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MDL-51191 assign: Optimizing slow SQL query for MySQL

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This commit is contained in:
Jean-Philippe Gaudreau 2015-08-24 17:05:44 -04:00
parent f495510548
commit 286d6c81bf
1 changed files with 20 additions and 15 deletions
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35
mod/assign/db/upgrade.php
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@ -537,21 +537,26 @@ function xmldb_assign_upgrade($oldversion) {
FROM {assign_submission}
GROUP BY assignment, groupid, userid';
// Note: souterouter looks redundant below, but it forces
// MySQL to use an in memory table to store the results of the
// inner query. Without this MySQL would complain that the UPDATE
// is operating on the same table as the FROM (which is true).
$maxattemptidssql = 'SELECT souterouter.id FROM (
SELECT souter.id
FROM {assign_submission} souter
JOIN (' . $maxattemptsql . ') sinner
ON souter.assignment = sinner.assignment
AND souter.userid = sinner.userid
AND souter.groupid = sinner.groupid
AND souter.attemptnumber = sinner.maxattempt
) souterouter';
$select = 'id IN(' . $maxattemptidssql . ')';
$DB->set_field_select('assign_submission', 'latest', 1, $select);
$maxattemptidssql = 'SELECT souter.id
FROM {assign_submission} souter
JOIN (' . $maxattemptsql . ') sinner
ON souter.assignment = sinner.assignment
AND souter.userid = sinner.userid
AND souter.groupid = sinner.groupid
AND souter.attemptnumber = sinner.maxattempt';
// We need to avoid using "WHERE ... IN(SELECT ...)" clause with MySQL for performance reason.
// TODO MDL-29589 Remove this dbfamily exception when implemented.
if ($DB->get_dbfamily() === 'mysql') {
$params = array('latest' => 1);
$sql = 'UPDATE {assign_submission}
INNER JOIN (' . $maxattemptidssql . ') souterouter ON souterouter.id = {assign_submission}.id
SET latest = :latest';
$DB->execute($sql, $params);
} else {
$select = 'id IN(' . $maxattemptidssql . ')';
$DB->set_field_select('assign_submission', 'latest', 1, $select);
}
// Look for grade records with no submission record.
// This is when a teacher has marked a student before they submitted anything.