catcache.c

来自「PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统」· C语言 代码 · 共 1,927 行 · 第 1/4 页

	 * We have to bump the member refcounts temporarily to ensure they won't
	 * get dropped from the cache while loading other members. We use a PG_TRY
	 * block to ensure we can undo those refcounts if we get an error before
	 * we finish constructing the CatCList.
	 */
	ResourceOwnerEnlargeCatCacheListRefs(CurrentResourceOwner);

	ctlist = NIL;

	PG_TRY();
	{
		Relation	relation;
		SysScanDesc scandesc;

		relation = heap_open(cache->cc_reloid, AccessShareLock);

		scandesc = systable_beginscan(relation,
									  cache->cc_indexoid,
									  true,
									  SnapshotNow,
									  nkeys,
									  cur_skey);

		/* The list will be ordered iff we are doing an index scan */
		ordered = (scandesc->irel != NULL);

		while (HeapTupleIsValid(ntp = systable_getnext(scandesc)))
		{
			uint32		hashValue;
			Index		hashIndex;

			/*
			 * See if there's an entry for this tuple already.
			 */
			ct = NULL;
			hashValue = CatalogCacheComputeTupleHashValue(cache, ntp);
			hashIndex = HASH_INDEX(hashValue, cache->cc_nbuckets);

			for (elt = DLGetHead(&cache->cc_bucket[hashIndex]);
				 elt;
				 elt = DLGetSucc(elt))
			{
				ct = (CatCTup *) DLE_VAL(elt);

				if (ct->dead || ct->negative)
					continue;	/* ignore dead and negative entries */

				if (ct->hash_value != hashValue)
					continue;	/* quickly skip entry if wrong hash val */

				if (!ItemPointerEquals(&(ct->tuple.t_self), &(ntp->t_self)))
					continue;	/* not same tuple */

				/*
				 * Found a match, but can't use it if it belongs to another
				 * list already
				 */
				if (ct->c_list)
					continue;

				/* Found a match, so move it to front */
				DLMoveToFront(&ct->lrulist_elem);

				break;
			}

			if (elt == NULL)
			{
				/* We didn't find a usable entry, so make a new one */
				ct = CatalogCacheCreateEntry(cache, ntp,
											 hashValue, hashIndex,
											 false);
			}

			/* Careful here: add entry to ctlist, then bump its refcount */
			/* This way leaves state correct if lappend runs out of memory */
			ctlist = lappend(ctlist, ct);
			ct->refcount++;
		}

		systable_endscan(scandesc);

		heap_close(relation, AccessShareLock);

		/*
		 * Now we can build the CatCList entry.  First we need a dummy tuple
		 * containing the key values...
		 */
		ntp = build_dummy_tuple(cache, nkeys, cur_skey);
		oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
		nmembers = list_length(ctlist);
		cl = (CatCList *)
			palloc(sizeof(CatCList) + nmembers * sizeof(CatCTup *));
		heap_copytuple_with_tuple(ntp, &cl->tuple);
		MemoryContextSwitchTo(oldcxt);
		heap_freetuple(ntp);

		/*
		 * We are now past the last thing that could trigger an elog before we
		 * have finished building the CatCList and remembering it in the
		 * resource owner.	So it's OK to fall out of the PG_TRY, and indeed
		 * we'd better do so before we start marking the members as belonging
		 * to the list.
		 */

	}
	PG_CATCH();
	{
		foreach(ctlist_item, ctlist)
		{
			ct = (CatCTup *) lfirst(ctlist_item);
			Assert(ct->c_list == NULL);
			Assert(ct->refcount > 0);
			ct->refcount--;
			if (
#ifndef CATCACHE_FORCE_RELEASE
				ct->dead &&
#endif
				ct->refcount == 0 &&
				(ct->c_list == NULL || ct->c_list->refcount == 0))
				CatCacheRemoveCTup(cache, ct);
		}

		PG_RE_THROW();
	}
	PG_END_TRY();

	cl->cl_magic = CL_MAGIC;
	cl->my_cache = cache;
	DLInitElem(&cl->cache_elem, cl);
	cl->refcount = 0;			/* for the moment */
	cl->dead = false;
	cl->ordered = ordered;
	cl->touched = false;		/* we already moved members to front */
	cl->nkeys = nkeys;
	cl->hash_value = lHashValue;
	cl->n_members = nmembers;

	i = 0;
	foreach(ctlist_item, ctlist)
	{
		cl->members[i++] = ct = (CatCTup *) lfirst(ctlist_item);
		Assert(ct->c_list == NULL);
		ct->c_list = cl;
		/* release the temporary refcount on the member */
		Assert(ct->refcount > 0);
		ct->refcount--;
		/* mark list dead if any members already dead */
		if (ct->dead)
			cl->dead = true;
	}
	Assert(i == nmembers);

	DLAddHead(&cache->cc_lists, &cl->cache_elem);

	/* Finally, bump the list's refcount and return it */
	cl->refcount++;
	ResourceOwnerRememberCatCacheListRef(CurrentResourceOwner, cl);

	CACHE3_elog(DEBUG2, "SearchCatCacheList(%s): made list of %d members",
				cache->cc_relname, nmembers);

	return cl;
}

/*
 *	ReleaseCatCacheList
 *
 *	Decrement the reference count of a catcache list.
 */
void
ReleaseCatCacheList(CatCList *list)
{
	/* Safety checks to ensure we were handed a cache entry */
	Assert(list->cl_magic == CL_MAGIC);
	Assert(list->refcount > 0);
	list->refcount--;
	ResourceOwnerForgetCatCacheListRef(CurrentResourceOwner, list);

	if (
#ifndef CATCACHE_FORCE_RELEASE
		list->dead &&
#endif
		list->refcount == 0)
		CatCacheRemoveCList(list->my_cache, list);
}


/*
 * CatalogCacheCreateEntry
 *		Create a new CatCTup entry, copying the given HeapTuple and other
 *		supplied data into it.	The new entry initially has refcount 0.
 */
static CatCTup *
CatalogCacheCreateEntry(CatCache *cache, HeapTuple ntp,
						uint32 hashValue, Index hashIndex, bool negative)
{
	CatCTup    *ct;
	MemoryContext oldcxt;

	/*
	 * Allocate CatCTup header in cache memory, and copy the tuple there too.
	 */
	oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
	ct = (CatCTup *) palloc(sizeof(CatCTup));
	heap_copytuple_with_tuple(ntp, &ct->tuple);
	MemoryContextSwitchTo(oldcxt);

	/*
	 * Finish initializing the CatCTup header, and add it to the cache's
	 * linked lists and counts.
	 */
	ct->ct_magic = CT_MAGIC;
	ct->my_cache = cache;
	DLInitElem(&ct->lrulist_elem, (void *) ct);
	DLInitElem(&ct->cache_elem, (void *) ct);
	ct->c_list = NULL;
	ct->refcount = 0;			/* for the moment */
	ct->dead = false;
	ct->negative = negative;
	ct->hash_value = hashValue;

	DLAddHead(&CacheHdr->ch_lrulist, &ct->lrulist_elem);
	DLAddHead(&cache->cc_bucket[hashIndex], &ct->cache_elem);

	cache->cc_ntup++;
	CacheHdr->ch_ntup++;

	/*
	 * If we've exceeded the desired size of the caches, try to throw away the
	 * least recently used entry(s).  NB: be careful not to throw away the
	 * newly-built entry...
	 */
	if (CacheHdr->ch_ntup > CacheHdr->ch_maxtup)
		CatalogCacheCleanup(ct);

	return ct;
}

/*
 * CatalogCacheCleanup
 *		Try to reduce the size of the catcaches when they get too big
 *
 * savect can be NULL, or a specific CatCTup not to remove even if it
 * has zero refcount.
 */
static void
CatalogCacheCleanup(CatCTup *savect)
{
	int			tup_target;
	CatCache   *ccp;
	Dlelem	   *elt,
			   *prevelt;

	/*
	 * Each time we have to do this, try to cut the cache size down to about
	 * 90% of the maximum.
	 */
	tup_target = (CacheHdr->ch_maxtup * 9) / 10;

	/*
	 * Our strategy for managing CatCLists is that, each time we have to throw
	 * away some cache entries, we first move-to-front all the members of
	 * CatCLists that have been touched since the last cleanup sweep. Then we
	 * do strict LRU elimination by individual tuples, zapping a list if any
	 * of its members gets zapped.	Before PostgreSQL 8.1, we moved members to
	 * front each time their owning list was touched, which was arguably more
	 * fair in balancing list members against standalone tuples --- but the
	 * overhead for large lists was horrendous.  This scheme is more heavily
	 * biased towards preserving lists, but that is not necessarily bad
	 * either.
	 */
	for (ccp = CacheHdr->ch_caches; ccp; ccp = ccp->cc_next)
	{
		for (elt = DLGetHead(&ccp->cc_lists); elt; elt = DLGetSucc(elt))
		{
			CatCList   *cl = (CatCList *) DLE_VAL(elt);

			Assert(cl->cl_magic == CL_MAGIC);
			if (cl->touched && !cl->dead)
			{
				int			i;

				for (i = 0; i < cl->n_members; i++)
					DLMoveToFront(&cl->members[i]->lrulist_elem);
			}
			cl->touched = false;
		}
	}

	/* Now get rid of unreferenced tuples in reverse global LRU order */
	for (elt = DLGetTail(&CacheHdr->ch_lrulist); elt; elt = prevelt)
	{
		CatCTup    *ct = (CatCTup *) DLE_VAL(elt);

		prevelt = DLGetPred(elt);

		if (ct->refcount == 0 &&
			(ct->c_list == NULL || ct->c_list->refcount == 0) &&
			ct != savect)
		{
#ifdef CATCACHE_STATS
			ct->my_cache->cc_discards++;
#endif
			CatCacheRemoveCTup(ct->my_cache, ct);

			/* Quit when we've removed enough tuples */
			if (CacheHdr->ch_ntup <= tup_target)
				break;
		}
	}
}

/*
 * build_dummy_tuple
 *		Generate a palloc'd HeapTuple that contains the specified key
 *		columns, and NULLs for other columns.
 *
 * This is used to store the keys for negative cache entries and CatCList
 * entries, which don't have real tuples associated with them.
 */
static HeapTuple
build_dummy_tuple(CatCache *cache, int nkeys, ScanKey skeys)
{
	HeapTuple	ntp;
	TupleDesc	tupDesc = cache->cc_tupdesc;
	Datum	   *values;
	char	   *nulls;
	Oid			tupOid = InvalidOid;
	NameData	tempNames[4];
	int			i;

	values = (Datum *) palloc(tupDesc->natts * sizeof(Datum));
	nulls = (char *) palloc(tupDesc->natts * sizeof(char));

	memset(values, 0, tupDesc->natts * sizeof(Datum));
	memset(nulls, 'n', tupDesc->natts * sizeof(char));

	for (i = 0; i < nkeys; i++)
	{
		int			attindex = cache->cc_key[i];
		Datum		keyval = skeys[i].sk_argument;

		if (attindex > 0)
		{
			/*
			 * Here we must be careful in case the caller passed a C string
			 * where a NAME is wanted: convert the given argument to a
			 * correctly padded NAME.  Otherwise the memcpy() done in
			 * heap_formtuple could fall off the end of memory.
			 */
			if (cache->cc_isname[i])
			{
				Name		newval = &tempNames[i];

				namestrcpy(newval, DatumGetCString(keyval));
				keyval = NameGetDatum(newval);
			}
			values[attindex - 1] = keyval;
			nulls[attindex - 1] = ' ';
		}
		else
		{
			Assert(attindex == ObjectIdAttributeNumber);
			tupOid = DatumGetObjectId(keyval);
		}
	}

	ntp = heap_formtuple(tupDesc, values, nulls);
	if (tupOid != InvalidOid)
		HeapTupleSetOid(ntp, tupOid);

	pfree(values);
	pfree(nulls);

	return ntp;
}


/*
 *	PrepareToInvalidateCacheTuple()
 *
 *	This is part of a rather subtle chain of events, so pay attention:
 *
 *	When a tuple is inserted or deleted, it cannot be flushed from the
 *	catcaches immediately, for reasons explained at the top of cache/inval.c.
 *	Instead we have to add entry(s) for the tuple to a list of pending tuple
 *	invalidations that will be done at the end of the command or transaction.
 *
 *	The lists of tuples that need to be flushed are kept by inval.c.  This
 *	routine is a helper routine for inval.c.  Given a tuple belonging to
 *	the specified relation, find all catcaches it could be in, compute the
 *	correct hash value for each such catcache, and call the specified function
 *	to record the cache id, hash value, and tuple ItemPointer in inval.c's
 *	lists.	CatalogCacheIdInvalidate will be called later, if appropriate,
 *	using the recorded information.
 *
 *	Note that it is irrelevant whether the given tuple is actually loaded
 *	into the catcache at the moment.  Even if it's not there now, it might
 *	be by the end of the command, or there might be a matching negative entry
 *	to flush --- or other backends' caches might have such entries --- so
 *	we have to make list entries to flush it later.
 *
 *	Also note that it's not an error if there are no catcaches for the
 *	specified relation.  inval.c doesn't know exactly which rels have
 *	catcaches --- it will call this routine for any tuple that's in a
 *	system relation.
 */
void
PrepareToInvalidateCacheTuple(Relation relation,
							  HeapTuple tuple,
							void (*function) (int, uint32, ItemPointer, Oid))
{
	CatCache   *ccp;
	Oid			reloid;

	CACHE1_elog(DEBUG2, "PrepareToInvalidateCacheTuple: called");

	/*
	 * sanity checks
	 */
	Assert(RelationIsValid(relation));
	Assert(HeapTupleIsValid(tuple));
	Assert(PointerIsValid(function));
	Assert(CacheHdr != NULL);

	reloid = RelationGetRelid(relation);

	/* ----------------
	 *	for each cache
	 *	   if the cache contains tuples from the specified relation
	 *		   compute the tuple's hash value in this cache,
	 *		   and call the passed function to register the information.
	 * ----------------
	 */

	for (ccp = CacheHdr->ch_caches; ccp; ccp = ccp->cc_next)
	{
		/* Just in case cache hasn't finished initialization yet... */
		if (ccp->cc_tupdesc == NULL)
			CatalogCacheInitializeCache(ccp);

		if (ccp->cc_reloid != reloid)
			continue;

		(*function) (ccp->id,
					 CatalogCacheComputeTupleHashValue(ccp, tuple),
					 &tuple->t_self,
					 ccp->cc_relisshared ? (Oid) 0 : MyDatabaseId);
	}
}


/*
 * Subroutines for warning about reference leaks.  These are exported so
 * that resowner.c can call them.
 */
void
PrintCatCacheLeakWarning(HeapTuple tuple)
{
	CatCTup    *ct = (CatCTup *) (((char *) tuple) -
								  offsetof(CatCTup, tuple));

	/* Safety check to ensure we were handed a cache entry */
	Assert(ct->ct_magic == CT_MAGIC);

	elog(WARNING, "cache reference leak: cache %s (%d), tuple %u/%u has count %d",
		 ct->my_cache->cc_relname, ct->my_cache->id,
		 ItemPointerGetBlockNumber(&(tuple->t_self)),
		 ItemPointerGetOffsetNumber(&(tuple->t_self)),
		 ct->refcount);
}

void
PrintCatCacheListLeakWarning(CatCList *list)
{
	elog(WARNING, "cache reference leak: cache %s (%d), list %p has count %d",
		 list->my_cache->cc_relname, list->my_cache->id,
		 list, list->refcount);
}