Three identical queries from the 'research_prod' user have just passed one month execution time on s1-anlytics-slave:

select count(*)
from staging.ourvision r
where exists (
  select *
  from staging.ourvision r1
          inner join
       staging.ourvision r2    
          on r2.sha1 = r1.sha1
    where r1.page_id = r.page_id
      and r2.page_id = r.page_id
      and DATE_ADD(r.timestamp, INTERVAL 1 HOUR)
      and r2.timestamp between r.timestamp and DATE_SUB(r.timestamp , INTERVAL 1 HOUR)
      and  r1.sha1!= r.sha1
);

I havn't checked to see if the queries are just that amazingly slow, or if they're part of a larger ongoing transaction. In any case, three month-long transactions is pushing the resource limits of the slave and will soon result in either mass replication lag or some other interesting lockup that may in turn take days to rollback :-)