I'm guessing MySQL doesn't support this (hence the need for a cron job), but postgres lets you set a statement_timeout on the connection. It will force kill queries that go beyond that timeout. I worked on an app not too long enough that occasionally would have some queries go off the rails and start blocking everything. We set up postgres to just kill off anything taking 30s automatically, and then were able to root out the issues without worrying about everything blocking on these broken queries and taking down our systems.