spccache.c

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/*-------------------------------------------------------------------------
 *
 * spccache.c
 *    Tablespace cache management.
 *
 * We cache the parsed version of spcoptions for each tablespace to avoid
 * needing to reparse on every lookup.  Right now, there doesn't appear to
 * be a measurable performance gain from doing this, but that might change
 * in the future as we add more options.
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/utils/cache/spccache.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/reloptions.h"
#include "catalog/pg_tablespace.h"
#include "commands/tablespace.h"
#include "miscadmin.h"
#include "optimizer/cost.h"
#include "utils/catcache.h"
#include "utils/hsearch.h"
#include "utils/inval.h"
#include "utils/spccache.h"
#include "utils/syscache.h"


/* Hash table for information about each tablespace */
static HTAB *TableSpaceCacheHash = NULL;

typedef struct
{
    Oid         oid;            /* lookup key - must be first */
    TableSpaceOpts *opts;       /* options, or NULL if none */
} TableSpaceCacheEntry;


/*
 * InvalidateTableSpaceCacheCallback
 *      Flush all cache entries when pg_tablespace is updated.
 *
 * When pg_tablespace is updated, we must flush the cache entry at least
 * for that tablespace.  Currently, we just flush them all.  This is quick
 * and easy and doesn't cost much, since there shouldn't be terribly many
 * tablespaces, nor do we expect them to be frequently modified.
 */
static void
InvalidateTableSpaceCacheCallback(Datum arg, int cacheid, uint32 hashvalue)
{
    HASH_SEQ_STATUS status;
    TableSpaceCacheEntry *spc;

    hash_seq_init(&status, TableSpaceCacheHash);
    while ((spc = (TableSpaceCacheEntry *) hash_seq_search(&status)) != NULL)
    {
        if (spc->opts)
            pfree(spc->opts);
        if (hash_search(TableSpaceCacheHash,
                        (void *) &spc->oid,
                        HASH_REMOVE,
                        NULL) == NULL)
            elog(ERROR, "hash table corrupted");
    }
}

/*
 * InitializeTableSpaceCache
 *      Initialize the tablespace cache.
 */
static void
InitializeTableSpaceCache(void)
{
    HASHCTL     ctl;

    /* Initialize the hash table. */
    MemSet(&ctl, 0, sizeof(ctl));
    ctl.keysize = sizeof(Oid);
    ctl.entrysize = sizeof(TableSpaceCacheEntry);
    ctl.hash = oid_hash;
    TableSpaceCacheHash =
        hash_create("TableSpace cache", 16, &ctl,
                    HASH_ELEM | HASH_FUNCTION);

    /* Make sure we've initialized CacheMemoryContext. */
    if (!CacheMemoryContext)
        CreateCacheMemoryContext();

    /* Watch for invalidation events. */
    CacheRegisterSyscacheCallback(TABLESPACEOID,
                                  InvalidateTableSpaceCacheCallback,
                                  (Datum) 0);
}

/*
 * get_tablespace
 *      Fetch TableSpaceCacheEntry structure for a specified table OID.
 *
 * Pointers returned by this function should not be stored, since a cache
 * flush will invalidate them.
 */
static TableSpaceCacheEntry *
get_tablespace(Oid spcid)
{
    TableSpaceCacheEntry *spc;
    HeapTuple   tp;
    TableSpaceOpts *opts;

    /*
     * Since spcid is always from a pg_class tuple, InvalidOid implies the
     * default.
     */
    if (spcid == InvalidOid)
        spcid = MyDatabaseTableSpace;

    /* Find existing cache entry, if any. */
    if (!TableSpaceCacheHash)
        InitializeTableSpaceCache();
    spc = (TableSpaceCacheEntry *) hash_search(TableSpaceCacheHash,
                                               (void *) &spcid,
                                               HASH_FIND,
                                               NULL);
    if (spc)
        return spc;

    /*
     * Not found in TableSpace cache.  Check catcache.  If we don't find a
     * valid HeapTuple, it must mean someone has managed to request tablespace
     * details for a non-existent tablespace.  We'll just treat that case as
     * if no options were specified.
     */
    tp = SearchSysCache1(TABLESPACEOID, ObjectIdGetDatum(spcid));
    if (!HeapTupleIsValid(tp))
        opts = NULL;
    else
    {
        Datum       datum;
        bool        isNull;

        datum = SysCacheGetAttr(TABLESPACEOID,
                                tp,
                                Anum_pg_tablespace_spcoptions,
                                &isNull);
        if (isNull)
            opts = NULL;
        else
        {
            bytea      *bytea_opts = tablespace_reloptions(datum, false);

            opts = MemoryContextAlloc(CacheMemoryContext, VARSIZE(bytea_opts));
            memcpy(opts, bytea_opts, VARSIZE(bytea_opts));
        }
        ReleaseSysCache(tp);
    }

    /*
     * Now create the cache entry.  It's important to do this only after
     * reading the pg_tablespace entry, since doing so could cause a cache
     * flush.
     */
    spc = (TableSpaceCacheEntry *) hash_search(TableSpaceCacheHash,
                                               (void *) &spcid,
                                               HASH_ENTER,
                                               NULL);
    spc->opts = opts;
    return spc;
}

/*
 * get_tablespace_page_costs
 *      Return random and/or sequential page costs for a given tablespace.
 */
void
get_tablespace_page_costs(Oid spcid,
                          double *spc_random_page_cost,
                          double *spc_seq_page_cost)
{
    TableSpaceCacheEntry *spc = get_tablespace(spcid);

    Assert(spc != NULL);

    if (spc_random_page_cost)
    {
        if (!spc->opts || spc->opts->random_page_cost < 0)
            *spc_random_page_cost = random_page_cost;
        else
            *spc_random_page_cost = spc->opts->random_page_cost;
    }

    if (spc_seq_page_cost)
    {
        if (!spc->opts || spc->opts->seq_page_cost < 0)
            *spc_seq_page_cost = seq_page_cost;
        else
            *spc_seq_page_cost = spc->opts->seq_page_cost;
    }
}