> I recently turned on TIMED_STATISTICS to help me with tuning the
> database. In particular, I'm looking at the number of recursive calls
> and the CPU time they use in V$SYSSTAT. The manuals frequently point
> out that gathering timed statistics implies extra performance
> overhead. This got me wondering: do these statistics include that
> overhead? If so, is there any way to determine to what extent they are
All that TIMED_STATISTICS does is get the system time before and after
events. While this may sound like a lot its only a few instructions on
a machine capable of millions of instructions per second. I know, it
all adds up.
I remember several years ago that a knowledgeable Oracle internals
expert (few that there were back then) actually said that turning on
TIMED_STATISTICS under VMS actually improved performance as it avoided
some privilege level changes for the process (VMS code privilege
This was also discussed on oracle-l quite a while ago and I vaguely
remember someone having done load tests at their site and could not
identify any slowdown or overhead. Their site was a fairly small VAX so
the overhead would have been visible.
Turning on SQL_TRACE is a totally different load situation.
T T T T T T T T Bruce Pihlamae
I I I I I I I I National Library of Australia
T T T T T T T T Phone: +616 262-1575
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"If you swallow a live frog first thing in the morning;
nothing worse will happen to either of you that day."