对PostgreSQL中 pg_各表的RelationId的认识

/* ----------------
 *        heap_open - open a heap relation by relation OID
 *
 *        This is essentially relation_open plus check that the relation
 *        is not an index nor a composite type.  (The caller should also
 *        check that it's not a view or foreign table before assuming it has
 *        storage.)
 * ----------------
 */
Relation
heap_open(Oid relationId, LOCKMODE lockmode)
{
    //fprintf(stderr,"++++++++++++++++++++ In heap_open start by process %d....relationId is:%d\n",

getpid(),relationId);
    Relation    r;

    r = relation_open(relationId, lockmode);

    if (r->rd_rel->relkind == RELKIND_INDEX)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is an index",
                        RelationGetRelationName(r))));
    else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is a composite type",
                        RelationGetRelationName(r))));

    //fprintf(stderr,"++++++++++++++++++++ In heap_open end by process %d\n\n",getpid());

    return r;
}

/* ----------------
 *        relation_open - open any relation by relation OID
 *
 *        If lockmode is not "NoLock", the specified kind of lock is
 *        obtained on the relation.  (Generally, NoLock should only be
 *        used if the caller knows it has some appropriate lock on the
 *        relation already.)
 *
 *        An error is raised if the relation does not exist.
 *
 *        NB: a "relation" is anything with a pg_class entry.  The caller is
 *        expected to check whether the relkind is something it can handle.
 * ----------------
 */
Relation
relation_open(Oid relationId, LOCKMODE lockmode)
{

    fprintf(stderr,"___________________ In relation_open start by process %d\n",getpid());

    Relation    r;

    Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);

    /* Get the lock before trying to open the relcache entry */
    if (lockmode != NoLock)
        LockRelationOid(relationId, lockmode);

    /* The relcache does all the real work... */
    r = RelationIdGetRelation(relationId);

    fprintf(stderr,"In relation_open ,the relNode is:%d....\n\n",r->rd_node.relNode);

    if (!RelationIsValid(r))
        elog(ERROR, "could not open relation with OID %u", relationId);

    /* Make note that we've accessed a temporary relation */
    if (RelationUsesLocalBuffers(r))
        MyXactAccessedTempRel = true;

    pgstat_initstats(r);

    fprintf(stderr,"___________________ In relation_open end by process %d\n",getpid());

    return r;
}