MySQL CPU pegged on specific query Very similar (almost exact) to this question: Poor performance on midsized site / Queries without index?

CPU keeps getting pegged to 100% for MySQL, which makes the admin interface very slow (the site is cached using fastCGI, so generally the site still performs well regardless).

The troublesome query:

FROM (SELECT `elements`.`id` AS `elementsId`, `entries`.`sectionId`, `entries`.`typeId`, `entries`.`authorId`, `entries`.`postDate`, `entries`.`expiryDate`
FROM `elements` `elements`
JOIN `elements_i18n` `elements_i18n` ON elements_i18n.elementId = elements.id
JOIN `content` `content` ON content.elementId = elements.id
LEFT JOIN `relations` `sources1` ON (sources1.targetId = elements.id)
LEFT JOIN `relations` `targets1` ON (targets1.sourceId = elements.id)
JOIN `entries` `entries` ON entries.id = elements.id
JOIN `sections` `sections` ON sections.id = entries.sectionId
LEFT JOIN `structures` `structures` ON structures.id = sections.structureId
LEFT JOIN `structureelements` `structureelements` ON (structureelements.structureId = structures.id) AND (structureelements.elementId = entries.id)
WHERE (((((elements_i18n.locale = 'en_us') AND (content.locale = 'en_us')) AND (elements.archived = 0)) AND ((elements.enabled = 1) AND (elements_i18n.enabled = 1) AND (entries.postDate &lt;= '2017-12-29 15:41:28') AND ((entries.expiryDate is null) OR (entries.expiryDate &gt; '2017-12-29 15:41:28')))) AND (elements_i18n.enabled = 1)) AND ((sources1.sourceId='52') OR (targets1.targetId='52'))
GROUP BY `elements`.`id`) derivedElementsTable


What are CPU has looked like:



I'm not sure where I should start hunting this down. This appears to only happen for the en_us locale, I haven't recorded another locale showing this. This is on a staging site on Digital Ocean, so it's getting zero traffic. It's also being managed by Forge on PHP 7.1.

Could I get any advice for hunting down the php that might be leading to this? It's not happening as a result of any clear action.
I wouldn't be too worried about MySQL using 100% CPU, especially on a multi-core VPS. But a good way to track down things like this is to enable the MySQL slow query log

You can set whatever thresholds you want, and then peruse the log at your convenience to see the queries that are actually slowing things down.