+typedef struct RelFileLocatorBackend
+{
+	RelFileLocator locator;
+	BackendId	backend;
+} RelFileLocatorBackend;
+
+#define RelFileLocatorBackendIsTemp(rlocator) \
+	((rlocator).backend != InvalidBackendId)
+
+/*
+ * Note: RelFileLocatorEquals and RelFileLocatorBackendEquals compare relNumber
+ * first since that is most likely to be different in two unequal
+ * RelFileLocators.  It is probably redundant to compare spcOid if the other
+ * fields are found equal, but do it anyway to be sure.  Likewise for checking
+ * the backend ID in RelFileLocatorBackendEquals.
+ */
+#define RelFileLocatorEquals(locator1, locator2) \
+	((locator1).relNumber == (locator2).relNumber && \
+	 (locator1).dbOid == (locator2).dbOid && \
+	 (locator1).spcOid == (locator2).spcOid)
+
+#define RelFileLocatorBackendEquals(locator1, locator2) \
+	((locator1).locator.relNumber == (locator2).locator.relNumber && \
+	 (locator1).locator.dbOid == (locator2).locator.dbOid && \
+	 (locator1).backend == (locator2).backend && \
+	 (locator1).locator.spcOid == (locator2).locator.spcOid)
+
+#endif							/* RELFILELOCATOR_H */