Script to explore the memory usage of Moodle's database driver

dbmemtest.php

<?php

require_once(__DIR__ . '/config.php');
raise_memory_limit(MEMORY_HUGE);

$method = 'get_records'; // One of the cases from the switch below.
$numrows = 512 * 1024;
$generatorquery = "
        SELECT i AS id, 'A thirty-two char string' || lpad('' || i, 8) AS name
          FROM generate_series(1, $numrows) i";

switch ($method) {
    case 'none':
        $data = [];
        break;

    case 'array_fill_object':
        $data = [];
        for ($i = 0; $i < $numrows; $i++) {
            $data[] = (object) ['id' => "$i", 'name' => 'A thirty-two char string' . str_pad($i, 8, STR_PAD_LEFT)];
        }
        break;

    case 'array_fill_object_other':
        $data = [];
        for ($i = 0; $i < $numrows; $i++) {
            $row = new stdClass();
            $row->id = "$i";
            $row->name = sprintf('A thirty-two char string% 8d', $i);
            $data[] = $row;
        }
        break;

    case 'get_records':
        $data = $DB->get_records_sql($generatorquery);
        break;

    case 'get_recordset':
        $rs = $DB->get_recordset_sql($generatorquery);
        $data = [];
        foreach($rs as $row) {
            $data[] = $row;
        }
        $rs->close();
        break;
}

//var_dump($data);
$PAGE->set_context(context_system::instance());
$PAGE->set_url('/dbmemtest.php');
$PAGE->set_title('DB memory usage test');

echo $OUTPUT->header();
echo $OUTPUT->heading($method);
echo count($data);

echo $OUTPUT->footer();

// method              RAM (MB)      RAM peak (MB)
// none                      39            40.2
// array_fill_object        321           322.1
// array_fill_object_other  449           450.1
// get_records              369           554
// get_recordset            352.8         354