catcache.c

来自「PostgreSQL7.4.6 for Linux」· C语言 代码 · 共 1,777 行 · 第 1/3 页

	 *
	 * NOTE: it is possible for recursive cache lookups to occur while
	 * reading the relation --- for example, due to shared-cache-inval
	 * messages being processed during heap_open().  This is OK.  It's
	 * even possible for one of those lookups to find and enter the very
	 * same tuple we are trying to fetch here.	If that happens, we will
	 * enter a second copy of the tuple into the cache.  The first copy
	 * will never be referenced again, and will eventually age out of the
	 * cache, so there's no functional problem.  This case is rare enough
	 * that it's not worth expending extra cycles to detect.
	 */
	relation = heap_open(cache->cc_reloid, AccessShareLock);

	scandesc = systable_beginscan(relation,
								  cache->cc_indname,
								  IndexScanOK(cache, cur_skey),
								  SnapshotNow,
								  cache->cc_nkeys,
								  cur_skey);

	ct = NULL;

	while (HeapTupleIsValid(ntp = systable_getnext(scandesc)))
	{
		ct = CatalogCacheCreateEntry(cache, ntp,
									 hashValue, hashIndex,
									 false);
		break;					/* assume only one match */
	}

	systable_endscan(scandesc);

	heap_close(relation, AccessShareLock);

	/*
	 * If tuple was not found, we need to build a negative cache entry
	 * containing a fake tuple.  The fake tuple has the correct key
	 * columns, but nulls everywhere else.
	 */
	if (ct == NULL)
	{
		ntp = build_dummy_tuple(cache, cache->cc_nkeys, cur_skey);
		ct = CatalogCacheCreateEntry(cache, ntp,
									 hashValue, hashIndex,
									 true);
		heap_freetuple(ntp);

		CACHE4_elog(DEBUG2, "SearchCatCache(%s): Contains %d/%d tuples",
					cache->cc_relname, cache->cc_ntup, CacheHdr->ch_ntup);
		CACHE3_elog(DEBUG2, "SearchCatCache(%s): put neg entry in bucket %d",
					cache->cc_relname, hashIndex);

		/*
		 * We are not returning the new entry to the caller, so reset its
		 * refcount.
		 */
		ct->refcount = 0;		/* negative entries never have refs */

		return NULL;
	}

	CACHE4_elog(DEBUG2, "SearchCatCache(%s): Contains %d/%d tuples",
				cache->cc_relname, cache->cc_ntup, CacheHdr->ch_ntup);
	CACHE3_elog(DEBUG2, "SearchCatCache(%s): put in bucket %d",
				cache->cc_relname, hashIndex);

#ifdef CATCACHE_STATS
	cache->cc_newloads++;
#endif

	return &ct->tuple;
}

/*
 *	ReleaseCatCache
 *
 *	Decrement the reference count of a catcache entry (releasing the
 *	hold grabbed by a successful SearchCatCache).
 *
 *	NOTE: if compiled with -DCATCACHE_FORCE_RELEASE then catcache 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 catcache entries.
 */
void
ReleaseCatCache(HeapTuple tuple)
{
	CatCTup    *ct = (CatCTup *) (((char *) tuple) -
								  offsetof(CatCTup, tuple));

	/* Safety checks to ensure we were handed a cache entry */
	Assert(ct->ct_magic == CT_MAGIC);
	Assert(ct->refcount > 0);

	ct->refcount--;

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


/*
 *	SearchCatCacheList
 *
 *		Generate a list of all tuples matching a partial key (that is,
 *		a key specifying just the first K of the cache's N key columns).
 *
 *		The caller must not modify the list object or the pointed-to tuples,
 *		and must call ReleaseCatCacheList() when done with the list.
 */
CatCList *
SearchCatCacheList(CatCache *cache,
				   int nkeys,
				   Datum v1,
				   Datum v2,
				   Datum v3,
				   Datum v4)
{
	ScanKeyData cur_skey[4];
	uint32		lHashValue;
	Dlelem	   *elt;
	CatCList   *cl;
	CatCTup    *ct;
	List	   *ctlist;
	int			nmembers;
	Relation	relation;
	SysScanDesc scandesc;
	bool		ordered;
	HeapTuple	ntp;
	MemoryContext oldcxt;
	int			i;

	/*
	 * one-time startup overhead for each cache
	 */
	if (cache->cc_tupdesc == NULL)
		CatalogCacheInitializeCache(cache);

	Assert(nkeys > 0 && nkeys < cache->cc_nkeys);

#ifdef CATCACHE_STATS
	cache->cc_lsearches++;
#endif

	/*
	 * initialize the search key information
	 */
	memcpy(cur_skey, cache->cc_skey, sizeof(cur_skey));
	cur_skey[0].sk_argument = v1;
	cur_skey[1].sk_argument = v2;
	cur_skey[2].sk_argument = v3;
	cur_skey[3].sk_argument = v4;

	/*
	 * compute a hash value of the given keys for faster search.  We don't
	 * presently divide the CatCList items into buckets, but this still
	 * lets us skip non-matching items quickly most of the time.
	 */
	lHashValue = CatalogCacheComputeHashValue(cache, nkeys, cur_skey);

	/*
	 * scan the items until we find a match or exhaust our list
	 */
	for (elt = DLGetHead(&cache->cc_lists);
		 elt;
		 elt = DLGetSucc(elt))
	{
		bool		res;

		cl = (CatCList *) DLE_VAL(elt);

		if (cl->dead)
			continue;			/* ignore dead entries */

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

		/*
		 * see if the cached list matches our key.
		 */
		if (cl->nkeys != nkeys)
			continue;
		HeapKeyTest(&cl->tuple,
					cache->cc_tupdesc,
					nkeys,
					cur_skey,
					res);
		if (!res)
			continue;

		/*
		 * we found a matching list: move each of its members to the front
		 * of the global LRU list.	Also move the list itself to the front
		 * of the cache's list-of-lists, to speed subsequent searches. (We
		 * do not move the members to the fronts of their hashbucket
		 * lists, however, since there's no point in that unless they are
		 * searched for individually.)	Also bump the members' refcounts.
		 */
		for (i = 0; i < cl->n_members; i++)
		{
			cl->members[i]->refcount++;
			DLMoveToFront(&cl->members[i]->lrulist_elem);
		}
		DLMoveToFront(&cl->cache_elem);

		/* Bump the list's refcount and return it */
		cl->refcount++;

		CACHE2_elog(DEBUG2, "SearchCatCacheList(%s): found list",
					cache->cc_relname);

#ifdef CATCACHE_STATS
		cache->cc_lhits++;
#endif

		return cl;
	}

	/*
	 * List was not found in cache, so we have to build it by reading the
	 * relation.  For each matching tuple found in the relation, use an
	 * existing cache entry if possible, else build a new one.
	 */
	relation = heap_open(cache->cc_reloid, AccessShareLock);

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

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

	ctlist = NIL;
	nmembers = 0;

	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 bump its refcount and move to front */
			ct->refcount++;

			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);
		}

		ctlist = lcons(ct, ctlist);
		nmembers++;
	}

	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);
	cl = (CatCList *) palloc(sizeof(CatCList) + nmembers * sizeof(CatCTup *));
	heap_copytuple_with_tuple(ntp, &cl->tuple);
	MemoryContextSwitchTo(oldcxt);
	heap_freetuple(ntp);

	cl->cl_magic = CL_MAGIC;
	cl->my_cache = cache;
	DLInitElem(&cl->cache_elem, (void *) cl);
	cl->refcount = 1;			/* count this first reference */
	cl->dead = false;
	cl->ordered = ordered;
	cl->nkeys = nkeys;
	cl->hash_value = lHashValue;
	cl->n_members = nmembers;
	/* The list is backwards because we built it with lcons */
	for (i = nmembers; --i >= 0;)
	{
		cl->members[i] = ct = (CatCTup *) lfirst(ctlist);
		Assert(ct->c_list == NULL);
		ct->c_list = cl;
		/* mark list dead if any members already dead */
		if (ct->dead)
			cl->dead = true;
		ctlist = lnext(ctlist);
	}

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

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

	return cl;
}

/*
 *	ReleaseCatCacheList
 *
 *	Decrement the reference counts of a catcache list.
 */
void
ReleaseCatCacheList(CatCList *list)
{
	int			i;

	/* Safety checks to ensure we were handed a cache entry */
	Assert(list->cl_magic == CL_MAGIC);
	Assert(list->refcount > 0);

	for (i = list->n_members; --i >= 0;)
	{
		CatCTup    *ct = list->members[i];

		Assert(ct->refcount > 0);

		ct->refcount--;

		if (ct->dead)
			list->dead = true;
		/* can't remove tuple before list is removed */
	}

	list->refcount--;

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


/*
 * CatalogCacheCreateEntry
 *		Create a new CatCTup entry, copying the given HeapTuple and other
 *		supplied data into it.	The new entry is given refcount 1.
 */
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 = 1;			/* count this first reference */
	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.  NB: the newly-built entry cannot
	 * get thrown away here, because it has positive refcount.
	 */
	if (CacheHdr->ch_ntup > CacheHdr->ch_maxtup)
	{
		Dlelem	   *elt,
				   *prevelt;

		for (elt = DLGetTail(&CacheHdr->ch_lrulist); elt; elt = prevelt)
		{
			CatCTup    *oldct = (CatCTup *) DLE_VAL(elt);

			prevelt = DLGetPred(elt);

			if (oldct->refcount == 0)
			{
				CACHE2_elog(DEBUG2, "CatCacheCreateEntry(%s): Overflow, LRU removal",
							cache->cc_relname);
#ifdef CATCACHE_STATS
				oldct->my_cache->cc_discards++;
#endif
				CatCacheRemoveCTup(oldct->my_cache, oldct);
				if (CacheHdr->ch_ntup <= CacheHdr->ch_maxtup)
					break;
			}
		}
	}

	return ct;
}

/*
 * 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);
	}
}