I think you're right, the segment queries are definitely running on an Actor's spawn thread.    https://github.com/pentaho/mondrian/blob/master/mondrian/src/main/java/mondrian/rolap/SqlStatement.java#L314-L315    Also, when a cancelation comes in, it'll come from yet another thread (the user thread, or RolapResultShepherd) so that's another possible concurrent issue.    https://github.com/pentaho/mondrian/blob/master/mondrian/src/main/java/mondrian/rolap/RolapResultShepherd.java#L84