=> 2015-03-26 8:08 GMT+01:00 Tanel Poder <tanel@xxxxxxxxxxxxxx>: > Yep, sampling, especially infrequent sampling has its limitations. But the > problem is not really in V$SESSION itself (where ASH also gets its info > from internally), but how people *use* it. ASH regularly samples the > session state objects and even the infrequent short-running queries get > eventually caught in a sample, so when aggregating ASH data over minutes > and hours, the query will show up. > > V$SESSION tends to (often incorrectly) get used by just glancing at it > once and assuming that whatever showed up there at that particular point in > time must be what this problem session is stuck with. > <= > That was my point as well, sometimes DBAs do not use v$session correctly (for historical reasons probably, because before 10g most people had v$session_wait as mostly used and now they have all information joined in v$session ) A good experience for every DBA is to work at least once on some "near real time application" such as telecom front-office applications or stock exchange applications (and not only on classical ERP /inventory management applications) In those environnements you learn to think in terms of these short but frequently executed queries that easily bring the server up to 60-70% CPU (even more), while a quick look at v$session shows you only idle sessions. BTW, it's a pleasure for me to talk to Tanel Poder :-) Thanks Tanel for all the contribution you are giving to Oracle DBAs community. Dragutin