First reported by davosmith in https://github.com/remotelearner/moodle-mod_questionnaire/commit/9064a153f165a57e6b5fc5a6c86c626ec8a53a73#commitcomment-5970635

This runs out of memory on sites with a large number of questionnaires (e.g. 1.9 million records in this table).
A better approach would be to use 'get_recordset'.
(The line below will also need changing to:
$total = $DB->count_records('questionnaire_quest_choice');
)