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/*-------------------------------------------------------------------------
*
* 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 */
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