I have the following script which is preparing user data for output:

// this first line simply read the data from the file into an array.
// memory usage at this point: 13.5830 MB
    if ($val = baw_data($BAW_CURR['site_name'], "VISITOR", $BAW_CURR['yearmonth'])) {
        // I want to summarize people which have a hit/page ratio <1 into the user 'script'
        // so I prepare the array for it.
        $val['script'] = array('script',0,0,0,0,'');
        // now I iterate the data.
        foreach ($val as $dns => $data) {
            // this next line gives me a debug-output and tells me the memory usage & time spent.

            baw_debug($dns . "start", false, true);
            $ratio = 0;
            if ($data[0] > 0) {
                $ratio = baw_num_format($data[1] / $data[0], 2);
            }
            if ($ratio <= 1) {
                $latest_date_bots = max($data[3], $latest_date_bots);
                $val['script'] = array(
                    $BAW_MES['assumedscript'],
                    $val['script'][0] + $data[0],
                    $val['script'][1] + $data[1],
                    $val['script'][2] + $data[2],
                    baw_num_format(($val['script'][0] + $data[0]) / ($val['script'][1] + $data[1]),2),
                    $latest_date_bots
                );
                unset($val[$dns]);
            } else {
                $val[$dns] = array($dns,$data[0],$data[1],$data[2],$ratio,$data[3]);
            }
            baw_debug($dns . "end", false, true);
        }
    }