function rebuildDB()
    {
        $depdb = array('_version' => $this->_version);
        if (!$this->hasWriteAccess()) {
            // allow startup for read-only with older Registry
            return $depdb;
        }

        $packages = $this->_registry->listAllPackages();
        if (PEAR::isError($packages)) {
            return $packages;
        }

        foreach ($packages as $channel => $ps) {
            foreach ($ps as $package) {
                $package = $this->_registry->getPackage($package, $channel);
                if (PEAR::isError($package)) {
                    return $package;
                }
                $this->_setPackageDeps($depdb, $package);
            }
        }

        $error = $this->_writeDepDB($depdb);
        if (PEAR::isError($error)) {
            return $error;
        }

        $this->_cache = $depdb;
        return true;
    }