I set small queue to allow only 1 concurrent query:
alter system set `exec.queue.enable`=TRUE;
alter system set `exec.queue.small`=1;
When running 2 small queries, one of them is pending which is expected.
(See pic 1)
After about 5mins(exec.queue.timeout_millis), the pending SQL starts. now we have 2 queries running in small queue.
(See pic 2)