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List:       wikitech-l
Subject:    [Wikitech-l] Measuring the load-impact of query pages/maintenance reports
From:       "Federico Leva (Nemo)" <nemowiki () gmail ! com>
Date:       2012-11-29 22:39:52
Message-ID: 50B7E438.4010401 () gmail ! com
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Since a few years ago, we have several query [special] pages, also 
called "maintenance reports" in the list of special pages, which are 
never updated for performance reasons: 6 on all wikis and 6 more only on 
en.wiki. <https://bugzilla.wikimedia.org/show_bug.cgi?id=39667#c6>

A proposal is to run them again and quite liberally on all "small wikis" 
(to start with); another, to update them everywhere but one at a time 
and with proper breathing time for servers.[1]
The problem is, which pages are safe to run an update on even on 
en.wiki, and how frequently; and which would kill it? Or, at what point 
a wiki is too big to run such updates carelessly?[2]

Can someone estimate it by looking at the queries, or maybe by running 
them on some DB where it's not a problem to test?

We only know that originally pages were disabled if taking "more than 
about 15 minutes to update". If now such a page took, say, four times 
that ie 60 min, would it be a problem to update one such page per 
day/week/month? Etc.

Most updates seem to already rely on slave DBs, but maybe this should be 
confirmed; on the other hand, writing huge sets of results to DB 
shouldn't be a problem because those are limited as well.[3]

Nemo

[1] In (reviewed) puppet terms: <https://gerrit.wikimedia.org/r/#/c/33713/>
[2] Below that limit, a wiki should be "small" for 
<https://gerrit.wikimedia.org/r/#/c/33694> and frequently updated for 
the benefit of the editors' engagement.
[3] 'wgQueryCacheLimit' => array(
	'default' => 5000,
	'enwiki' => 1000, // safe to raise?
	'dewiki' => 2000, // safe to raise?
),

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