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Performance: Refactor SQL that pins unread sticky posts to the top

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Ordering by `is_sticky and (unread subquery) desc` removes MySQL's
ability to use an index for ordering by `last_time`, which triggers a
filesort across the whole discussions table which is BAD.

This commit uses a union to add all stickied discussions to the query.
The results of the unioned queries are then ordered by the `is_sticky
and (unread subquery)` criteria, so the filesort only takes place on
a maximum of limit * 2 rows. Big performance win when you get up to
thousands of discussions!
This commit is contained in:
Toby Zerner 2017-11-12 21:28:17 +10:30
parent 7ff57e1ba4
commit 0ce00c6d16
1 changed files with 31 additions and 27 deletions
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58
extensions/sticky/src/Listener/PinStickiedDiscussionsToTop.php
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@ -25,7 +25,7 @@ class PinStickiedDiscussionsToTop
public function subscribe(Dispatcher $events)
{
$events->listen(ConfigureDiscussionGambits::class, [$this, 'addStickyGambit']);
$events->listen(ConfigureDiscussionSearch::class, [$this, 'reorderSearch']);
$events->listen(ConfigureDiscussionSearch::class, [$this, 'reorderSearch'], -100);
}
/**
@ -45,18 +45,15 @@ class PinStickiedDiscussionsToTop
$search = $event->search;
$query = $search->getQuery();
// TODO: ideally we might like to consider an event in core that is
// fired before the sort criteria is applied to the query (ie.
// immediately after gambits are applied) so that we can add the
// following order logic to the start without using array_unshift.
if (! is_array($query->orders)) {
$query->orders = [];
}
// If we are viewing a specific tag, then pin all stickied
// discussions to the top no matter what.
foreach ($search->getActiveGambits() as $gambit) {
$gambits = $search->getActiveGambits();
foreach ($gambits as $gambit) {
if ($gambit instanceof TagGambit) {
array_unshift($query->orders, ['column' => 'is_sticky', 'direction' => 'desc']);
@ -64,28 +61,35 @@ class PinStickiedDiscussionsToTop
}
}
// Otherwise, if we are viewing "all discussions" or similar, only
// pin stickied discussions to the top if they are unread. To do
// this we construct an order clause containing a subquery which
// determines whether or not the discussion is unread.
$subquery = $query->newQuery()
->selectRaw(1)
->from('users_discussions as sticky')
->whereRaw('sticky.discussion_id = discussions.id')
->where('sticky.user_id', '=', $search->getActor()->id)
->where(function ($query) {
$query->whereNull('sticky.read_number')
->orWhereRaw('discussions.last_post_number > sticky.read_number');
})
->where('discussions.last_time', '>', $search->getActor()->read_time ?: 0);
// Otherwise, if we are viewing "all discussions", only pin stickied
// discussions to the top if they are unread. To do this in a
// performant way we create another query which will select all
// stickied discussions, marry them into the main query, and then
// reorder the unread ones up to the top.
if (empty($gambits)) {
$sticky = clone $query;
$sticky->where('is_sticky', true);
$sticky->limit = $sticky->offset = $sticky->orders = null;
array_unshift($query->orders, [
'type' => 'raw',
'sql' => "(is_sticky and exists ({$subquery->toSql()})) desc"
]);
$query->union($sticky);
$orderBindings = $query->getRawBindings()['order'];
$query->setBindings(array_merge($subquery->getBindings(), $orderBindings), 'order');
$read = $query->newQuery()
->selectRaw(1)
->from('users_discussions as sticky')
->whereRaw('sticky.discussion_id = id')
->where('sticky.user_id', '=', $search->getActor()->id)
->whereRaw('sticky.read_number >= last_post_number');
// Add the bindings manually (rather than as the second
// argument in orderByRaw) for now due to a bug in Laravel which
// would add the bindings in the wrong order.
$query->orderByRaw('is_sticky and not exists ('.$read->toSql().') and last_time > ? desc')
->addBinding(array_merge($read->getBindings(), [$search->getActor()->read_time ?: 0]), 'union');
$query->unionOrders = array_merge($query->unionOrders, $query->orders);
$query->unionLimit = $query->limit;
$query->unionOffset = $query->offset;
}
}
}
}