jcrespo created this task.
jcrespo added projects: Wikidata, Wikibase.
Restricted Application added a subscriber: Aklapper.
TASK DESCRIPTION
This weekend, while an ongoing incident was being handled, I checked and saw
several badly performing queries running. These didn't have (I believe) any
relation with the incident, but any web request that takes more than 1 or a few
seconds (in the worse possible case) is worrying, as they can pile up and
create load issues on the database.
While there was several queries with bad performance (mostly related to
recentchanges and API), the worst occurring query right now is:
SELECT /* Wikibase\Lib\Store\Sql\SiteLinkTable::getLinks */ count(*) FROM
`wb_items_per_site` WHERE ips_site_id = '?';
where '?' can be any production wiki, but in particular, for enwiki, it
selects over **8 million rows**. We saw over 30 of those, over all s8 servers,
today Mar 8 at 8:18 UTC.
This not only takes over 1 minute to run, but is likely to be not useful
due to the amount of memory consumed.
While reading large number of rows can be useful for something like a
dump/analytics, it is unlikely to be useful for a web request. Moreso, the
application server will struggle to handle 2GB of data at a time, even in
memory, that this query returns.
Is it possible some extra WHERE or LIMIT was missing from the query?
TASK DETAIL
https://phabricator.wikimedia.org/T276762
EMAIL PREFERENCES
https://phabricator.wikimedia.org/settings/panel/emailpreferences/
To: jcrespo
Cc: Marostegui, hoo, Aklapper, jcrespo, maantietaja, Akuckartz, darthmon_wmde,
Nandana, Lahi, Gq86, GoranSMilovanovic, QZanden, LawExplorer, _jensen,
rosalieper, Scott_WUaS, abian, Wikidata-bugs, aude, Lydia_Pintscher, Mbch331
_______________________________________________
Wikidata-bugs mailing list
Wikidata-bugs@lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/wikidata-bugs
