relcache.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

	/*
	 * first try and get a reldesc from the cache
	 */
	rd = RelationIdCacheGetRelation(relationId);
	if (RelationIsValid(rd))
		return rd;

	/*
	 * no reldesc in the cache, so have RelationBuildDesc() build one and add
	 * it.
	 */
	rd = RelationBuildDesc(relationId, NULL);
	if (RelationIsValid(rd))
		RelationIncrementReferenceCount(rd);
	return rd;
}

/* ----------------------------------------------------------------
 *				cache invalidation support routines
 * ----------------------------------------------------------------
 */

/*
 * RelationIncrementReferenceCount
 *		Increments relation reference count.
 *
 * Note: bootstrap mode has its own weird ideas about relation refcount
 * behavior; we ought to fix it someday, but for now, just disable
 * reference count ownership tracking in bootstrap mode.
 */
void
RelationIncrementReferenceCount(Relation rel)
{
	ResourceOwnerEnlargeRelationRefs(CurrentResourceOwner);
	rel->rd_refcnt += 1;
	if (!IsBootstrapProcessingMode())
		ResourceOwnerRememberRelationRef(CurrentResourceOwner, rel);
}

/*
 * RelationDecrementReferenceCount
 *		Decrements relation reference count.
 */
void
RelationDecrementReferenceCount(Relation rel)
{
	Assert(rel->rd_refcnt > 0);
	rel->rd_refcnt -= 1;
	if (!IsBootstrapProcessingMode())
		ResourceOwnerForgetRelationRef(CurrentResourceOwner, rel);
}

/*
 * RelationClose - close an open relation
 *
 *	Actually, we just decrement the refcount.
 *
 *	NOTE: if compiled with -DRELCACHE_FORCE_RELEASE then relcache entries
 *	will be freed as soon as their refcount goes to zero.  In combination
 *	with aset.c's CLOBBER_FREED_MEMORY option, this provides a good test
 *	to catch references to already-released relcache entries.  It slows
 *	things down quite a bit, however.
 */
void
RelationClose(Relation relation)
{
	/* Note: no locking manipulations needed */
	RelationDecrementReferenceCount(relation);

#ifdef RELCACHE_FORCE_RELEASE
	if (RelationHasReferenceCountZero(relation) &&
		relation->rd_createSubid == InvalidSubTransactionId)
		RelationClearRelation(relation, false);
#endif
}

/*
 * RelationReloadClassinfo - reload the pg_class row (only)
 *
 *	This function is used only for indexes.  We currently allow only the
 *	pg_class row of an existing index to change (to support changes of
 *	owner, tablespace, or relfilenode), not its pg_index row or other
 *	subsidiary index schema information.  Therefore it's sufficient to do
 *	this when we get an SI invalidation.  Furthermore, there are cases
 *	where it's necessary not to throw away the index information, especially
 *	for "nailed" indexes which we are unable to rebuild on-the-fly.
 *
 *	We can't necessarily reread the pg_class row right away; we might be
 *	in a failed transaction when we receive the SI notification.  If so,
 *	RelationClearRelation just marks the entry as invalid by setting
 *	rd_isvalid to false.  This routine is called to fix the entry when it
 *	is next needed.
 */
static void
RelationReloadClassinfo(Relation relation)
{
	bool		indexOK;
	HeapTuple	pg_class_tuple;
	Form_pg_class relp;

	/* Should be called only for invalidated indexes */
	Assert(relation->rd_rel->relkind == RELKIND_INDEX &&
		   !relation->rd_isvalid);
	/* Should be closed at smgr level */
	Assert(relation->rd_smgr == NULL);

	/*
	 * Read the pg_class row
	 *
	 * Don't try to use an indexscan of pg_class_oid_index to reload the info
	 * for pg_class_oid_index ...
	 */
	indexOK = (RelationGetRelid(relation) != ClassOidIndexId);
	pg_class_tuple = ScanPgRelation(RelationGetRelid(relation), indexOK);
	if (!HeapTupleIsValid(pg_class_tuple))
		elog(ERROR, "could not find pg_class tuple for index %u",
			 RelationGetRelid(relation));
	relp = (Form_pg_class) GETSTRUCT(pg_class_tuple);
	memcpy(relation->rd_rel, relp, CLASS_TUPLE_SIZE);
	heap_freetuple(pg_class_tuple);
	/* We must recalculate physical address in case it changed */
	RelationInitPhysicalAddr(relation);
	/* Make sure targblock is reset in case rel was truncated */
	relation->rd_targblock = InvalidBlockNumber;
	/* Okay, now it's valid again */
	relation->rd_isvalid = true;
}

/*
 * RelationClearRelation
 *
 *	 Physically blow away a relation cache entry, or reset it and rebuild
 *	 it from scratch (that is, from catalog entries).  The latter path is
 *	 usually used when we are notified of a change to an open relation
 *	 (one with refcount > 0).  However, this routine just does whichever
 *	 it's told to do; callers must determine which they want.
 */
static void
RelationClearRelation(Relation relation, bool rebuild)
{
	Oid			old_reltype = relation->rd_rel->reltype;
	MemoryContext oldcxt;

	/*
	 * Make sure smgr and lower levels close the relation's files, if they
	 * weren't closed already.  If the relation is not getting deleted, the
	 * next smgr access should reopen the files automatically.	This ensures
	 * that the low-level file access state is updated after, say, a vacuum
	 * truncation.
	 */
	RelationCloseSmgr(relation);

	/*
	 * Never, never ever blow away a nailed-in system relation, because we'd
	 * be unable to recover.  However, we must reset rd_targblock, in case we
	 * got called because of a relation cache flush that was triggered by
	 * VACUUM.
	 *
	 * If it's a nailed index, then we need to re-read the pg_class row to see
	 * if its relfilenode changed.	We can't necessarily do that here, because
	 * we might be in a failed transaction.  We assume it's okay to do it if
	 * there are open references to the relcache entry (cf notes for
	 * AtEOXact_RelationCache).  Otherwise just mark the entry as possibly
	 * invalid, and it'll be fixed when next opened.
	 */
	if (relation->rd_isnailed)
	{
		relation->rd_targblock = InvalidBlockNumber;
		if (relation->rd_rel->relkind == RELKIND_INDEX)
		{
			relation->rd_isvalid = false;		/* needs to be revalidated */
			if (relation->rd_refcnt > 1)
				RelationReloadClassinfo(relation);
		}
		return;
	}

	/*
	 * Even non-system indexes should not be blown away if they are open and
	 * have valid index support information.  This avoids problems with active
	 * use of the index support information.  As with nailed indexes, we
	 * re-read the pg_class row to handle possible physical relocation of
	 * the index.
	 */
	if (relation->rd_rel->relkind == RELKIND_INDEX &&
		relation->rd_refcnt > 0 &&
		relation->rd_indexcxt != NULL)
	{
		relation->rd_isvalid = false;			/* needs to be revalidated */
		RelationReloadClassinfo(relation);
		return;
	}

	/*
	 * Remove relation from hash tables
	 *
	 * Note: we might be reinserting it momentarily, but we must not have it
	 * visible in the hash tables until it's valid again, so don't try to
	 * optimize this away...
	 */
	oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
	RelationCacheDelete(relation);
	MemoryContextSwitchTo(oldcxt);

	/* Clear out catcache's entries for this relation */
	CatalogCacheFlushRelation(RelationGetRelid(relation));

	/*
	 * Free all the subsidiary data structures of the relcache entry. We
	 * cannot free rd_att if we are trying to rebuild the entry, however,
	 * because pointers to it may be cached in various places. The rule
	 * manager might also have pointers into the rewrite rules. So to begin
	 * with, we can only get rid of these fields:
	 */
	FreeTriggerDesc(relation->trigdesc);
	if (relation->rd_indextuple)
		pfree(relation->rd_indextuple);
	if (relation->rd_am)
		pfree(relation->rd_am);
	if (relation->rd_rel)
		pfree(relation->rd_rel);
	list_free(relation->rd_indexlist);
	if (relation->rd_indexcxt)
		MemoryContextDelete(relation->rd_indexcxt);

	/*
	 * If we're really done with the relcache entry, blow it away. But if
	 * someone is still using it, reconstruct the whole deal without moving
	 * the physical RelationData record (so that the someone's pointer is
	 * still valid).
	 */
	if (!rebuild)
	{
		/* ok to zap remaining substructure */
		flush_rowtype_cache(old_reltype);
		FreeTupleDesc(relation->rd_att);
		if (relation->rd_rulescxt)
			MemoryContextDelete(relation->rd_rulescxt);
		pfree(relation);
	}
	else
	{
		/*
		 * When rebuilding an open relcache entry, must preserve ref count and
		 * rd_createSubid state.  Also attempt to preserve the tupledesc and
		 * rewrite-rule substructures in place.
		 *
		 * Note that this process does not touch CurrentResourceOwner; which
		 * is good because whatever ref counts the entry may have do not
		 * necessarily belong to that resource owner.
		 */
		Oid			save_relid = RelationGetRelid(relation);
		int			old_refcnt = relation->rd_refcnt;
		SubTransactionId old_createSubid = relation->rd_createSubid;
		TupleDesc	old_att = relation->rd_att;
		RuleLock   *old_rules = relation->rd_rules;
		MemoryContext old_rulescxt = relation->rd_rulescxt;

		if (RelationBuildDesc(save_relid, relation) != relation)
		{
			/* Should only get here if relation was deleted */
			flush_rowtype_cache(old_reltype);
			FreeTupleDesc(old_att);
			if (old_rulescxt)
				MemoryContextDelete(old_rulescxt);
			pfree(relation);
			elog(ERROR, "relation %u deleted while still in use", save_relid);
		}
		relation->rd_refcnt = old_refcnt;
		relation->rd_createSubid = old_createSubid;
		if (equalTupleDescs(old_att, relation->rd_att))
		{
			/* needn't flush typcache here */
			FreeTupleDesc(relation->rd_att);
			relation->rd_att = old_att;
		}
		else
		{
			flush_rowtype_cache(old_reltype);
			FreeTupleDesc(old_att);
		}
		if (equalRuleLocks(old_rules, relation->rd_rules))
		{
			if (relation->rd_rulescxt)
				MemoryContextDelete(relation->rd_rulescxt);
			relation->rd_rules = old_rules;
			relation->rd_rulescxt = old_rulescxt;
		}
		else
		{
			if (old_rulescxt)
				MemoryContextDelete(old_rulescxt);
		}
	}
}

/*
 * RelationFlushRelation
 *
 *	 Rebuild the relation if it is open (refcount > 0), else blow it away.
 */
static void
RelationFlushRelation(Relation relation)
{
	bool		rebuild;

	if (relation->rd_createSubid != InvalidSubTransactionId)
	{
		/*
		 * New relcache entries are always rebuilt, not flushed; else we'd
		 * forget the "new" status of the relation, which is a useful
		 * optimization to have.
		 */
		rebuild = true;
	}
	else
	{
		/*
		 * Pre-existing rels can be dropped from the relcache if not open.
		 */
		rebuild = !RelationHasReferenceCountZero(relation);
	}

	RelationClearRelation(relation, rebuild);
}

/*
 * RelationForgetRelation - unconditionally remove a relcache entry
 *
 *		   External interface for destroying a relcache entry when we
 *		   drop the relation.
 */
void
RelationForgetRelation(Oid rid)
{
	Relation	relation;

	RelationIdCacheLookup(rid, relation);

	if (!PointerIsValid(relation))
		return;					/* not in cache, nothing to do */

	if (!RelationHasReferenceCountZero(relation))
		elog(ERROR, "relation %u is still open", rid);

	/* Unconditionally destroy the relcache entry */
	RelationClearRelation(relation, false);
}

/*
 *		RelationCacheInvalidateEntry
 *
 *		This routine is invoked for SI cache flush messages.
 *
 * Any relcache entry matching the relid must be flushed.  (Note: caller has
 * already determined that the relid belongs to our database or is a shared
 * relation.)
 *
 * We used to skip local relations, on the grounds that they could
 * not be targets of cross-backend SI update messages; but it seems
 * safer to process them, so that our *own* SI update messages will
 * have the same effects during CommandCounterIncrement for both
 * local and nonlocal relations.
 */
void
RelationCacheInvalidateEntry(Oid relationId)
{
	Relation	relation;

	RelationIdCacheLookup(relationId, relation);

	if (PointerIsValid(relation))
	{
		relcacheInvalsReceived++;
		RelationFlushRelation(relation);
	}
}

/*
 * RelationCacheInvalidate
 *	 Blow away cached relation descriptors that have zero reference counts,
 *	 and rebuild those with positive reference counts.	Also reset the smgr
 *	 relation cache.
 *
 *	 This is currently used only to recover from SI message buffer overflow,
 *	 so we do not touch new-in-transaction relations; they cannot be targets
 *	 of cross-backend SI updates (and our own updates now go through a
 *	 separate linked list that isn't limited by the SI message buffer size).
 *
 *	 We do this in two phases: the first pass deletes deletable items, and
 *	 the second one rebuilds the rebuildable items.  This is essential for
 *	 safety, because hash_seq_search only copes with concurrent deletion of
 *	 the element it is currently visiting.	If a second SI overflow were to
 *	 occur while we are walking the table, resulting in recursive entry to
 *	 this routine, we could crash because the inner invocation blows away
 *	 the entry next to be visited by the outer scan.  But this way is OK,
 *	 because (a) during the first pass we won't process any more SI messages,
 *	 so hash_seq_search will complete safely; (b) during the second pass we
 *	 only hold onto pointers to nondeletable entries.
 *
 *	 The two-phase approach also makes it easy to ensure that we process
 *	 nailed-in-cache indexes before other nondeletable items, and that we
 *	 process pg_class_oid_index first of all.  In scenarios where a nailed
 *	 index has been given a new relfilenode, we have to detect that update
 *	 before the nailed index is used in reloading any other relcache entry.
 */
void
RelationCacheInvalidate(void)
{
	HASH_SEQ_STATUS status;
	RelIdCacheEnt *idhentry;
	Relation	relation;
	List	   *rebuildFirstList = NIL;
	List	   *rebuildList = NIL;
	ListCell   *l;

	/* Phase 1 */
	hash_seq_init(&status, RelationIdCache);

	while ((idhentry = (RelIdCacheEnt *) hash_seq_search(&status)) != NULL)
	{
		relation = idhentry->reldesc;

		/* Must close all smgr references to avoid leaving dangling ptrs */
		RelationCloseSmgr(relation);

		/* Ignore new relations, since they are never SI targets */
		if (relation->rd_createSubid != InvalidSubTransactionId)
			continue;

		relcacheInvalsReceived++;

		if (RelationHasReferenceCountZero(relation))
		{
			/* Delete this entry immediately */
			Assert(!relation->rd_isnailed);
			RelationClearRelation(relation, false);
		}
		else
		{
			/*
			 * Add this entry to list of stuff to rebuild in second pass.
			 * pg_class_oid_index goes on the front of rebuildFirstList, other
			 * nailed indexes on the back, and everything else into
			 * rebuildList (in no particular order).
			 */
			if (relation->rd_isnailed &&
				relation->rd_rel->relkind == RELKIND_INDEX)
			{
				if (RelationGetRelid(relation) == ClassOidIndexId)