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MDL-77965 quiz: Improve efficiency of the data export

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Before this change the query used an index scan to perform the
export, this could be really expensive on the database.

After the change the the query will use far more efficient joins,
on a large MySQL instance this can take minutes off of the query
time.

In additon the query was returning two columns that are not used
in the function. The layout column was causing the UNION to fail
on Oracle as it cannot compare text columns, removing these
columns from the returned data should further increase
performance further.
This commit is contained in:
Neill Magill 2023-04-24 10:48:17 +01:00
parent 32a915ecd2
commit 79150cf9bb
1 changed files with 43 additions and 14 deletions
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57
mod/quiz/classes/privacy/provider.php
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@ -480,31 +480,60 @@ class provider implements
$userid = $contextlist->get_user()->id;
list($contextsql, $contextparams) = $DB->get_in_or_equal($contextlist->get_contextids(), SQL_PARAMS_NAMED);
$qubaid = \core_question\privacy\provider::get_related_question_usages_for_user('rel', 'mod_quiz', 'qa.uniqueid', $userid);
$qubaid1 = \core_question\privacy\provider::get_related_question_usages_for_user(
'rel1',
'mod_quiz',
'qa.uniqueid',
$userid
);
$qubaid2 = \core_question\privacy\provider::get_related_question_usages_for_user(
'rel2',
'mod_quiz',
'qa.uniqueid',
$userid
);
// The layout column causes the union in the following query to fail on Oracle, it also appears to not be used.
// So we can filter the return values to be only those used to generate the data, this will have the benefit
// improving performance on all databases as we will no longer be returning a text field for each row.
$attemptfields = 'qa.id, qa.quiz, qa.userid, qa.attempt, qa.uniqueid, qa.preview, qa.state, qa.timestart, ' .
'qa.timefinish, qa.timemodified, qa.timemodifiedoffline, qa.timecheckstate, qa.sumgrades, ' .
'qa.gradednotificationsenttime';
$sql = "SELECT
c.id AS contextid,
cm.id AS cmid,
qa.*
$attemptfields
FROM {context} c
JOIN {course_modules} cm ON cm.id = c.instanceid AND c.contextlevel = :contextlevel
JOIN {course_modules} cm ON cm.id = c.instanceid AND c.contextlevel = :contextlevel1
JOIN {modules} m ON m.id = cm.module AND m.name = 'quiz'
JOIN {quiz} q ON q.id = cm.instance
JOIN {quiz_attempts} qa ON qa.quiz = q.id
" . $qubaid->from. "
WHERE (
qa.userid = :qauserid OR
" . $qubaid->where() . "
) AND qa.preview = 0
" . $qubaid1->from. "
WHERE qa.userid = :qauserid AND qa.preview = 0
UNION
SELECT
c.id AS contextid,
cm.id AS cmid,
$attemptfields
FROM {context} c
JOIN {course_modules} cm ON cm.id = c.instanceid AND c.contextlevel = :contextlevel2
JOIN {modules} m ON m.id = cm.module AND m.name = 'quiz'
JOIN {quiz} q ON q.id = cm.instance
JOIN {quiz_attempts} qa ON qa.quiz = q.id
" . $qubaid2->from. "
WHERE " . $qubaid2->where() . " AND qa.preview = 0
";
$params = array_merge(
[
'contextlevel' => CONTEXT_MODULE,
'qauserid' => $userid,
],
$qubaid->from_where_params()
);
[
'contextlevel1' => CONTEXT_MODULE,
'contextlevel2' => CONTEXT_MODULE,
'qauserid' => $userid,
],
$qubaid1->from_where_params(),
$qubaid2->from_where_params(),
);
$attempts = $DB->get_recordset_sql($sql, $params);
foreach ($attempts as $attempt) {