Database Reference
In-Depth Information
The report continues by providing information about the period of time it covers (beginning, end, and duration),
the number of sessions at the beginning and at the end of the period, as well as, from version 11.1 onward, the DB
time (106.55) and the CPU utilization (28.35). In this part, you should carefully check that the report covers the
period of time you have to analyze. Note that the average number of active sessions (7.1), which is available as of
version 11.1.0.7 only, is computed by dividing the DB time by the elapsed time:
Snapshot Snap Id Snap Time Sessions Curs/Sess Comment
~~~~~~~~ ---------- ------------------ -------- --------- ------------------
Begin Snap: 548 23-Apr-14 18:30:40 57 1.6
End Snap: 549 23-Apr-14 18:45:40 59 1.5
Elapsed: 15.00 (mins) Av Act Sess:
7.1
DB time:
106.55
(mins) DB CPU:
28.35
(mins)
The report goes on to provide the size of the most important SGA components. Be aware that if either the buffer
cache or the shared pool were resized during the observed period, the value at the end of the period would be shown.
Otherwise, as in the following example, only the value at the beginning of the period is shown:
Cache Sizes Begin End
~~~~~~~~~~~ ---------- ----------
Buffer Cache: 728M Std Block Size: 8K
Shared Pool: 260M Log Buffer: 7,992K
Next, you see plenty of metrics about the processing performed per second, per transaction, and, for a couple of
metrics, per execution and per call:
Load Profile Per Second Per Transaction Per Exec Per Call
~~~~~~~~~~~~ ------------------ ----------------- ----------- -----------
DB time(s):
7.1
0.0 0.01 0.00
DB CPU(s):
1.9
0.0 0.00 0.00
Redo size: 392,163.4 1,928.3
Logical reads: 406,805.1 2,000.3
Block changes: 2,822.9 13.9
Physical reads: 579.7 2.9
Physical writes: 377.8 1.9
User calls: 2,895.2 14.2
Parses: 0.6 0.0
Hard parses: 0.0 0.0
W/A MB processed: 0.1 0.0
Logons: 0.0 0.0
Executes: 1,364.1
6.7
Rollbacks: 0.0 0.0
Transactions:
203.4
Most of the previous metrics can't be used directly to assess whether the database instance was experiencing
a performance problem. Their main purpose is twofold. First, they give you a general feeling about the load. For
example, in the previous case, we see that there are 203.4 transactions per second and that each of them, on average,
carries out 6.7 executions. So, you know that the system is for sure doing some processing. Second, they help
