relfilenodemap.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * relfilenodemap.c
 *    relfilenode to oid mapping cache.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/utils/cache/relfilenodemap.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/htup_details.h"
#include "access/table.h"
#include "catalog/pg_class.h"
#include "catalog/pg_tablespace.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/catcache.h"
#include "utils/fmgroids.h"
#include "utils/hsearch.h"
#include "utils/inval.h"
#include "utils/rel.h"
#include "utils/relfilenodemap.h"
#include "utils/relmapper.h"

/* Hash table for information about each relfilenode <-> oid pair */
static HTAB *RelfilenodeMapHash = NULL;

/* built first time through in InitializeRelfilenodeMap */
static ScanKeyData relfilenode_skey[2];

typedef struct
{
    Oid         reltablespace;
    Oid         relfilenode;
} RelfilenodeMapKey;

typedef struct
{
    RelfilenodeMapKey key;      /* lookup key - must be first */
    Oid         relid;          /* pg_class.oid */
} RelfilenodeMapEntry;

/*
 * RelfilenodeMapInvalidateCallback
 *      Flush mapping entries when pg_class is updated in a relevant fashion.
 */
static void
RelfilenodeMapInvalidateCallback(Datum arg, Oid relid)
{
    HASH_SEQ_STATUS status;
    RelfilenodeMapEntry *entry;

    /* callback only gets registered after creating the hash */
    Assert(RelfilenodeMapHash != NULL);

    hash_seq_init(&status, RelfilenodeMapHash);
    while ((entry = (RelfilenodeMapEntry *) hash_seq_search(&status)) != NULL)
    {
        /*
         * If relid is InvalidOid, signaling a complete reset, we must remove
         * all entries, otherwise just remove the specific relation's entry.
         * Always remove negative cache entries.
         */
        if (relid == InvalidOid ||  /* complete reset */
            entry->relid == InvalidOid ||   /* negative cache entry */
            entry->relid == relid)  /* individual flushed relation */
        {
            if (hash_search(RelfilenodeMapHash,
                            (void *) &entry->key,
                            HASH_REMOVE,
                            NULL) == NULL)
                elog(ERROR, "hash table corrupted");
        }
    }
}

/*
 * InitializeRelfilenodeMap
 *      Initialize cache, either on first use or after a reset.
 */
static void
InitializeRelfilenodeMap(void)
{
    HASHCTL     ctl;
    int         i;

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

    /* build skey */
    MemSet(&relfilenode_skey, 0, sizeof(relfilenode_skey));

    for (i = 0; i < 2; i++)
    {
        fmgr_info_cxt(F_OIDEQ,
                      &relfilenode_skey[i].sk_func,
                      CacheMemoryContext);
        relfilenode_skey[i].sk_strategy = BTEqualStrategyNumber;
        relfilenode_skey[i].sk_subtype = InvalidOid;
        relfilenode_skey[i].sk_collation = InvalidOid;
    }

    relfilenode_skey[0].sk_attno = Anum_pg_class_reltablespace;
    relfilenode_skey[1].sk_attno = Anum_pg_class_relfilenode;

    /*
     * Only create the RelfilenodeMapHash now, so we don't end up partially
     * initialized when fmgr_info_cxt() above ERRORs out with an out of memory
     * error.
     */
    ctl.keysize = sizeof(RelfilenodeMapKey);
    ctl.entrysize = sizeof(RelfilenodeMapEntry);
    ctl.hcxt = CacheMemoryContext;

    RelfilenodeMapHash =
        hash_create("RelfilenodeMap cache", 64, &ctl,
                    HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);

    /* Watch for invalidation events. */
    CacheRegisterRelcacheCallback(RelfilenodeMapInvalidateCallback,
                                  (Datum) 0);
}

/*
 * Map a relation's (tablespace, filenode) to a relation's oid and cache the
 * result.
 *
 * Returns InvalidOid if no relation matching the criteria could be found.
 */
Oid
RelidByRelfilenode(Oid reltablespace, Oid relfilenode)
{
    RelfilenodeMapKey key;
    RelfilenodeMapEntry *entry;
    bool        found;
    SysScanDesc scandesc;
    Relation    relation;
    HeapTuple   ntp;
    ScanKeyData skey[2];
    Oid         relid;

    if (RelfilenodeMapHash == NULL)
        InitializeRelfilenodeMap();

    /* pg_class will show 0 when the value is actually MyDatabaseTableSpace */
    if (reltablespace == MyDatabaseTableSpace)
        reltablespace = 0;

    MemSet(&key, 0, sizeof(key));
    key.reltablespace = reltablespace;
    key.relfilenode = relfilenode;

    /*
     * Check cache and return entry if one is found. Even if no target
     * relation can be found later on we store the negative match and return a
     * InvalidOid from cache. That's not really necessary for performance
     * since querying invalid values isn't supposed to be a frequent thing,
     * but it's basically free.
     */
    entry = hash_search(RelfilenodeMapHash, (void *) &key, HASH_FIND, &found);

    if (found)
        return entry->relid;

    /* ok, no previous cache entry, do it the hard way */

    /* initialize empty/negative cache entry before doing the actual lookups */
    relid = InvalidOid;

    if (reltablespace == GLOBALTABLESPACE_OID)
    {
        /*
         * Ok, shared table, check relmapper.
         */
        relid = RelationMapFilenodeToOid(relfilenode, true);
    }
    else
    {
        /*
         * Not a shared table, could either be a plain relation or a
         * non-shared, nailed one, like e.g. pg_class.
         */

        /* check for plain relations by looking in pg_class */
        relation = table_open(RelationRelationId, AccessShareLock);

        /* copy scankey to local copy, it will be modified during the scan */
        memcpy(skey, relfilenode_skey, sizeof(skey));

        /* set scan arguments */
        skey[0].sk_argument = ObjectIdGetDatum(reltablespace);
        skey[1].sk_argument = ObjectIdGetDatum(relfilenode);

        scandesc = systable_beginscan(relation,
                                      ClassTblspcRelfilenodeIndexId,
                                      true,
                                      NULL,
                                      2,
                                      skey);

        found = false;

        while (HeapTupleIsValid(ntp = systable_getnext(scandesc)))
        {
            Form_pg_class classform = (Form_pg_class) GETSTRUCT(ntp);

            if (found)
                elog(ERROR,
                     "unexpected duplicate for tablespace %u, relfilenode %u",
                     reltablespace, relfilenode);
            found = true;

            Assert(classform->reltablespace == reltablespace);
            Assert(classform->relfilenode == relfilenode);
            relid = classform->oid;
        }

        systable_endscan(scandesc);
        table_close(relation, AccessShareLock);

        /* check for tables that are mapped but not shared */
        if (!found)
            relid = RelationMapFilenodeToOid(relfilenode, false);
    }

    /*
     * Only enter entry into cache now, our opening of pg_class could have
     * caused cache invalidations to be executed which would have deleted a
     * new entry if we had entered it above.
     */
    entry = hash_search(RelfilenodeMapHash, (void *) &key, HASH_ENTER, &found);
    if (found)
        elog(ERROR, "corrupted hashtable");
    entry->relid = relid;

    return relid;
}