/*
* CatalogCacheComputeHashValue
*
* Compute the hash value associated with a given set of lookup keys
*/
static uint32
CatalogCacheComputeHashValue(CatCache *cache, int nkeys, ScanKey cur_skey)
{
uint32 hashValue = 0;
uint32 oneHash;
CACHE4_elog(DEBUG2, "CatalogCacheComputeHashValue %s %d %p",
cache->cc_relname,
nkeys,
cache);
switch (nkeys)
{
case 4:
oneHash =
DatumGetUInt32(DirectFunctionCall1(cache->cc_hashfunc[3],
cur_skey[3].sk_argument));
hashValue ^= oneHash << 24;
hashValue ^= oneHash >> 8;
/* FALLTHROUGH */
case 3:
oneHash =
DatumGetUInt32(DirectFunctionCall1(cache->cc_hashfunc[2],
cur_skey[2].sk_argument));
hashValue ^= oneHash << 16;
hashValue ^= oneHash >> 16;
/* FALLTHROUGH */
case 2:
oneHash =
DatumGetUInt32(DirectFunctionCall1(cache->cc_hashfunc[1],
cur_skey[1].sk_argument));
hashValue ^= oneHash << 8;
hashValue ^= oneHash >> 24;
/* FALLTHROUGH */
case 1:
oneHash =
DatumGetUInt32(DirectFunctionCall1(cache->cc_hashfunc[0],
cur_skey[0].sk_argument));
hashValue ^= oneHash;
break;
default:
elog(FATAL, "wrong number of hash keys: %d", nkeys);
break;
}
return hashValue;
}
static void
CatalogCacheInitializeCache(CatCache *cache)
{
Relation relation;
MemoryContext oldcxt;
TupleDesc tupdesc;
int i;
CatalogCacheInitializeCache_DEBUG1;
relation = heap_open(cache->cc_reloid, AccessShareLock);
/*
* switch to the cache context so our allocations do not vanish at the end
* of a transaction
*/
Assert(CacheMemoryContext != NULL);
oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
/*
* copy the relcache's tuple descriptor to permanent cache storage
*/
tupdesc = CreateTupleDescCopyConstr(RelationGetDescr(relation));
/*
* save the relation's name and relisshared flag, too (cc_relname is used
* only for debugging purposes)
*/
cache->cc_relname = pstrdup(RelationGetRelationName(relation));
cache->cc_relisshared = RelationGetForm(relation)->relisshared;
/*
* return to the caller's memory context and close the rel
*/
MemoryContextSwitchTo(oldcxt);
heap_close(relation, AccessShareLock);
CACHE3_elog(DEBUG2, "CatalogCacheInitializeCache: %s, %d keys",
cache->cc_relname, cache->cc_nkeys);
/*
* initialize cache's key information
*/
for (i = 0; i < cache->cc_nkeys; ++i)
{
Oid keytype;
RegProcedure eqfunc;
CatalogCacheInitializeCache_DEBUG2;
if (cache->cc_key[i] > 0)
keytype = tupdesc->attrs[cache->cc_key[i] - 1]->atttypid;
else
{
if (cache->cc_key[i] != ObjectIdAttributeNumber)
elog(FATAL, "only sys attr supported in caches is OID");
keytype = OIDOID;
}
GetCCHashEqFuncs(keytype,
&cache->cc_hashfunc[i],
&eqfunc);
cache->cc_isname[i] = (keytype == NAMEOID);
/*
* Do equality-function lookup (we assume this won't need a catalog
* lookup for any supported type)
*/
fmgr_info_cxt(eqfunc,
&cache->cc_skey[i].sk_func,
CacheMemoryContext);
/* Initialize sk_attno suitably for HeapKeyTest() and heap scans */
cache->cc_skey[i].sk_attno = cache->cc_key[i];
/* Fill in sk_strategy as well --- always standard equality */
cache->cc_skey[i].sk_strategy = BTEqualStrategyNumber;
cache->cc_skey[i].sk_subtype = InvalidOid;
/* Currently, there are no catcaches on collation-aware data types */
cache->cc_skey[i].sk_collation = InvalidOid;
CACHE4_elog(DEBUG2, "CatalogCacheInitializeCache %s %d %p",
cache->cc_relname,
i,
cache);
}
/*
* mark this cache fully initialized
*/
cache->cc_tupdesc = tupdesc;
}
/*
* SearchCatCache
*
* This call searches a system cache for a tuple, opening the relation
* if necessary (on the first access to a particular cache).
*
* The result is NULL if not found, or a pointer to a HeapTuple in
* the cache. The caller must not modify the tuple, and must call
* ReleaseCatCache() when done with it.
*
* The search key values should be expressed as Datums of the key columns'
* datatype(s). (Pass zeroes for any unused parameters.) As a special
* exception, the passed-in key for a NAME column can be just a C string;
* the caller need not go to the trouble of converting it to a fully
* null-padded NAME.
*/
HeapTuple
SearchCatCache(CatCache *cache,
Datum v1,
Datum v2,
Datum v3,
Datum v4)
{
ScanKeyData cur_skey[CATCACHE_MAXKEYS];
uint32 hashValue;
Index hashIndex;
Dlelem *elt;
CatCTup *ct;
Relation relation;
SysScanDesc scandesc;
HeapTuple ntp;
/*
* one-time startup overhead for each cache
*/
if (cache->cc_tupdesc == NULL)
CatalogCacheInitializeCache(cache);
#ifdef CATCACHE_STATS
cache->cc_searches++;
#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;
/*
* find the hash bucket in which to look for the tuple
*/
hashValue = CatalogCacheComputeHashValue(cache, cache->cc_nkeys, cur_skey);
hashIndex = HASH_INDEX(hashValue, cache->cc_nbuckets);
/*
* scan the hash bucket until we find a match or exhaust our tuples
*/
for (elt = DLGetHead(&cache->cc_bucket[hashIndex]);
elt;
elt = DLGetSucc(elt))
{
bool res;
ct = (CatCTup *) DLE_VAL(elt);
if (ct->dead)
continue; /* ignore dead entries */
if (ct->hash_value != hashValue)
continue; /* quickly skip entry if wrong hash val */
/*
* see if the cached tuple matches our key.
*/
HeapKeyTest(&ct->tuple,
cache->cc_tupdesc,
cache->cc_nkeys,
cur_skey,
res);
if (!res)
continue;
/*
* We found a match in the cache. Move it to the front of the list
* for its hashbucket, in order to speed subsequent searches. (The
* most frequently accessed elements in any hashbucket will tend to be
* near the front of the hashbucket's list.)
*/
DLMoveToFront(&ct->cache_elem);
/*
* If it's a positive entry, bump its refcount and return it. If it's
* negative, we can report failure to the caller.
*/
if (!ct->negative)
{
ResourceOwnerEnlargeCatCacheRefs(CurrentResourceOwner);
ct->refcount++;
ResourceOwnerRememberCatCacheRef(CurrentResourceOwner, &ct->tuple);
CACHE3_elog(DEBUG2, "SearchCatCache(%s): found in bucket %d",
cache->cc_relname, hashIndex);
#ifdef CATCACHE_STATS
cache->cc_hits++;
#endif
return &ct->tuple;
}
else
{
CACHE3_elog(DEBUG2, "SearchCatCache(%s): found neg entry in bucket %d",
cache->cc_relname, hashIndex);
#ifdef CATCACHE_STATS
cache->cc_neg_hits++;
#endif
return NULL;
}
}
/*
* Tuple was not found in cache, so we have to try to retrieve it directly
* from the relation. If found, we will add it to the cache; if not
* found, we will add a negative cache entry instead.
*
* 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_indexoid,
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);
/* immediately set the refcount to 1 */
ResourceOwnerEnlargeCatCacheRefs(CurrentResourceOwner);
ct->refcount++;
ResourceOwnerRememberCatCacheRef(CurrentResourceOwner, &ct->tuple);
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.
*
* In bootstrap mode, we don't build negative entries, because the cache
* invalidation mechanism isn't alive and can't clear them if the tuple
* gets created later. (Bootstrap doesn't do UPDATEs, so it doesn't need
* cache inval for that.)
*/
if (ct == NULL)
{
if (IsBootstrapProcessingMode())
return 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 negative entry to the caller, so leave its
* refcount zero.
*/
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;
}
static void
CatalogCacheInitializeCache(CatCache *cache)
{
Relation relation;
MemoryContext oldcxt;
TupleDesc tupdesc;
int i;
CatalogCacheInitializeCache_DEBUG2;
/*
* Open the relation without locking --- we only need the tupdesc,
* which we assume will never change ...
*/
relation = heap_openr(cache->cc_relname, NoLock);
Assert(RelationIsValid(relation));
/*
* switch to the cache context so our allocations do not vanish at the
* end of a transaction
*/
Assert(CacheMemoryContext != NULL);
oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
/*
* copy the relcache's tuple descriptor to permanent cache storage
*/
tupdesc = CreateTupleDescCopyConstr(RelationGetDescr(relation));
/*
* get the relation's OID and relisshared flag, too
*/
cache->cc_reloid = RelationGetRelid(relation);
cache->cc_relisshared = RelationGetForm(relation)->relisshared;
/*
* return to the caller's memory context and close the rel
*/
MemoryContextSwitchTo(oldcxt);
heap_close(relation, NoLock);
CACHE3_elog(DEBUG2, "CatalogCacheInitializeCache: %s, %d keys",
cache->cc_relname, cache->cc_nkeys);
/*
* initialize cache's key information
*/
for (i = 0; i < cache->cc_nkeys; ++i)
{
Oid keytype;
CatalogCacheInitializeCache_DEBUG2;
if (cache->cc_key[i] > 0)
keytype = tupdesc->attrs[cache->cc_key[i] - 1]->atttypid;
else
{
if (cache->cc_key[i] != ObjectIdAttributeNumber)
elog(FATAL, "only sys attr supported in caches is OID");
keytype = OIDOID;
}
GetCCHashEqFuncs(keytype,
&cache->cc_hashfunc[i],
&cache->cc_skey[i].sk_procedure);
cache->cc_isname[i] = (keytype == NAMEOID);
/*
* Do equality-function lookup (we assume this won't need a
* catalog lookup for any supported type)
*/
fmgr_info_cxt(cache->cc_skey[i].sk_procedure,
&cache->cc_skey[i].sk_func,
CacheMemoryContext);
/* Initialize sk_attno suitably for HeapKeyTest() and heap scans */
cache->cc_skey[i].sk_attno = cache->cc_key[i];
CACHE4_elog(DEBUG2, "CatalogCacheInit %s %d %p",
cache->cc_relname,
i,
cache);
}
/*
* mark this cache fully initialized
*/
cache->cc_tupdesc = tupdesc;
}