When you have timed statistics on all your doing is when oracle acquires a
resource it stores the time, then it is done, it stores a time. This is
very low resource task, even compared to many of the smallest transactions.
Most transactions outweigh the time to do this by 100 - 1000 fold or more.
Considering wait events are so much more effective and useful for tuning
than ratio, proper performance is almost impossible to obtain without using
time statistics. Another thing to note is when you tune a database, it
doesn't stay properly tuned forever. Without statistics it is hard to see
when other problems start to crop up until it is too late. I.E., if your
log parrallel write time increases because of increased redo generation and
lack of enough spindles cannot be noticed in due time without proper
statistics.
"Walking on water and developing software from a specification are easy if
both are frozen."
Christopher R. Spence
Oracle DBA
Fuelspot
-----Original Message-----
Sent: Wednesday, June 20, 2001 12:31 PM
To: Multiple recipients of list ORACLE-L
Timed statistics has very little performance impact - most of the work is
already done internally anyway. It is very useful - for tkprof, wait
statistics, and a few other things. I always set it and have for years -
even on exceptionally hot OLTP systems. A guy I know from the Oracle Center
of Expertise gave a talk to our local user group two weeks ago and mentioned
that he had never seen any noticeable performance degradation due to setting
it. If there is any significant performance impact, you have much bigger
problems than timed statistics.
I have seen only one very specific bug related to setting it. That was just
recently after upgrading an 8.1.7.0.0 OPS database on Sun Solaris to
8.1.7.1.0. Prior to the upgrade, no problem. After the upgrade, shutting
down an instance while in parallel mode resulted in a long wait (several
additional minutes, even with immediate) and an ORA-07445 error that
generated a trace file and a cdump. The problem is that one of the OPS
processes, bsp, would not shut down cleanly. This is one of the last things
that happens during the instance shutdown. Since the database had already
been dismounted, it probably isn't that serious. As far as I know, it only
happens with PARALLEL_SERVER=TRUE in 8.1.7.1.0 (on Sun Solaris at least) and
it did not happen in any prior release/patchlevel of 8i.
-Don Granaman
[certifiable OraSaurus]
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>
Sent: Wednesday, June 20, 2001 10:16 AM
> Hi
>
> Has anyone experienced any problems after setting timed_statistics to true
> on a prod database (at system level) ?
>
> Can anyone give me a guess as to the performance hit of doing this ?
>
> Running Oracle 8.1.6, there are fairly predictable periods of high,
medium,
> and low load so I can avoid collecting stats at peak periods if necessary.
>
> Cheers
> Greg
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> Author: Greg Solomon
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