RE: Measuring PLSQL-SQL context switches

Others have referenced previous discussions and where the metric shows up.
I'm addressing when to care...

If you are executing a very expensive sql, it is not a big deal.

If you are executing a very cheap sql, then the context switch might well be
a significant proportion of the elapsed time and cost.

To assess the worst case overhead, grab one of those superfast versions of
select * from dual, measure the time of that query alone, slap it in place
of a PL/SQL block that loops on it the same number of times as in your real
PL/SQL program.

Subtract the number of iterations times the cost of select * from dual from
that execution, and that is the cost of the context switching.

(Okay, I'm leaving out the time to increment a loop counter, which is only a
big number in femtoseconds).

mwf
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Hemant K Chitale
Sent: Thursday, September 11, 2008 11:15 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Measuring PLSQL-SQL context switches


Is there a method to measure or estimate the impact of context 
switches when executing SQL inside a PLSQL block  -- particularly 
when the PLSQL block runs the same SQL statement very many times 
inside a loop ?

I can't seem to find a relevent statistic when I look at the list of 
statistics in the 10.2 Reference.

I know I could use timers to time the difference in execution time if 
I were to rewrite the PLSQL block but I would like to be able to 
measure and/or estimate the impact on execution time and/or CPU time 
given an existing piece of code .



Hemant K Chitale

http://hemantoracledba.blogspot.com



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