Currently, WDQS's timeout prevents many legitimate queries involving large datasets (e.g. various counting queries tied to large wikis, see example at bottom). The performance and attack issues are understood.
This ticket requests that in addition to the anonymous public service, there would be an OAuth-dependent service for logged in users, that would permit users with a "trusted query runner" bit (see below) to run queries with a significantly longer -- perhaps 5 minutes? -- timeout.
The bit could be defined and managed by the Wikidata community. That community could either come up with criteria for giving out the bit, or just empower Wikidata admins to give out the bit at their discretion.
Obviously, Ops and Search must retain responsibility for the cluster's health, so would be empowered to remove the "trusted query runner" bit if a user is seen to be abusing or attacking the servers.
Example query that times out on larger wikis:
I can run this query -- which really impresses people, like an instant x-ray of a Wikipedia's coverage of people -- for smaller languages, but not for, say, nl, de, fr, zh, ru, en.