Different response times for same SQL statement in Oracle - database-performance

Question

I am running a simple select statement in my database (connected from a remote machine using putty). I connected to SQLPLUS from the putty and executing the select statement. But getting different response times each time I run the query. Here are my observations.
1) Enabled the trace(10046). "elapsed_time" in the trace file is different for each execution of the query.
2) there is a huge difference in the elapsed time which is displayed on the console, and which is there in trace file... From the Putty, the elapsed time is showing approx. 2-3 secs. Whereas the elapsed time logged in the trace is showing the elapsed time as 1 sec... What is the difference between elapsed time on the putty console and trace file log?
Putty Console output:
select * from WWSH_TEST.T01DATA_LINK
489043 rows selected.
Elapsed: 00:02:57.16
Tracefile output:
select *
from
WWSH_TEST.T01DATA_LINK
call count cpu elapsed disk query current rows
---- ------- ------- --------- -------- -------- ------- ------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 32604 0.38 2.32 10706 42576 0 489043
From the putty console, the elapsed time is showing as 2.57 secs, whereas from the trace file the elapsed time is 2.32 .. Why we see this difference?
Moreover, when I am running this same SQL statement repeatedly, I could see different elapsed times in the trace files (ranging from 2.3 to 2.5 secs) .. What could be the reason for this difference in response time when there is no change in the database at all.
Database Version: 11.2.0.3.0

Answer 1

It looks like the time difference is the "client processing" - basically the time spent by sqlplus formatting the output.
Also, it looks like your array size is 15. Try running with a larger array size, such as 512 or 1024.
The mechanism to set the array size will vary from client to client. In sqlplus:
set arraysize 1024
The fetch time does not include network time, but if you use a level 8 trace
alter session set events '10046 trace name context forever, level 8';
this will given you wait events. The one to look for is SQL*Net message from client, which is basically the time the database is waiting to be asked to do something, such as fetch the next set of rows.