See https://lists.wikimedia.org/pipermail/glamtools/2015-September/000520.html
Dear all, Is there an admin among you who can kill my present GWT-job? * Most files to be uploaded are not present in the source database * Latest 2 files uploaded had unexplainable.. wrong metadata (speedy deletion requested), so this looks bad for further upcoming files. I am a bit ashamed to have to ask this... Compare https://commons.wikimedia.org/w/index.php?title=Special:Log&limit=500&type=gwtoolset&user=Hansmuller Thank you very much, https://commons.wikimedia.org/wiki/User:Hansmuller
Gwtoolset has no built in cancel support, so the only way to cancel a job, is to actually remove things from the job queue. Note that other users are currently using gwtoolset too, so we don't want to cancel their jobs.
Last time jobs were deleted from gwtoolset was around Jan 22 (see https://phabricator.wikimedia.org/T87040#984282 ). @Krenair and @Tgr I think know details