https://bugzilla.wikimedia.org/show_bug.cgi?id=54195

Faidon Liambotis <[email protected]> changed:

           What    |Removed                     |Added
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           Priority|High                        |Highest
                 CC|                            |[email protected],
                   |                            |[email protected]

--- Comment #20 from Faidon Liambotis <[email protected]> ---
OK, I had another quick look, as this in combination with consistent hashing
directing /wiki/Special:CentralAutoLogin/start?type=script to a single Varnish
backend produced a partial outage by exhausting its resources. (this has been
workarounded since with https://gerrit.wikimedia.org/r/#/c/95458/ )

This is far more than just "caching". I'm going to report these here so we
don't get lost into multiple bugs, but feel free to fork into other bugs as
needed:

1) From Varnish text frontends, i.e. *all* text client-side requests (hits &
misses), the top 10 URLs are:
  6895.39 RxURL          /wiki/Special:CentralAutoLogin/start?type=script
  5627.74 RxURL         
/w/index.php?title=MediaWiki:Wikiminiatlas.js&action=raw&ctype=text/javascript&smaxage=21600&maxage=86400
  3235.81 RxURL         
/wiki/Special:CentralAutoLogin/createSession?gu_id=0&type=script&proto=https
  2137.83 RxURL         
/wiki/Special:CentralAutoLogin/createSession?gu_id=0&type=script&proto=http
  1981.98 RxURL         
/w/index.php?title=MediaWiki:EnhancedCollapsibleElements.js&action=raw&ctype=text/javascript
  1943.81 RxURL         
/w/index.php?title=MediaWiki:Common.js/NormalizeCharWidth.js&action=raw&ctype=text/javascript
  1567.70 RxURL         
/wiki/Special:CentralAutoLogin/checkLoggedIn?wikiid=enwiki&proto=https&type=script
  1383.12 RxURL          /favicon.ico
  1266.87 RxURL         
/w/index.php?title=%E7%89%B9%E5%88%A5:%E4%B8%AD%E5%A4%AE%E7%AE%A1%E7%90%86%E8%87%AA%E5%8B%95%E3%83%AD%E3%82%B0%E3%82%A4%E3%83%B3/star
  1020.66 RxURL         
/w/index.php?title=MediaWiki:OSM.js&action=raw&ctype=text/javascript&smaxage=21600&maxage=86400

(also note how the first is double the requests from the third and triple the
requests from fourth)

and from the top-50 URLs, 10 (20%) are CentralAutoLogin URLs, namely:
  6944.76 RxURL          /wiki/Special:CentralAutoLogin/start?type=script
  3003.28 RxURL         
/wiki/Special:CentralAutoLogin/createSession?gu_id=0&type=script&proto=https
  2273.40 RxURL         
/wiki/Special:CentralAutoLogin/createSession?gu_id=0&type=script&proto=http
  1452.62 RxURL         
/wiki/Special:CentralAutoLogin/checkLoggedIn?wikiid=enwiki&proto=https&type=script
   551.49 RxURL         
/wiki/Special:CentralAutoLogin/checkLoggedIn?wikiid=jawiki&proto=https&type=script
   362.93 RxURL         
/wiki/Special:CentralAutoLogin/checkLoggedIn?wikiid=eswiki&proto=https&type=script
   298.33 RxURL         
/wiki/Special:CentralAutoLogin/checkLoggedIn?wikiid=zhwiki&proto=http&type=script
   293.00 RxURL         
/wiki/Special:CentralAutoLogin/checkLoggedIn?wikiid=enwiki&proto=http&type=script
   289.84 RxURL         
/wiki/Special:CentralAutoLogin/createSession?gu_id=0&type=1x1&proto=https
   240.99 RxURL         
/wiki/Special:CentralAutoLogin/checkLoggedIn?wikiid=ptwiki&proto=https&type=script

Moreover, these stats do not include the localized URLs that I'm seeing, such
as
http://de.wikipedia.org/w/index.php?title=Spezial:Zentrale_automatische_Anmeldung/start&type=script
(localized URLs for such basic functions are a bad idea, as it doesn't help us
aggregate URLs counts and find outliers like the above)

And, surpisingly, does not include the 1x1 URL that I see e.g. on all(?) enwiki
pages as:
<noscript><img
src="//en.wikipedia.org/w/index.php?title=Special:CentralAutoLogin/start&amp;type=1x1"
alt="" title="" width="1" height="1" style="border: none; position: absolute;"
/></noscript></div>
which also comes with Cache-control: private.

The fact that these URLs are so popular points to far more than just editors
attempting to login -- it surely includes anonymous page views and it's
probably aggravated by the fact that due to caching headers, we do not make use
of client-side caching. I see ext.centralauth.centralautologin.js doing such
requests and that script being loaded on every anon, but it's clearly not my
area of expertise.

Those URLs not being cached also means these get passed through to appservers
and increasing their load significantly, which the original point of this
report. It's also very apparent now, though, that they're causing problems in
all kinds of layers in our infrastructure (Varnish frontend/backend hit ratio
is down the drain, Varnish backends were/are suffering) and possibly causing a
client-side slow-down.

I think we can fix the caching issues -even for redirects depending on GeoIP-
but first and foremost we need to stop forcing all page views to requests all
kinds of (uncacheable) CentralAutoLogin URLs in this way.

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