Why is time_waited more than total elapsed time ?

I am wondering why my time_waited on 'db file sequential read' is MUCH more than my total elapsed time in tkprof.

I ran a long query in a controlled test enrivornment ( no other session running) and the query was executed right after a fresh bounce

Here is the tkprof result of it:

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------

Parse        1      0.04       0.09          1         18          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch     5807     21.94     296.24      76109     376395         37       87091


------- ------  -------- ---------- ---------- ---------- ----------  ----------

total     5809     21.98     296.33      76110     376413         37       87091

Note here that my elased time is 296.33 seconds.

At the same time, I also trapped the difference of v$system_event before and after the run, and here is the result:

TIMESTAMP           EVENT                               TOTAL_WAITS TIME_WAITED


------------------- ----------------------------------- ----------- -----------

2002/06/20 10:02:44 db file sequential read                   80962       41924
2002/06/20 10:02:44 db file scattered read                      291        1264

Note here that my sequential read is 419.24 seconds.

There are nothing else running and this is only a single session query. My parallel_min_servers is set to 0 and there is no hint in this query to tell Oracle to use parallel query.

I thought the elased time (roughtly) = CPU time + event wait time. But this completely confuses me. Can anyone please explain this ?

Thanks in advance.

-bass

BTW, the reason I trap the diff before and after on v$system_event, instead of using v$session_event, is the latter showed all zero, so the data is useless - maybe another question for those who know why. Received on Thu Jun 20 2002 - 12:32:15 CDT