| /*------------------------------------------------------------------------- | |
| * | |
| * relfilelocator.h | |
| * Physical access information for relations. | |
| * | |
| * | |
| * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group | |
| * Portions Copyright (c) 1994, Regents of the University of California | |
| * | |
| * src/include/storage/relfilelocator.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; | |
| /* | |
| * 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. | |
| */ | |