On 8i there are several cursor sharing bugs (1210242,
918002, and others) where cursors aren't shared when
timed_statistics is enabled. Most of them have been
fixed in 8.1.6.3 and 8.1.7.1. A workaround for most
of them is to set _SQL_EXEC_PROGRESSION_COST=0.
Symptoms are contention on the shared pool and library
cache latches; high version_count values in v$sqlarea.
Other than these bugs the impact is minimal, as Don
and others have mentioned, and the benefits far
outweigh the costs.
HTH,
- Anita
- Don Granaman <granaman_at_home.com> wrote:
> 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"
> <ORACLE-L_at_fatcity.com>
> 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
> > INET: greg.solomon_at_betfair.com
> >
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Received on Wed Jun 20 2001 - 11:35:05 CDT
