catcache.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * catcache.c
 *    System catalog cache for tuples matching a key.
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/cache/catcache.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/relscan.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "access/tuptoaster.h"
#include "access/valid.h"
#include "access/xact.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#ifdef CATCACHE_STATS
#include "storage/ipc.h"        /* for on_proc_exit */
#endif
#include "storage/lmgr.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/fmgroids.h"
#include "utils/hashutils.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/resowner_private.h"
#include "utils/syscache.h"


 /* #define CACHEDEBUG */   /* turns DEBUG elogs on */

/*
 * Given a hash value and the size of the hash table, find the bucket
 * in which the hash value belongs. Since the hash table must contain
 * a power-of-2 number of elements, this is a simple bitmask.
 */
#define HASH_INDEX(h, sz) ((Index) ((h) & ((sz) - 1)))


/*
 *      variables, macros and other stuff
 */

#ifdef CACHEDEBUG
#define CACHE_elog(...)             elog(__VA_ARGS__)
#else
#define CACHE_elog(...)
#endif

/* Cache management header --- pointer is NULL until created */
static CatCacheHeader *CacheHdr = NULL;

static inline HeapTuple SearchCatCacheInternal(CatCache *cache,
                                               int nkeys,
                                               Datum v1, Datum v2,
                                               Datum v3, Datum v4);

static pg_noinline HeapTuple SearchCatCacheMiss(CatCache *cache,
                                                int nkeys,
                                                uint32 hashValue,
                                                Index hashIndex,
                                                Datum v1, Datum v2,
                                                Datum v3, Datum v4);

static uint32 CatalogCacheComputeHashValue(CatCache *cache, int nkeys,
                                           Datum v1, Datum v2, Datum v3, Datum v4);
static uint32 CatalogCacheComputeTupleHashValue(CatCache *cache, int nkeys,
                                                HeapTuple tuple);
static inline bool CatalogCacheCompareTuple(const CatCache *cache, int nkeys,
                                            const Datum *cachekeys,
                                            const Datum *searchkeys);

#ifdef CATCACHE_STATS
static void CatCachePrintStats(int code, Datum arg);
#endif
static void CatCacheRemoveCTup(CatCache *cache, CatCTup *ct);
static void CatCacheRemoveCList(CatCache *cache, CatCList *cl);
static void CatalogCacheInitializeCache(CatCache *cache);
static CatCTup *CatalogCacheCreateEntry(CatCache *cache, HeapTuple ntp,
                                        Datum *arguments,
                                        uint32 hashValue, Index hashIndex,
                                        bool negative);

static void CatCacheFreeKeys(TupleDesc tupdesc, int nkeys, int *attnos,
                             Datum *keys);
static void CatCacheCopyKeys(TupleDesc tupdesc, int nkeys, int *attnos,
                             Datum *srckeys, Datum *dstkeys);


/*
 *                  internal support functions
 */

/*
 * Hash and equality functions for system types that are used as cache key
 * fields.  In some cases, we just call the regular SQL-callable functions for
 * the appropriate data type, but that tends to be a little slow, and the
 * speed of these functions is performance-critical.  Therefore, for data
 * types that frequently occur as catcache keys, we hard-code the logic here.
 * Avoiding the overhead of DirectFunctionCallN(...) is a substantial win, and
 * in certain cases (like int4) we can adopt a faster hash algorithm as well.
 */

static bool
chareqfast(Datum a, Datum b)
{
    return DatumGetChar(a) == DatumGetChar(b);
}

static uint32
charhashfast(Datum datum)
{
    return murmurhash32((int32) DatumGetChar(datum));
}

static bool
nameeqfast(Datum a, Datum b)
{
    char       *ca = NameStr(*DatumGetName(a));
    char       *cb = NameStr(*DatumGetName(b));

    return strncmp(ca, cb, NAMEDATALEN) == 0;
}

static uint32
namehashfast(Datum datum)
{
    char       *key = NameStr(*DatumGetName(datum));

    return hash_any((unsigned char *) key, strlen(key));
}

static bool
int2eqfast(Datum a, Datum b)
{
    return DatumGetInt16(a) == DatumGetInt16(b);
}

static uint32
int2hashfast(Datum datum)
{
    return murmurhash32((int32) DatumGetInt16(datum));
}

static bool
int4eqfast(Datum a, Datum b)
{
    return DatumGetInt32(a) == DatumGetInt32(b);
}

static uint32
int4hashfast(Datum datum)
{
    return murmurhash32((int32) DatumGetInt32(datum));
}

static bool
texteqfast(Datum a, Datum b)
{
    /*
     * The use of DEFAULT_COLLATION_OID is fairly arbitrary here.  We just
     * want to take the fast "deterministic" path in texteq().
     */
    return DatumGetBool(DirectFunctionCall2Coll(texteq, DEFAULT_COLLATION_OID, a, b));
}

static uint32
texthashfast(Datum datum)
{
    /* analogously here as in texteqfast() */
    return DatumGetInt32(DirectFunctionCall1Coll(hashtext, DEFAULT_COLLATION_OID, datum));
}

static bool
oidvectoreqfast(Datum a, Datum b)
{
    return DatumGetBool(DirectFunctionCall2(oidvectoreq, a, b));
}

static uint32
oidvectorhashfast(Datum datum)
{
    return DatumGetInt32(DirectFunctionCall1(hashoidvector, datum));
}

/* Lookup support functions for a type. */
static void
GetCCHashEqFuncs(Oid keytype, CCHashFN *hashfunc, RegProcedure *eqfunc, CCFastEqualFN *fasteqfunc)
{
    switch (keytype)
    {
        case BOOLOID:
            *hashfunc = charhashfast;
            *fasteqfunc = chareqfast;
            *eqfunc = F_BOOLEQ;
            break;
        case CHAROID:
            *hashfunc = charhashfast;
            *fasteqfunc = chareqfast;
            *eqfunc = F_CHAREQ;
            break;
        case NAMEOID:
            *hashfunc = namehashfast;
            *fasteqfunc = nameeqfast;
            *eqfunc = F_NAMEEQ;
            break;
        case INT2OID:
            *hashfunc = int2hashfast;
            *fasteqfunc = int2eqfast;
            *eqfunc = F_INT2EQ;
            break;
        case INT4OID:
            *hashfunc = int4hashfast;
            *fasteqfunc = int4eqfast;
            *eqfunc = F_INT4EQ;
            break;
        case TEXTOID:
            *hashfunc = texthashfast;
            *fasteqfunc = texteqfast;
            *eqfunc = F_TEXTEQ;
            break;
        case OIDOID:
        case REGPROCOID:
        case REGPROCEDUREOID:
        case REGOPEROID:
        case REGOPERATOROID:
        case REGCLASSOID:
        case REGTYPEOID:
        case REGCONFIGOID:
        case REGDICTIONARYOID:
        case REGROLEOID:
        case REGNAMESPACEOID:
            *hashfunc = int4hashfast;
            *fasteqfunc = int4eqfast;
            *eqfunc = F_OIDEQ;
            break;
        case OIDVECTOROID:
            *hashfunc = oidvectorhashfast;
            *fasteqfunc = oidvectoreqfast;
            *eqfunc = F_OIDVECTOREQ;
            break;
        default:
            elog(FATAL, "type %u not supported as catcache key", keytype);
            *hashfunc = NULL;   /* keep compiler quiet */

            *eqfunc = InvalidOid;
            break;
    }
}

/*
 *      CatalogCacheComputeHashValue
 *
 * Compute the hash value associated with a given set of lookup keys
 */
static uint32
CatalogCacheComputeHashValue(CatCache *cache, int nkeys,
                             Datum v1, Datum v2, Datum v3, Datum v4)
{
    uint32      hashValue = 0;
    uint32      oneHash;
    CCHashFN   *cc_hashfunc = cache->cc_hashfunc;

    CACHE_elog(DEBUG2, "CatalogCacheComputeHashValue %s %d %p",
               cache->cc_relname, nkeys, cache);

    switch (nkeys)
    {
        case 4:
            oneHash = (cc_hashfunc[3]) (v4);

            hashValue ^= oneHash << 24;
            hashValue ^= oneHash >> 8;
            /* FALLTHROUGH */
        case 3:
            oneHash = (cc_hashfunc[2]) (v3);

            hashValue ^= oneHash << 16;
            hashValue ^= oneHash >> 16;
            /* FALLTHROUGH */
        case 2:
            oneHash = (cc_hashfunc[1]) (v2);

            hashValue ^= oneHash << 8;
            hashValue ^= oneHash >> 24;
            /* FALLTHROUGH */
        case 1:
            oneHash = (cc_hashfunc[0]) (v1);

            hashValue ^= oneHash;
            break;
        default:
            elog(FATAL, "wrong number of hash keys: %d", nkeys);
            break;
    }

    return hashValue;
}

/*
 *      CatalogCacheComputeTupleHashValue
 *
 * Compute the hash value associated with a given tuple to be cached
 */
static uint32
CatalogCacheComputeTupleHashValue(CatCache *cache, int nkeys, HeapTuple tuple)
{
    Datum       v1 = 0,
                v2 = 0,
                v3 = 0,
                v4 = 0;
    bool        isNull = false;
    int        *cc_keyno = cache->cc_keyno;
    TupleDesc   cc_tupdesc = cache->cc_tupdesc;

    /* Now extract key fields from tuple, insert into scankey */
    switch (nkeys)
    {
        case 4:
            v4 = fastgetattr(tuple,
                             cc_keyno[3],
                             cc_tupdesc,
                             &isNull);
            Assert(!isNull);
            /* FALLTHROUGH */
        case 3:
            v3 = fastgetattr(tuple,
                             cc_keyno[2],
                             cc_tupdesc,
                             &isNull);
            Assert(!isNull);
            /* FALLTHROUGH */
        case 2:
            v2 = fastgetattr(tuple,
                             cc_keyno[1],
                             cc_tupdesc,
                             &isNull);
            Assert(!isNull);
            /* FALLTHROUGH */
        case 1:
            v1 = fastgetattr(tuple,
                             cc_keyno[0],
                             cc_tupdesc,
                             &isNull);
            Assert(!isNull);
            break;
        default:
            elog(FATAL, "wrong number of hash keys: %d", nkeys);
            break;
    }

    return CatalogCacheComputeHashValue(cache, nkeys, v1, v2, v3, v4);
}

/*
 *      CatalogCacheCompareTuple
 *
 * Compare a tuple to the passed arguments.
 */
static inline bool
CatalogCacheCompareTuple(const CatCache *cache, int nkeys,
                         const Datum *cachekeys,
                         const Datum *searchkeys)
{
    const CCFastEqualFN *cc_fastequal = cache->cc_fastequal;
    int         i;

    for (i = 0; i < nkeys; i++)
    {
        if (!(cc_fastequal[i]) (cachekeys[i], searchkeys[i]))
            return false;
    }
    return true;
}


#ifdef CATCACHE_STATS

static void
CatCachePrintStats(int code, Datum arg)
{
    slist_iter  iter;
    long        cc_searches = 0;
    long        cc_hits = 0;
    long        cc_neg_hits = 0;
    long        cc_newloads = 0;
    long        cc_invals = 0;
    long        cc_lsearches = 0;
    long        cc_lhits = 0;

    slist_foreach(iter, &CacheHdr->ch_caches)
    {
        CatCache   *cache = slist_container(CatCache, cc_next, iter.cur);

        if (cache->cc_ntup == 0 && cache->cc_searches == 0)
            continue;           /* don't print unused caches */
        elog(DEBUG2, "catcache %s/%u: %d tup, %ld srch, %ld+%ld=%ld hits, %ld+%ld=%ld loads, %ld invals, %ld lsrch, %ld lhits",
             cache->cc_relname,
             cache->cc_indexoid,
             cache->cc_ntup,
             cache->cc_searches,
             cache->cc_hits,
             cache->cc_neg_hits,
             cache->cc_hits + cache->cc_neg_hits,
             cache->cc_newloads,
             cache->cc_searches - cache->cc_hits - cache->cc_neg_hits - cache->cc_newloads,
             cache->cc_searches - cache->cc_hits - cache->cc_neg_hits,
             cache->cc_invals,
             cache->cc_lsearches,
             cache->cc_lhits);
        cc_searches += cache->cc_searches;
        cc_hits += cache->cc_hits;
        cc_neg_hits += cache->cc_neg_hits;
        cc_newloads += cache->cc_newloads;
        cc_invals += cache->cc_invals;
        cc_lsearches += cache->cc_lsearches;
        cc_lhits += cache->cc_lhits;
    }
    elog(DEBUG2, "catcache totals: %d tup, %ld srch, %ld+%ld=%ld hits, %ld+%ld=%ld loads, %ld invals, %ld lsrch, %ld lhits",
         CacheHdr->ch_ntup,
         cc_searches,
         cc_hits,
         cc_neg_hits,
         cc_hits + cc_neg_hits,
         cc_newloads,
         cc_searches - cc_hits - cc_neg_hits - cc_newloads,
         cc_searches - cc_hits - cc_neg_hits,
         cc_invals,
         cc_lsearches,
         cc_lhits);
}
#endif                          /* CATCACHE_STATS */


/*
 *      CatCacheRemoveCTup
 *
 * Unlink and delete the given cache entry
 *
 * NB: if it is a member of a CatCList, the CatCList is deleted too.
 * Both the cache entry and the list had better have zero refcount.
 */
static void
CatCacheRemoveCTup(CatCache *cache, CatCTup *ct)
{
    Assert(ct->refcount == 0);
    Assert(ct->my_cache == cache);

    if (ct->c_list)
    {
        /*
         * The cleanest way to handle this is to call CatCacheRemoveCList,
         * which will recurse back to me, and the recursive call will do the
         * work.  Set the "dead" flag to make sure it does recurse.
         */
        ct->dead = true;
        CatCacheRemoveCList(cache, ct->c_list);
        return;                 /* nothing left to do */
    }

    /* delink from linked list */
    dlist_delete(&ct->cache_elem);

    /*
     * Free keys when we're dealing with a negative entry, normal entries just
     * point into tuple, allocated together with the CatCTup.
     */
    if (ct->negative)
        CatCacheFreeKeys(cache->cc_tupdesc, cache->cc_nkeys,
                         cache->cc_keyno, ct->keys);

    pfree(ct);

    --cache->cc_ntup;
    --CacheHdr->ch_ntup;
}

/*
 *      CatCacheRemoveCList
 *
 * Unlink and delete the given cache list entry
 *
 * NB: any dead member entries that become unreferenced are deleted too.
 */
static void
CatCacheRemoveCList(CatCache *cache, CatCList *cl)
{
    int         i;

    Assert(cl->refcount == 0);
    Assert(cl->my_cache == cache);

    /* delink from member tuples */
    for (i = cl->n_members; --i >= 0;)
    {
        CatCTup    *ct = cl->members[i];

        Assert(ct->c_list == cl);
        ct->c_list = NULL;
        /* if the member is dead and now has no references, remove it */
        if (
#ifndef CATCACHE_FORCE_RELEASE
            ct->dead &&
#endif
            ct->refcount == 0)
            CatCacheRemoveCTup(cache, ct);
    }

    /* delink from linked list */
    dlist_delete(&cl->cache_elem);

    /* free associated column data */
    CatCacheFreeKeys(cache->cc_tupdesc, cl->nkeys,
                     cache->cc_keyno, cl->keys);

    pfree(cl);
}


/*
 *  CatCacheInvalidate
 *
 *  Invalidate entries in the specified cache, given a hash value.
 *
 *  We delete cache entries that match the hash value, whether positive
 *  or negative.  We don't care whether the invalidation is the result
 *  of a tuple insertion or a deletion.
 *
 *  We used to try to match positive cache entries by TID, but that is
 *  unsafe after a VACUUM FULL on a system catalog: an inval event could
 *  be queued before VACUUM FULL, and then processed afterwards, when the
 *  target tuple that has to be invalidated has a different TID than it
 *  did when the event was created.  So now we just compare hash values and
 *  accept the small risk of unnecessary invalidations due to false matches.
 *
 *  This routine is only quasi-public: it should only be used by inval.c.
 */
void
CatCacheInvalidate(CatCache *cache, uint32 hashValue)
{
    Index       hashIndex;
    dlist_mutable_iter iter;

    CACHE_elog(DEBUG2, "CatCacheInvalidate: called");

    /*
     * We don't bother to check whether the cache has finished initialization
     * yet; if not, there will be no entries in it so no problem.
     */

    /*
     * Invalidate *all* CatCLists in this cache; it's too hard to tell which
     * searches might still be correct, so just zap 'em all.
     */
    dlist_foreach_modify(iter, &cache->cc_lists)
    {
        CatCList   *cl = dlist_container(CatCList, cache_elem, iter.cur);

        if (cl->refcount > 0)
            cl->dead = true;
        else
            CatCacheRemoveCList(cache, cl);
    }

    /*
     * inspect the proper hash bucket for tuple matches
     */
    hashIndex = HASH_INDEX(hashValue, cache->cc_nbuckets);
    dlist_foreach_modify(iter, &cache->cc_bucket[hashIndex])
    {
        CatCTup    *ct = dlist_container(CatCTup, cache_elem, iter.cur);

        if (hashValue == ct->hash_value)
        {
            if (ct->refcount > 0 ||
                (ct->c_list && ct->c_list->refcount > 0))
            {
                ct->dead = true;
                /* list, if any, was marked dead above */
                Assert(ct->c_list == NULL || ct->c_list->dead);
            }
            else
                CatCacheRemoveCTup(cache, ct);
            CACHE_elog(DEBUG2, "CatCacheInvalidate: invalidated");
#ifdef CATCACHE_STATS
            cache->cc_invals++;
#endif
            /* could be multiple matches, so keep looking! */
        }
    }
}

/* ----------------------------------------------------------------
 *                     public functions
 * ----------------------------------------------------------------
 */


/*
 * Standard routine for creating cache context if it doesn't exist yet
 *
 * There are a lot of places (probably far more than necessary) that check
 * whether CacheMemoryContext exists yet and want to create it if not.
 * We centralize knowledge of exactly how to create it here.
 */
void
CreateCacheMemoryContext(void)
{
    /*
     * Purely for paranoia, check that context doesn't exist; caller probably
     * did so already.
     */
    if (!CacheMemoryContext)
        CacheMemoryContext = AllocSetContextCreate(TopMemoryContext,
                                                   "CacheMemoryContext",
                                                   ALLOCSET_DEFAULT_SIZES);
}


/*
 *      ResetCatalogCache
 *
 * Reset one catalog cache to empty.
 *
 * This is not very efficient if the target cache is nearly empty.
 * However, it shouldn't need to be efficient; we don't invoke it often.
 */
static void
ResetCatalogCache(CatCache *cache)
{
    dlist_mutable_iter iter;
    int         i;

    /* Remove each list in this cache, or at least mark it dead */
    dlist_foreach_modify(iter, &cache->cc_lists)
    {
        CatCList   *cl = dlist_container(CatCList, cache_elem, iter.cur);

        if (cl->refcount > 0)
            cl->dead = true;
        else
            CatCacheRemoveCList(cache, cl);
    }

    /* Remove each tuple in this cache, or at least mark it dead */
    for (i = 0; i < cache->cc_nbuckets; i++)
    {
        dlist_head *bucket = &cache->cc_bucket[i];

        dlist_foreach_modify(iter, bucket)
        {
            CatCTup    *ct = dlist_container(CatCTup, cache_elem, iter.cur);

            if (ct->refcount > 0 ||
                (ct->c_list && ct->c_list->refcount > 0))
            {
                ct->dead = true;
                /* list, if any, was marked dead above */
                Assert(ct->c_list == NULL || ct->c_list->dead);
            }
            else
                CatCacheRemoveCTup(cache, ct);
#ifdef CATCACHE_STATS
            cache->cc_invals++;
#endif
        }
    }
}

/*
 *      ResetCatalogCaches
 *
 * Reset all caches when a shared cache inval event forces it
 */
void
ResetCatalogCaches(void)
{
    slist_iter  iter;

    CACHE_elog(DEBUG2, "ResetCatalogCaches called");

    slist_foreach(iter, &CacheHdr->ch_caches)
    {
        CatCache   *cache = slist_container(CatCache, cc_next, iter.cur);

        ResetCatalogCache(cache);
    }

    CACHE_elog(DEBUG2, "end of ResetCatalogCaches call");
}

/*
 *      CatalogCacheFlushCatalog
 *
 *  Flush all catcache entries that came from the specified system catalog.
 *  This is needed after VACUUM FULL/CLUSTER on the catalog, since the
 *  tuples very likely now have different TIDs than before.  (At one point
 *  we also tried to force re-execution of CatalogCacheInitializeCache for
 *  the cache(s) on that catalog.  This is a bad idea since it leads to all
 *  kinds of trouble if a cache flush occurs while loading cache entries.
 *  We now avoid the need to do it by copying cc_tupdesc out of the relcache,
 *  rather than relying on the relcache to keep a tupdesc for us.  Of course
 *  this assumes the tupdesc of a cachable system table will not change...)
 */
void
CatalogCacheFlushCatalog(Oid catId)
{
    slist_iter  iter;

    CACHE_elog(DEBUG2, "CatalogCacheFlushCatalog called for %u", catId);

    slist_foreach(iter, &CacheHdr->ch_caches)
    {
        CatCache   *cache = slist_container(CatCache, cc_next, iter.cur);

        /* Does this cache store tuples of the target catalog? */
        if (cache->cc_reloid == catId)
        {
            /* Yes, so flush all its contents */
            ResetCatalogCache(cache);

            /* Tell inval.c to call syscache callbacks for this cache */
            CallSyscacheCallbacks(cache->id, 0);
        }
    }

    CACHE_elog(DEBUG2, "end of CatalogCacheFlushCatalog call");
}

/*
 *      InitCatCache
 *
 *  This allocates and initializes a cache for a system catalog relation.
 *  Actually, the cache is only partially initialized to avoid opening the
 *  relation.  The relation will be opened and the rest of the cache
 *  structure initialized on the first access.
 */
#ifdef CACHEDEBUG
#define InitCatCache_DEBUG2 \
do { \
    elog(DEBUG2, "InitCatCache: rel=%u ind=%u id=%d nkeys=%d size=%d", \
         cp->cc_reloid, cp->cc_indexoid, cp->id, \
         cp->cc_nkeys, cp->cc_nbuckets); \
} while(0)
#else
#define InitCatCache_DEBUG2
#endif

CatCache *
InitCatCache(int id,
             Oid reloid,
             Oid indexoid,
             int nkeys,
             const int *key,
             int nbuckets)
{
    CatCache   *cp;
    MemoryContext oldcxt;
    size_t      sz;
    int         i;

    /*
     * nbuckets is the initial number of hash buckets to use in this catcache.
     * It will be enlarged later if it becomes too full.
     *
     * nbuckets must be a power of two.  We check this via Assert rather than
     * a full runtime check because the values will be coming from constant
     * tables.
     *
     * If you're confused by the power-of-two check, see comments in
     * bitmapset.c for an explanation.
     */
    Assert(nbuckets > 0 && (nbuckets & -nbuckets) == nbuckets);

    /*
     * first switch to the cache context so our allocations do not vanish at
     * the end of a transaction
     */
    if (!CacheMemoryContext)
        CreateCacheMemoryContext();

    oldcxt = MemoryContextSwitchTo(CacheMemoryContext);

    /*
     * if first time through, initialize the cache group header
     */
    if (CacheHdr == NULL)
    {
        CacheHdr = (CatCacheHeader *) palloc(sizeof(CatCacheHeader));
        slist_init(&CacheHdr->ch_caches);
        CacheHdr->ch_ntup = 0;
#ifdef CATCACHE_STATS
        /* set up to dump stats at backend exit */
        on_proc_exit(CatCachePrintStats, 0);
#endif
    }

    /*
     * Allocate a new cache structure, aligning to a cacheline boundary
     *
     * Note: we rely on zeroing to initialize all the dlist headers correctly
     */
    sz = sizeof(CatCache) + PG_CACHE_LINE_SIZE;
    cp = (CatCache *) CACHELINEALIGN(palloc0(sz));
    cp->cc_bucket = palloc0(nbuckets * sizeof(dlist_head));

    /*
     * initialize the cache's relation information for the relation
     * corresponding to this cache, and initialize some of the new cache's
     * other internal fields.  But don't open the relation yet.
     */
    cp->id = id;
    cp->cc_relname = "(not known yet)";
    cp->cc_reloid = reloid;
    cp->cc_indexoid = indexoid;
    cp->cc_relisshared = false; /* temporary */
    cp->cc_tupdesc = (TupleDesc) NULL;
    cp->cc_ntup = 0;
    cp->cc_nbuckets = nbuckets;
    cp->cc_nkeys = nkeys;
    for (i = 0; i < nkeys; ++i)
        cp->cc_keyno[i] = key[i];

    /*
     * new cache is initialized as far as we can go for now. print some
     * debugging information, if appropriate.
     */
    InitCatCache_DEBUG2;

    /*
     * add completed cache to top of group header's list
     */
    slist_push_head(&CacheHdr->ch_caches, &cp->cc_next);

    /*
     * back to the old context before we return...
     */
    MemoryContextSwitchTo(oldcxt);

    return cp;
}

/*
 * Enlarge a catcache, doubling the number of buckets.
 */
static void
RehashCatCache(CatCache *cp)
{
    dlist_head *newbucket;
    int         newnbuckets;
    int         i;

    elog(DEBUG1, "rehashing catalog cache id %d for %s; %d tups, %d buckets",
         cp->id, cp->cc_relname, cp->cc_ntup, cp->cc_nbuckets);

    /* Allocate a new, larger, hash table. */
    newnbuckets = cp->cc_nbuckets * 2;
    newbucket = (dlist_head *) MemoryContextAllocZero(CacheMemoryContext, newnbuckets * sizeof(dlist_head));

    /* Move all entries from old hash table to new. */
    for (i = 0; i < cp->cc_nbuckets; i++)
    {
        dlist_mutable_iter iter;

        dlist_foreach_modify(iter, &cp->cc_bucket[i])
        {
            CatCTup    *ct = dlist_container(CatCTup, cache_elem, iter.cur);
            int         hashIndex = HASH_INDEX(ct->hash_value, newnbuckets);

            dlist_delete(iter.cur);
            dlist_push_head(&newbucket[hashIndex], &ct->cache_elem);
        }
    }

    /* Switch to the new array. */
    pfree(cp->cc_bucket);
    cp->cc_nbuckets = newnbuckets;
    cp->cc_bucket = newbucket;
}

/*
 *      CatalogCacheInitializeCache
 *
 * This function does final initialization of a catcache: obtain the tuple
 * descriptor and set up the hash and equality function links.  We assume
 * that the relcache entry can be opened at this point!
 */
#ifdef CACHEDEBUG
#define CatalogCacheInitializeCache_DEBUG1 \
    elog(DEBUG2, "CatalogCacheInitializeCache: cache @%p rel=%u", cache, \
         cache->cc_reloid)

#define CatalogCacheInitializeCache_DEBUG2 \
do { \
        if (cache->cc_keyno[i] > 0) { \
            elog(DEBUG2, "CatalogCacheInitializeCache: load %d/%d w/%d, %u", \
                i+1, cache->cc_nkeys, cache->cc_keyno[i], \
                 TupleDescAttr(tupdesc, cache->cc_keyno[i] - 1)->atttypid); \
        } else { \
            elog(DEBUG2, "CatalogCacheInitializeCache: load %d/%d w/%d", \
                i+1, cache->cc_nkeys, cache->cc_keyno[i]); \
        } \
} while(0)
#else
#define CatalogCacheInitializeCache_DEBUG1
#define CatalogCacheInitializeCache_DEBUG2
#endif

static void
CatalogCacheInitializeCache(CatCache *cache)
{
    Relation    relation;
    MemoryContext oldcxt;
    TupleDesc   tupdesc;
    int         i;

    CatalogCacheInitializeCache_DEBUG1;

    relation = table_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);

    table_close(relation, AccessShareLock);

    CACHE_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_keyno[i] > 0)
        {
            Form_pg_attribute attr = TupleDescAttr(tupdesc,
                                                   cache->cc_keyno[i] - 1);

            keytype = attr->atttypid;
            /* cache key columns should always be NOT NULL */
            Assert(attr->attnotnull);
        }
        else
        {
            if (cache->cc_keyno[i] < 0)
                elog(FATAL, "sys attributes are not supported in caches");
            keytype = OIDOID;
        }

        GetCCHashEqFuncs(keytype,
                         &cache->cc_hashfunc[i],
                         &eqfunc,
                         &cache->cc_fastequal[i]);

        /*
         * 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_keyno[i];

        /* Fill in sk_strategy as well --- always standard equality */
        cache->cc_skey[i].sk_strategy = BTEqualStrategyNumber;
        cache->cc_skey[i].sk_subtype = InvalidOid;
        /* If a catcache key requires a collation, it must be C collation */
        cache->cc_skey[i].sk_collation = C_COLLATION_OID;

        CACHE_elog(DEBUG2, "CatalogCacheInitializeCache %s %d %p",
                   cache->cc_relname, i, cache);
    }

    /*
     * mark this cache fully initialized
     */
    cache->cc_tupdesc = tupdesc;
}

/*
 * InitCatCachePhase2 -- external interface for CatalogCacheInitializeCache
 *
 * One reason to call this routine is to ensure that the relcache has
 * created entries for all the catalogs and indexes referenced by catcaches.
 * Therefore, provide an option to open the index as well as fixing the
 * cache itself.  An exception is the indexes on pg_am, which we don't use
 * (cf. IndexScanOK).
 */
void
InitCatCachePhase2(CatCache *cache, bool touch_index)
{
    if (cache->cc_tupdesc == NULL)
        CatalogCacheInitializeCache(cache);

    if (touch_index &&
        cache->id != AMOID &&
        cache->id != AMNAME)
    {
        Relation    idesc;

        /*
         * We must lock the underlying catalog before opening the index to
         * avoid deadlock, since index_open could possibly result in reading
         * this same catalog, and if anyone else is exclusive-locking this
         * catalog and index they'll be doing it in that order.
         */
        LockRelationOid(cache->cc_reloid, AccessShareLock);
        idesc = index_open(cache->cc_indexoid, AccessShareLock);

        /*
         * While we've got the index open, let's check that it's unique (and
         * not just deferrable-unique, thank you very much).  This is just to
         * catch thinkos in definitions of new catcaches, so we don't worry
         * about the pg_am indexes not getting tested.
         */
        Assert(idesc->rd_index->indisunique &&
               idesc->rd_index->indimmediate);

        index_close(idesc, AccessShareLock);
        UnlockRelationOid(cache->cc_reloid, AccessShareLock);
    }
}


/*
 *      IndexScanOK
 *
 *      This function checks for tuples that will be fetched by
 *      IndexSupportInitialize() during relcache initialization for
 *      certain system indexes that support critical syscaches.
 *      We can't use an indexscan to fetch these, else we'll get into
 *      infinite recursion.  A plain heap scan will work, however.
 *      Once we have completed relcache initialization (signaled by
 *      criticalRelcachesBuilt), we don't have to worry anymore.
 *
 *      Similarly, during backend startup we have to be able to use the
 *      pg_authid and pg_auth_members syscaches for authentication even if
 *      we don't yet have relcache entries for those catalogs' indexes.
 */
static bool
IndexScanOK(CatCache *cache, ScanKey cur_skey)
{
    switch (cache->id)
    {
        case INDEXRELID:

            /*
             * Rather than tracking exactly which indexes have to be loaded
             * before we can use indexscans (which changes from time to time),
             * just force all pg_index searches to be heap scans until we've
             * built the critical relcaches.
             */
            if (!criticalRelcachesBuilt)
                return false;
            break;

        case AMOID:
        case AMNAME:

            /*
             * Always do heap scans in pg_am, because it's so small there's
             * not much point in an indexscan anyway.  We *must* do this when
             * initially building critical relcache entries, but we might as
             * well just always do it.
             */
            return false;

        case AUTHNAME:
        case AUTHOID:
        case AUTHMEMMEMROLE:

            /*
             * Protect authentication lookups occurring before relcache has
             * collected entries for shared indexes.
             */
            if (!criticalSharedRelcachesBuilt)
                return false;
            break;

        default:
            break;
    }

    /* Normal case, allow index scan */
    return true;
}

/*
 *  SearchCatCacheInternal
 *
 *      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)
{
    return SearchCatCacheInternal(cache, cache->cc_nkeys, v1, v2, v3, v4);
}


/*
 * SearchCatCacheN() are SearchCatCache() versions for a specific number of
 * arguments. The compiler can inline the body and unroll loops, making them a
 * bit faster than SearchCatCache().
 */

HeapTuple
SearchCatCache1(CatCache *cache,
                Datum v1)
{
    return SearchCatCacheInternal(cache, 1, v1, 0, 0, 0);
}


HeapTuple
SearchCatCache2(CatCache *cache,
                Datum v1, Datum v2)
{
    return SearchCatCacheInternal(cache, 2, v1, v2, 0, 0);
}


HeapTuple
SearchCatCache3(CatCache *cache,
                Datum v1, Datum v2, Datum v3)
{
    return SearchCatCacheInternal(cache, 3, v1, v2, v3, 0);
}


HeapTuple
SearchCatCache4(CatCache *cache,
                Datum v1, Datum v2, Datum v3, Datum v4)
{
    return SearchCatCacheInternal(cache, 4, v1, v2, v3, v4);
}

/*
 * Work-horse for SearchCatCache/SearchCatCacheN.
 */
static inline HeapTuple
SearchCatCacheInternal(CatCache *cache,
                       int nkeys,
                       Datum v1,
                       Datum v2,
                       Datum v3,
                       Datum v4)
{
    Datum       arguments[CATCACHE_MAXKEYS];
    uint32      hashValue;
    Index       hashIndex;
    dlist_iter  iter;
    dlist_head *bucket;
    CatCTup    *ct;

    /* Make sure we're in an xact, even if this ends up being a cache hit */
    Assert(IsTransactionState());

    Assert(cache->cc_nkeys == nkeys);

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

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

    /* Initialize local parameter array */
    arguments[0] = v1;
    arguments[1] = v2;
    arguments[2] = v3;
    arguments[3] = v4;

    /*
     * find the hash bucket in which to look for the tuple
     */
    hashValue = CatalogCacheComputeHashValue(cache, nkeys, v1, v2, v3, v4);
    hashIndex = HASH_INDEX(hashValue, cache->cc_nbuckets);

    /*
     * scan the hash bucket until we find a match or exhaust our tuples
     *
     * Note: it's okay to use dlist_foreach here, even though we modify the
     * dlist within the loop, because we don't continue the loop afterwards.
     */
    bucket = &cache->cc_bucket[hashIndex];
    dlist_foreach(iter, bucket)
    {
        ct = dlist_container(CatCTup, cache_elem, iter.cur);

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

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

        if (!CatalogCacheCompareTuple(cache, nkeys, ct->keys, arguments))
            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.)
         */
        dlist_move_head(bucket, &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);

            CACHE_elog(DEBUG2, "SearchCatCache(%s): found in bucket %d",
                       cache->cc_relname, hashIndex);

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

            return &ct->tuple;
        }
        else
        {
            CACHE_elog(DEBUG2, "SearchCatCache(%s): found neg entry in bucket %d",
                       cache->cc_relname, hashIndex);

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

            return NULL;
        }
    }

    return SearchCatCacheMiss(cache, nkeys, hashValue, hashIndex, v1, v2, v3, v4);
}

/*
 * Search the actual catalogs, rather than the cache.
 *
 * This is kept separate from SearchCatCacheInternal() to keep the fast-path
 * as small as possible.  To avoid that effort being undone by a helpful
 * compiler, try to explicitly forbid inlining.
 */
static pg_noinline HeapTuple
SearchCatCacheMiss(CatCache *cache,
                   int nkeys,
                   uint32 hashValue,
                   Index hashIndex,
                   Datum v1,
                   Datum v2,
                   Datum v3,
                   Datum v4)
{
    ScanKeyData cur_skey[CATCACHE_MAXKEYS];
    Relation    relation;
    SysScanDesc scandesc;
    HeapTuple   ntp;
    CatCTup    *ct;
    Datum       arguments[CATCACHE_MAXKEYS];

    /* Initialize local parameter array */
    arguments[0] = v1;
    arguments[1] = v2;
    arguments[2] = v3;
    arguments[3] = v4;

    /*
     * Ok, need to make a lookup in the relation, copy the scankey and fill
     * out any per-call fields.
     */
    memcpy(cur_skey, cache->cc_skey, sizeof(ScanKeyData) * nkeys);
    cur_skey[0].sk_argument = v1;
    cur_skey[1].sk_argument = v2;
    cur_skey[2].sk_argument = v3;
    cur_skey[3].sk_argument = v4;

    /*
     * 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 table_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 = table_open(cache->cc_reloid, AccessShareLock);

    scandesc = systable_beginscan(relation,
                                  cache->cc_indexoid,
                                  IndexScanOK(cache, cur_skey),
                                  NULL,
                                  nkeys,
                                  cur_skey);

    ct = NULL;

    while (HeapTupleIsValid(ntp = systable_getnext(scandesc)))
    {
        ct = CatalogCacheCreateEntry(cache, ntp, arguments,
                                     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);

    table_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;

        ct = CatalogCacheCreateEntry(cache, NULL, arguments,
                                     hashValue, hashIndex,
                                     true);

        CACHE_elog(DEBUG2, "SearchCatCache(%s): Contains %d/%d tuples",
                   cache->cc_relname, cache->cc_ntup, CacheHdr->ch_ntup);
        CACHE_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;
    }

    CACHE_elog(DEBUG2, "SearchCatCache(%s): Contains %d/%d tuples",
               cache->cc_relname, cache->cc_ntup, CacheHdr->ch_ntup);
    CACHE_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--;
    ResourceOwnerForgetCatCacheRef(CurrentResourceOwner, &ct->tuple);

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


/*
 *  GetCatCacheHashValue
 *
 *      Compute the hash value for a given set of search keys.
 *
 * The reason for exposing this as part of the API is that the hash value is
 * exposed in cache invalidation operations, so there are places outside the
 * catcache code that need to be able to compute the hash values.
 */
uint32
GetCatCacheHashValue(CatCache *cache,
                     Datum v1,
                     Datum v2,
                     Datum v3,
                     Datum v4)
{
    /*
     * one-time startup overhead for each cache
     */
    if (cache->cc_tupdesc == NULL)
        CatalogCacheInitializeCache(cache);

    /*
     * calculate the hash value
     */
    return CatalogCacheComputeHashValue(cache, cache->cc_nkeys, v1, v2, v3, v4);
}


/*
 *  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).
 *
 *      It doesn't make any sense to specify all of the cache's key columns
 *      here: since the key is unique, there could be at most one match, so
 *      you ought to use SearchCatCache() instead.  Hence this function takes
 *      one less Datum argument than SearchCatCache() does.
 *
 *      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 = 0;         /* dummy last-column value */
    Datum       arguments[CATCACHE_MAXKEYS];
    uint32      lHashValue;
    dlist_iter  iter;
    CatCList   *cl;
    CatCTup    *ct;
    List       *volatile ctlist;
    ListCell   *ctlist_item;
    int         nmembers;
    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 local parameter array */
    arguments[0] = v1;
    arguments[1] = v2;
    arguments[2] = v3;
    arguments[3] = 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, v1, v2, v3, v4);

    /*
     * scan the items until we find a match or exhaust our list
     *
     * Note: it's okay to use dlist_foreach here, even though we modify the
     * dlist within the loop, because we don't continue the loop afterwards.
     */
    dlist_foreach(iter, &cache->cc_lists)
    {
        cl = dlist_container(CatCList, cache_elem, iter.cur);

        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;

        if (!CatalogCacheCompareTuple(cache, nkeys, cl->keys, arguments))
            continue;

        /*
         * We found a matching list.  Move the list 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.)
         */
        dlist_move_head(&cache->cc_lists, &cl->cache_elem);

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

        CACHE_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.
     *
     * 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();
    {
        ScanKeyData cur_skey[CATCACHE_MAXKEYS];
        Relation    relation;
        SysScanDesc scandesc;

        /*
         * Ok, need to make a lookup in the relation, copy the scankey and
         * fill out any per-call fields.
         */
        memcpy(cur_skey, cache->cc_skey, sizeof(ScanKeyData) * cache->cc_nkeys);
        cur_skey[0].sk_argument = v1;
        cur_skey[1].sk_argument = v2;
        cur_skey[2].sk_argument = v3;
        cur_skey[3].sk_argument = v4;

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

        scandesc = systable_beginscan(relation,
                                      cache->cc_indexoid,
                                      IndexScanOK(cache, cur_skey),
                                      NULL,
                                      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;
            bool        found = false;
            dlist_head *bucket;

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

            bucket = &cache->cc_bucket[hashIndex];
            dlist_foreach(iter, bucket)
            {
                ct = dlist_container(CatCTup, cache_elem, iter.cur);

                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 = true;
                break;          /* A-OK */
            }

            if (!found)
            {
                /* We didn't find a usable entry, so make a new one */
                ct = CatalogCacheCreateEntry(cache, ntp, arguments,
                                             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);

        table_close(relation, AccessShareLock);

        /* Now we can build the CatCList entry. */
        oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
        nmembers = list_length(ctlist);
        cl = (CatCList *)
            palloc(offsetof(CatCList, members) + nmembers * sizeof(CatCTup *));

        /* Extract key values */
        CatCacheCopyKeys(cache->cc_tupdesc, nkeys, cache->cc_keyno,
                         arguments, cl->keys);
        MemoryContextSwitchTo(oldcxt);

        /*
         * 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;
    cl->refcount = 0;           /* for the moment */
    cl->dead = false;
    cl->ordered = ordered;
    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);

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

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

    CACHE_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, Datum *arguments,
                        uint32 hashValue, Index hashIndex,
                        bool negative)
{
    CatCTup    *ct;
    HeapTuple   dtp;
    MemoryContext oldcxt;

    /* negative entries have no tuple associated */
    if (ntp)
    {
        int         i;

        Assert(!negative);

        /*
         * If there are any out-of-line toasted fields in the tuple, expand
         * them in-line.  This saves cycles during later use of the catcache
         * entry, and also protects us against the possibility of the toast
         * tuples being freed before we attempt to fetch them, in case of
         * something using a slightly stale catcache entry.
         */
        if (HeapTupleHasExternal(ntp))
            dtp = toast_flatten_tuple(ntp, cache->cc_tupdesc);
        else
            dtp = ntp;

        /* Allocate memory for CatCTup and the cached tuple in one go */
        oldcxt = MemoryContextSwitchTo(CacheMemoryContext);

        ct = (CatCTup *) palloc(sizeof(CatCTup) +
                                MAXIMUM_ALIGNOF + dtp->t_len);
        ct->tuple.t_len = dtp->t_len;
        ct->tuple.t_self = dtp->t_self;
        ct->tuple.t_tableOid = dtp->t_tableOid;
        ct->tuple.t_data = (HeapTupleHeader)
            MAXALIGN(((char *) ct) + sizeof(CatCTup));
        /* copy tuple contents */
        memcpy((char *) ct->tuple.t_data,
               (const char *) dtp->t_data,
               dtp->t_len);
        MemoryContextSwitchTo(oldcxt);

        if (dtp != ntp)
            heap_freetuple(dtp);

        /* extract keys - they'll point into the tuple if not by-value */
        for (i = 0; i < cache->cc_nkeys; i++)
        {
            Datum       atp;
            bool        isnull;

            atp = heap_getattr(&ct->tuple,
                               cache->cc_keyno[i],
                               cache->cc_tupdesc,
                               &isnull);
            Assert(!isnull);
            ct->keys[i] = atp;
        }
    }
    else
    {
        Assert(negative);
        oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
        ct = (CatCTup *) palloc(sizeof(CatCTup));

        /*
         * Store keys - they'll point into separately allocated memory if not
         * by-value.
         */
        CatCacheCopyKeys(cache->cc_tupdesc, cache->cc_nkeys, cache->cc_keyno,
                         arguments, ct->keys);
        MemoryContextSwitchTo(oldcxt);
    }

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

    dlist_push_head(&cache->cc_bucket[hashIndex], &ct->cache_elem);

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

    /*
     * If the hash table has become too full, enlarge the buckets array. Quite
     * arbitrarily, we enlarge when fill factor > 2.
     */
    if (cache->cc_ntup > cache->cc_nbuckets * 2)
        RehashCatCache(cache);

    return ct;
}

/*
 * Helper routine that frees keys stored in the keys array.
 */
static void
CatCacheFreeKeys(TupleDesc tupdesc, int nkeys, int *attnos, Datum *keys)
{
    int         i;

    for (i = 0; i < nkeys; i++)
    {
        int         attnum = attnos[i];
        Form_pg_attribute att;

        /* system attribute are not supported in caches */
        Assert(attnum > 0);

        att = TupleDescAttr(tupdesc, attnum - 1);

        if (!att->attbyval)
            pfree(DatumGetPointer(keys[i]));
    }
}

/*
 * Helper routine that copies the keys in the srckeys array into the dstkeys
 * one, guaranteeing that the datums are fully allocated in the current memory
 * context.
 */
static void
CatCacheCopyKeys(TupleDesc tupdesc, int nkeys, int *attnos,
                 Datum *srckeys, Datum *dstkeys)
{
    int         i;

    /*
     * XXX: memory and lookup performance could possibly be improved by
     * storing all keys in one allocation.
     */

    for (i = 0; i < nkeys; i++)
    {
        int         attnum = attnos[i];
        Form_pg_attribute att = TupleDescAttr(tupdesc, attnum - 1);
        Datum       src = srckeys[i];
        NameData    srcname;

        /*
         * 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 by datumCopy() could fall off the end
         * of memory.
         */
        if (att->atttypid == NAMEOID)
        {
            namestrcpy(&srcname, DatumGetCString(src));
            src = NameGetDatum(&srcname);
        }

        dstkeys[i] = datumCopy(src,
                               att->attbyval,
                               att->attlen);
    }

}

/*
 *  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 and hash value in inval.c's lists.
 *  SysCacheInvalidate will be called later, if appropriate,
 *  using the recorded information.
 *
 *  For an insert or delete, tuple is the target tuple and newtuple is NULL.
 *  For an update, we are called just once, with tuple being the old tuple
 *  version and newtuple the new version.  We should make two list entries
 *  if the tuple's hash value changed, but only one if it didn't.
 *
 *  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,
                              HeapTuple newtuple,
                              void (*function) (int, uint32, Oid))
{
    slist_iter  iter;
    Oid         reloid;

    CACHE_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(s) in this cache,
     *         and call the passed function to register the information.
     * ----------------
     */

    slist_foreach(iter, &CacheHdr->ch_caches)
    {
        CatCache   *ccp = slist_container(CatCache, cc_next, iter.cur);
        uint32      hashvalue;
        Oid         dbid;

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

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

        hashvalue = CatalogCacheComputeTupleHashValue(ccp, ccp->cc_nkeys, tuple);
        dbid = ccp->cc_relisshared ? (Oid) 0 : MyDatabaseId;

        (*function) (ccp->id, hashvalue, dbid);

        if (newtuple)
        {
            uint32      newhashvalue;

            newhashvalue = CatalogCacheComputeTupleHashValue(ccp, ccp->cc_nkeys, newtuple);

            if (newhashvalue != hashvalue)
                (*function) (ccp->id, newhashvalue, dbid);
        }
    }
}


/*
 * 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);
}