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MDL-68647 forum: Improve the SQL performance in the privacy provider

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The idea here is to replace the existing LEFT JOINs and
OR / IS NOT NULL conditions with INNER JOINs and ANDs. So we gather the
discussions data from all three areas in individual queries, make their
UNION. The GROUP BY was present before and maybe it is not even needed
any more (due to how UNION works) but it should not hurt to keep it.

This leads to significantly improved performance.
This commit is contained in:
David Mudrák 2020-05-07 21:06:28 +02:00
parent 474e768a26
commit e2f1e10225
1 changed files with 34 additions and 25 deletions
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59
mod/forum/classes/privacy/provider.php
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@ -692,35 +692,44 @@ class provider implements
protected static function export_all_posts(int $userid, array $mappings) {
global $DB;
// Find all of the posts, and post subscriptions for this forum.
list($foruminsql, $forumparams) = $DB->get_in_or_equal(array_keys($mappings), SQL_PARAMS_NAMED);
$ratingsql = \core_rating\privacy\provider::get_sql_join('rat', 'mod_forum', 'post', 'p.id', $userid);
$sql = "SELECT
p.discussion AS id,
f.id AS forumid,
d.name,
d.groupid
FROM {forum} f
JOIN {forum_discussions} d ON d.forum = f.id
JOIN {forum_posts} p ON p.discussion = d.id
LEFT JOIN {forum_read} fr ON fr.postid = p.id AND fr.userid = :readuserid
{$ratingsql->join}
WHERE f.id ${foruminsql} AND
(
p.userid = :postuserid OR
p.privatereplyto = :privatereplyrecipient OR
fr.id IS NOT NULL OR
{$ratingsql->userwhere}
)
GROUP BY f.id, p.discussion, d.name, d.groupid
";
$commonsql = "SELECT p.discussion AS id, f.id AS forumid, d.name, d.groupid
FROM {forum} f
JOIN {forum_discussions} d ON d.forum = f.id
JOIN {forum_posts} p ON p.discussion = d.id";
// All discussions with posts authored by the user or containing private replies to the user.
list($foruminsql1, $forumparams1) = $DB->get_in_or_equal(array_keys($mappings), SQL_PARAMS_NAMED);
$sql1 = "{$commonsql}
WHERE f.id {$foruminsql1}
AND (p.userid = :postuserid OR p.privatereplyto = :privatereplyrecipient)";
// All discussions with the posts marked as read by the user.
list($foruminsql2, $forumparams2) = $DB->get_in_or_equal(array_keys($mappings), SQL_PARAMS_NAMED);
$sql2 = "{$commonsql}
JOIN {forum_read} fr ON fr.postid = p.id
WHERE f.id {$foruminsql2}
AND fr.userid = :readuserid";
// All discussions with ratings provided by the user.
list($foruminsql3, $forumparams3) = $DB->get_in_or_equal(array_keys($mappings), SQL_PARAMS_NAMED);
$ratingsql = \core_rating\privacy\provider::get_sql_join('rat', 'mod_forum', 'post', 'p.id', $userid, true);
$sql3 = "{$commonsql}
{$ratingsql->join}
WHERE f.id {$foruminsql3}
AND {$ratingsql->userwhere}";
$sql = "SELECT *
FROM ({$sql1} UNION {$sql2} UNION {$sql3}) united
GROUP BY id, forumid, name, groupid";
$params = [
'postuserid' => $userid,
'readuserid' => $userid,
'postuserid' => $userid,
'readuserid' => $userid,
'privatereplyrecipient' => $userid,
];
$params += $forumparams;
$params += $forumparams1;
$params += $forumparams2;
$params += $forumparams3;
$params += $ratingsql->params;
$discussions = $DB->get_records_sql($sql, $params);