Function lookupKeyReadWithFlags

src/db.cpp:160–201

Lookup a key for read operations, or return NULL if the key is not found * in the specified DB. * * As a side effect of calling this function: * 1. A key gets expired if it reached it's TTL. * 2. The key last access time is updated. * 3. The global keys hits/misses stats are updated (reported in INFO). * 4. If keyspace notifications are enabled, a "keymiss" notification is fired. * * This

 * correctly report a key is expired on slaves even if the master is lagging
 * expiring our key via DELs in the replication link. */
robj_roptr lookupKeyReadWithFlags(redisDb *db, robj *key, int flags) {
    robj_roptr val;

    if (expireIfNeeded(db,key) == 1) {
        /* If we are in the context of a master, expireIfNeeded() returns 1
         * when the key is no longer valid, so we can return NULL ASAP. */
        if (listLength(g_pserver->masters) == 0)
            goto keymiss;

        /* However if we are in the context of a replica, expireIfNeeded() will
         * not really try to expire the key, it only returns information
         * about the "logical" status of the key: key expiring is up to the
         * master in order to have a consistent view of master's data set.
         *
         * However, if the command caller is not the master, and as additional
         * safety measure, the command invoked is a read-only command, we can
         * safely return NULL here, and provide a more consistent behavior
         * to clients accessing expired values in a read-only fashion, that
         * will say the key as non existing.
         *
         * Notably this covers GETs when slaves are used to scale reads. */
        if (serverTL->current_client &&
            !FActiveMaster(serverTL->current_client) &&
            serverTL->current_client->cmd &&
            serverTL->current_client->cmd->flags & CMD_READONLY)
        {
            goto keymiss;
        }
    }
    val = lookupKeyConst(db,key,flags);
    if (val == nullptr)
        goto keymiss;
    g_pserver->stat_keyspace_hits++;
    return val;

keymiss:
    if (!(flags & LOOKUP_NONOTIFY)) {
        notifyKeyspaceEvent(NOTIFY_KEY_MISS, "keymiss", key, db->id);
    }
    g_pserver->stat_keyspace_misses++;
    return NULL;
}

/* Like lookupKeyReadWithFlags(), but does not use any flag, which is the
 * common case. */