Database Reference
In-Depth Information
POOL BYTES
----------- ---------
shared pool 14680064
SQL> SELECT max(sample_time) - min(sample_time) AS interval
2 FROM v$active_session_history;
INTERVAL
-----------------------
+000000000 02:25:30.293
The data stored in active session history is externalized through the v$active_session_history view. Many
of the columns are equivalent to the ones of the v$session view (refer to the “Current Session Status” section for
information about them). As for the v$session view, the columns provided by the v$active_session_history view
strongly depend on the version you're using. For example, there are 50 in version 10.2.0.5 and 101 in version 12.1.0.1).
Compared to the v$session view, some of the columns are missing, some have slightly different content, and others
are available only in the v$active_session_history view. The most important columns that are available only in
the v$active_session_history view, or that have different contents, are the following (refer to the Oracle Database
Reference manual for additional information):
sample_id is an identifier associated to all samples taken by MMNL at a given time. Be aware
that it doesn't identify a single row in active session history.
sample_time is the timestamp at which MMNL takes the sample. Therefore, based on it, you
can reconstruct the activity performed by every session.
session_state expresses what the state of the session is. It's set to either WAITING or ON CPU .
If the session is waiting,
time_waited is the amount of time in microseconds that the session
spent waiting. In case one wait event occurrence spans two or more samples, the actual time
spent waiting is provided by the last sample and, for all other samples, time_waited is set
to 0. To illustrate, the output of the following query shows a session that waited for about
7.4 seconds for a lock:
SQL> SELECT sample_time, event, time_waited
2 FROM v$active_session_history
3 WHERE session_id = 137
4 ORDER BY sample_time;
SAMPLE_TIME EVENT TIME_WAITED
-------------------------- --------------------- -----------
...
27-APR-14 03.10.50.245 PM enq: TM - contention 0
27-APR-14 03.10.51.245 PM enq: TM - contention 0
27-APR-14 03.10.52.245 PM enq: TM - contention 0
27-APR-14 03.10.53.245 PM enq: TM - contention 0
27-APR-14 03.10.54.245 PM enq: TM - contention 0
27-APR-14 03.10.55.245 PM enq: TM - contention 0
27-APR-14 03.10.56.245 PM enq: TM - contention 0
27-APR-14 03.10.57.245 PM enq: TM - contention 7390676
...
 
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