Better late than never :)

Relevant to today's outage.

-Chad

---------- Forwarded message ---------- From: Schubotz, Moritz schubotz@tu-berlin.de Date: Thu, Feb 6, 2014 at 2:04 PM Subject: FW: effects on caching To: "innocentkiller@gmail.com" innocentkiller@gmail.com

FYI

*From:* Schubotz, Moritz *Sent:* Mittwoch, 29. Januar 2014 14:33 *To:* wikitech-l@lists.wikimedia.org *Subject:* FW: effects on caching

Hi,

please be informed that recent changes in the Math extension and core might influence the stability of large MediaWiki instances due to a change in the cache key.

Please contact me for further details.

Best

Physikerwelt

*From:* Schubotz, Moritz *Sent:* Mittwoch, 29. Januar 2014 11:22 *To:* Antoine Musso *Subject:* effects on caching

Hi hashar,

I’d like to point out that the change that has been merged changes that caching behavior of MediaWiki for all pages that contain math.

The expected behavior can be described as follows:

“

By the way you can verfiy in the following way mediawiki/includes/parser/ParserCache.php ll 193 wfDebug( "ParserOutput cache found for key $parserOutputKey. \n" ); You see somehting like ParserOutput cache found for key wiki:pcache:idhash:1-0!0!*!*!*!*!*. for pages that contain math and ParserOutput cache found for key wiki:pcache:idhash:2-0!*!*!*!*!*!*. for pages that do not contain math

checkout https://gerrit.wikimedia.org/r/#/c/108490/

page without math still has the same key ParserOutput cache found for key wiki:pcache:idhash:2-0!*!*!*!*!*!*. but the key for the page with math the debug output will read [Math] New cache key: *!*!*!*!*!*!math=0 ParserOutput cache found for key wiki:pcache:idhash:1-0!*!*!*!*!*!*!math=0.

I think it's now save to merge since it won't affect pages that do not contain math and it won't have effects at all unless getMath is removed.

“

Now getMath was removed before the change to the math extension has been merged. If the changes are deployed in the same order as they were merged it will create errors visible for the visitors.

If they are merged in the correct order, all pages that contain math will be reRenderd on their first visit. (I think even by an anonymous user.) Since there is a high load I think that it means that all pages that contain math tags approx. 30 000 for the English Wikipedia will be rerenderd at the same time.

I expect that this will influence the performance of the the wmf system in a negative way, but I cannot decide how negative that will be.

Best

Physikerwelt