CakePHP HAVING SUM Query superslow - where is room for improvement? - mysql

Question

This query kills the whole page (90% of the request time):
/**
* Checks if a conversation exists containing these users (at least two!)
* //TODO: fixme! SUPER-SLOW! 5s on a 6s page load total
*
* #param array $users Users to check on
* #param int $limit Limit - needs at least 2 users
* #return array Results
*/
public function partOfConversations($users, $limit = 5) {
$options = array(
'conditions' => array('ConversationUser.status <' => ConversationUser::STATUS_REMOVED),
'group' => array('ConversationUser.conversation_id HAVING SUM(CASE WHEN ConversationUser.`user_id` in (\'' . implode('\', \'', $users) . '\') THEN 1 ELSE 0 END) = ' . count($users) . ''),
'contain' => array('Conversation' => array('LastMessage')),
'limit' => $limit,
'order' => array('Conversation.last_message_id' => 'DESC')
);
return $this->ConversationUser->find('all', $options);
}
The resulting query is
SELECT `ConversationUser`.`id`, `ConversationUser`.`conversation_id`,
`ConversationUser`.`user_id`, `ConversationUser`.`status`, `ConversationUser`.`created`,
`Conversation`.`id`, `Conversation`.`user_id`, `Conversation`.`title`,
`Conversation`.`created`, `Conversation`.`last_message_id`, `Conversation`.`count`
FROM `comm_conversation_users` AS `ConversationUser`
LEFT JOIN `comm_conversations` AS `Conversation`
ON (`ConversationUser`.`conversation_id` = `Conversation`.`id`)
WHERE `ConversationUser`.`status` < 7 GROUP BY `ConversationUser`.`conversation_id`
HAVING SUM(CASE WHEN `ConversationUser`.`user_id` in
('2ed23d7c-dcc8-4d3b-8e7b-0fe018b0f9bf', '297e0fcc-8880-4bc7-9b57-0ba418b0f9bf')
THEN 1 ELSE 0 END) = 2
ORDER BY `Conversation`.`last_message_id` DESC
LIMIT 5
What it tries to do is to find out whether in a 1..x conversation two or more users are part of it (passed as $users).
Is there any way to speed that up?
Conversation 1:N ConversationUser N:1 User
Records are not too many: 70k Conversation, 130k ConversationUser
The fact that this also uses UUIds instead of normal AIID integers is probably making it worse.
But it should still not be 5s.

Answer 1

Besides ensuring your sql tables are optimized via indexes for that query, I think you should add another condition- only those records with acceptable user_id's.
Here is the appropriate WHERE clause
WHERE `ConversationUser`.`status` < 7
AND `ConversationUser`.`user_id` in
('2ed23d7c-dcc8-4d3b-8e7b-0fe018b0f9bf', '297e0fcc-8880-4bc7-9b57-0ba418b0f9bf')
Changing the PHP code to:
public function partOfConversations($users, $limit = 5) {
$options = array(
'conditions' => array('ConversationUser.status <' => ConversationUser::STATUS_REMOVED
,'ConversationUser.user_id' => $users),
'group' => array('ConversationUser.conversation_id HAVING SUM(CASE WHEN ConversationUser.`user_id` in (\'' . implode('\', \'', $users) . '\') THEN 1 ELSE 0 END) = ' . count($users) . ''),
'contain' => array('Conversation' => array('LastMessage')),
'limit' => $limit,
'order' => array('Conversation.last_message_id' => 'DESC')
);
return $this->ConversationUser->find('all', $options);
}