101 lines
4.0 KiB
C
101 lines
4.0 KiB
C
/*-------------------------------------------------------------------------
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*
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* relfilelocator.h
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* Physical access information for relations.
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*
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*
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* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/relfilelocator.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef RELFILELOCATOR_H
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#define RELFILELOCATOR_H
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#include "common/relpath.h"
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#include "storage/procnumber.h"
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/*
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* RelFileLocator must provide all that we need to know to physically access
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* a relation, with the exception of the backend's proc number, which can be
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* provided separately. Note, however, that a "physical" relation is
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* comprised of multiple files on the filesystem, as each fork is stored as
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* a separate file, and each fork can be divided into multiple segments. See
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* md.c.
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*
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* spcOid identifies the tablespace of the relation. It corresponds to
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* pg_tablespace.oid.
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*
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* dbOid identifies the database of the relation. It is zero for
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* "shared" relations (those common to all databases of a cluster).
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* Nonzero dbOid values correspond to pg_database.oid.
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*
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* relNumber identifies the specific relation. relNumber corresponds to
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* pg_class.relfilenode (NOT pg_class.oid, because we need to be able
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* to assign new physical files to relations in some situations).
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* Notice that relNumber is only unique within a database in a particular
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* tablespace.
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*
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* Note: spcOid must be GLOBALTABLESPACE_OID if and only if dbOid is
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* zero. We support shared relations only in the "global" tablespace.
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*
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* Note: in pg_class we allow reltablespace == 0 to denote that the
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* relation is stored in its database's "default" tablespace (as
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* identified by pg_database.dattablespace). However this shorthand
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* is NOT allowed in RelFileLocator structs --- the real tablespace ID
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* must be supplied when setting spcOid.
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*
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* Note: in pg_class, relfilenode can be zero to denote that the relation
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* is a "mapped" relation, whose current true filenode number is available
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* from relmapper.c. Again, this case is NOT allowed in RelFileLocators.
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*
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* Note: various places use RelFileLocator in hashtable keys. Therefore,
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* there *must not* be any unused padding bytes in this struct. That
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* should be safe as long as all the fields are of type Oid.
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*/
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typedef struct RelFileLocator
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{
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Oid spcOid; /* tablespace */
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Oid dbOid; /* database */
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RelFileNumber relNumber; /* relation */
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} RelFileLocator;
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/*
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* Augmenting a relfilelocator with the backend's proc number provides all the
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* information we need to locate the physical storage. 'backend' is
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* INVALID_PROC_NUMBER for regular relations (those accessible to more than
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* one backend), or the owning backend's proc number for backend-local
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* relations. Backend-local relations are always transient and removed in
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* case of a database crash; they are never WAL-logged or fsync'd.
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*/
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typedef struct RelFileLocatorBackend
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{
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RelFileLocator locator;
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ProcNumber backend;
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} RelFileLocatorBackend;
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#define RelFileLocatorBackendIsTemp(rlocator) \
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((rlocator).backend != INVALID_PROC_NUMBER)
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/*
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* Note: RelFileLocatorEquals and RelFileLocatorBackendEquals compare relNumber
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* first since that is most likely to be different in two unequal
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* RelFileLocators. It is probably redundant to compare spcOid if the other
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* fields are found equal, but do it anyway to be sure. Likewise for checking
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* the backend number in RelFileLocatorBackendEquals.
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*/
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#define RelFileLocatorEquals(locator1, locator2) \
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((locator1).relNumber == (locator2).relNumber && \
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(locator1).dbOid == (locator2).dbOid && \
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(locator1).spcOid == (locator2).spcOid)
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#define RelFileLocatorBackendEquals(locator1, locator2) \
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((locator1).locator.relNumber == (locator2).locator.relNumber && \
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(locator1).locator.dbOid == (locator2).locator.dbOid && \
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(locator1).backend == (locator2).backend && \
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(locator1).locator.spcOid == (locator2).locator.spcOid)
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#endif /* RELFILELOCATOR_H */
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