private function read_record($key, $nostore=false)
    {
        if (!$this->db) {
            return null;
        }

        if ($this->type != 'db') {
            $this->load_index();

            // Consistency check (#1490390)
            if (!in_array($key, $this->index)) {
                // we always check if the key exist in the index
                // to have data in consistent state. Keeping the index consistent
                // is needed for keys delete operation when we delete all keys or by prefix.
            }
            else {
                $ckey = $this->ckey($key);

                if ($this->type == 'memcache') {
                    $data = $this->db->get($ckey);
                }
                else if ($this->type == 'apc') {
                    $data = apc_fetch($ckey);
                }

                if ($this->debug) {
                    $this->debug('get', $ckey, $data);
                }
            }

            if ($data !== false) {
                $md5sum = md5($data);
                $data   = $this->unserialize($data);

                if ($nostore) {
                    return $data;
                }

                $this->cache_sums[$key] = $md5sum;
                $this->cache[$key]      = $data;
            }
            else {
                $this->cache[$key] = null;
            }
        }
        else {
            $sql_result = $this->db->query(
                "SELECT `data`, `cache_key` FROM {$this->table}"
                . " WHERE `user_id` = ? AND `cache_key` = ?",
                $this->userid, $this->prefix.'.'.$key);

            if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                if (strlen($sql_arr['data']) > 0) {
                    $md5sum = md5($sql_arr['data']);
                    $data   = $this->unserialize($sql_arr['data']);
                }

                $this->db->reset();

                if ($nostore) {
                    return $data;
                }

                $this->cache[$key]      = $data;
                $this->cache_sums[$key] = $md5sum;
            }
            else {
                $this->cache[$key] = null;
            }
        }

        return $this->cache[$key];
    }