Jul 30 2019
Long queries happened only in the recent months, probably related to https://phabricator.wikimedia.org/T226050 and the revision table changes.
I have disabled comment join for several wikis which where slower : enwiki, commonswiki, wikidatawiki, viwiki, itwiki, cywiki, arwiki, ruwiki, eswiki, ukwiki, plwiktionary. This mean no more revert detection for users on those wikis.
Jul 29 2019
Wikiscan needs to refresh recent stats every 30 minutes (ideally) for each wiki. It also need to refresh old stats periodically, a process which can take several days per wikis, and also other data like user groups.
All of this for 380 wikis and probably 800 wikis in the coming month. Also any visitor looking at contributions/blocks for ip ranges needs a connection.
Wikiscan use several workers to update all wikis https://wikiscan.org/?menu=allsites&submenu=workers, actual needs are between 5-12 connections. I plan to extend wikis from 380 wikis to more than 800 (https://meta.wikimedia.org/wiki/Grants:Project/Rapid/Akeron/Wikiscan), so I think 15 connections could be required at peaks (some of them are only needed few seconds).
There is also a secondary usage to display contributions and block logs for ip ranges like https://fr.wikiscan.org/plage-ip/220.127.116.11/16?submenu=edits, it depends on visiting users and web crawlers.
Jul 8 2019
Hi, yes it is used to access Wikimedia SQL replicas.