DB time Less Than Elapsed Time - is there a performance problem? or is the report interval incorrect?

Hi All,
I've been given two awr reports for a 2 node, 11.1.0.7 RAC instance running on 
AIX and told to determine what the performance problem is with the system. 
Looking through the reports I can't say that I can see anything wrong with this 
system - at least based on the awrs I have been given (a few extracts from the 
reports given below). What I have noticed is that for both nodes the db time is 
considerably less than the elapsed time of the report - is this enough to 
deduce 
that this system is actually not busy and not performing any sort of work?.  
That said, the 'transactions per second' statistic is at 0.6 and 1.6 (for each 
node), additionally , logical reads, physical reads appear to be quite low.
Or perhaps one of the following possible:
(a) Since DB time excludes a few idle events - such as the sql*net related 
events that perhaps time is being spent there are not being recorded? Therefore 
db time is less than elapsed time and gives the illusion that the system is not 
busy?
(b) That perhaps the performance problem is short lived - lasts for a duration 
less than the elapsed time - therefore is not evident from these two awr reports
Thanks in advance for any pointers or help.

--Node1--:




Snap Id
Snap Time
Sessions
Cursors/Session
Begin Snap: 3479 17-Sep-10 08:59:58 67 2.6 
End Snap: 3480 17-Sep-10 10:00:10 76 2.1 
Elapsed:   60.19 (mins)     
DB Time:   8.54 (mins)     

Top 5 Timed Foreground Events 
Event
Waits
Time(s)
Avg wait (ms)
% DB time
Wait Class
DB CPU   434   84.72   
gc buffer busy acquire 956 5 5 0.98 Cluster 
gc cr block 2-way 7,515 4 1 0.74 Cluster 
IPC send completion sync 7,847 3 0 0.56 Other 
enq: PS - contention 4,534 2 1 0.49 Other 

Load Profile 


Per Second
Per Transaction
Per Exec
Per Call
DB Time(s): 0.1 0.2 0.01 0.01 
DB CPU(s): 0.1 0.2 0.00 0.01 
Redo size: 3,311.9 5,441.9     
Logical reads: 7,384.6 12,133.9     
Block changes: 154.9 254.5     
Physical reads: 0.2 0.3     
Physical writes: 1.4 2.3     
User calls: 11.3 18.6     
Parses: 17.7 29.2     
Hard parses: 0.1 0.2     
W/A MB processed: 1,211,497.8 1,990,648.6     
Logons: 0.9 1.4     
Executes: 26.5 43.5     
Rollbacks: 0.2 0.3     
Transactions: 0.6   
--End Node1--

--Node2--





Snap Id
Snap Time
Sessions
Cursors/Session
Begin Snap: 3479 17-Sep-10 09:00:29 61 2.5 
End Snap: 3480 17-Sep-10 10:00:41 59 1.8 
Elapsed:   60.19 (mins)     
DB Time:   15.60 (mins)     

Top 5 Timed Foreground Events 
Event
Waits
Time(s)
Avg wait (ms)
% DB time
Wait Class
DB CPU   738   78.83   
library cache load lock 714 38 53 4.03 Concurrency 
enq: TQ - DDL contention 509 24 47 2.58 Other 
db file sequential read 15,618 23 2 2.51 User I/O 
gc buffer busy acquire 1,206 6 5 0.64 Cluster 

Load Profile 


Per Second
Per Transaction
Per Exec
Per Call
DB Time(s): 0.3 0.2 0.00 0.02 
DB CPU(s): 0.2 0.1 0.00 0.02 
Redo size: 5,855.0 3,772.7     
Logical reads: 10,669.5 6,875.0     
Block changes: 907.2 584.6     
Physical reads: 6.3 4.1     
Physical writes: 2.1 1.4     
User calls: 12.7 8.2     
Parses: 41.3 26.6     
Hard parses: 0.2 0.1     
W/A MB processed: 1,327,061.6 855,097.2     
Logons: 1.0 0.6     
Executes: 65.3 42.1     
Rollbacks: 0.4 0.2     
Transactions: 1.6       

--End Node2--



      

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