Re: System stats

I agree with Mladen here. It's incredibly annoying that Oracle's official stance is to leave the vales at the default now.

That just tells me that Oracle Corp has lost focus on how the optimizer should perform and has become unwieldy.

Mathematically, it makes sense to always gather system stats to aid the optimizer (where always is do it once during load).

The fact they're saying don't do that is a clear indicator of a problem in the design/implementation of the calculations.

Just my $0.015

Chris

On Mon, Mar 25, 2019, 8:11 PM Mladen Gogala <gogala.mladen_at_gmail.com> wrote:

> System statistics is calibration. I measures your CPU speed and your IO
> speed. That's it. Generally speaking, your performance can benefit greatly
> from the information about the particular system it is running. There is no
> need to re-run it, unless there is a change in your environment: new
> motherboard, new memory, new storage or new PHB. Here is the data that is
> collected when system statistics is gathered:
>
> SQL> select * from aux_stats$;
> SNAME PNAME PVAL1 PVAL2
> SYSSTATS_INFO STATUS COMPLETED
> SYSSTATS_INFO DSTART 03-25-2019 19:40
> SYSSTATS_INFO DSTOP 03-25-2019 19:45
> SYSSTATS_INFO FLAGS 1
> SYSSTATS_MAIN CPUSPEEDNW 3254.90196078431
> SYSSTATS_MAIN IOSEEKTIM 10
> SYSSTATS_MAIN IOTFRSPEED 4096
> SYSSTATS_MAIN SREADTIM 16.012
> SYSSTATS_MAIN MREADTIM 29.361
> SYSSTATS_MAIN CPUSPEED 4061
> SYSSTATS_MAIN MBRC 11
> SYSSTATS_MAIN MAXTHR 86223872
> SYSSTATS_MAIN SLAVETHR 206848
>
>
> 13 rows selected.
>
> As you can see, it describes your system: CPU speed, IO seek time and
> transfer speed, single block read time, multiple blocks read time and the
> measured optimal value for multi-block read count. Jonathan Lewis has
> written quite a few very instructive articles about particular values in
> this table.
>
> Having said that, it is completely ridiculous to measure system statistics
> without any activity. You want the values which would correspond to your
> typical workload and that cannot be measured on an idle system. As for the
> object statistics, there is a serious question whether it is better to
> collect statistics regularly of use dynamic sampling, level 11 which would
> also udate the statistics tables. Unfortunately, not being a DBA any longer
> means that I cannot test. This suggestion should be tested, ideally in a
> development or test systems. You probably don't want to be the most
> interesting DBA in the world and do your testing in production. There is an
> old parody of Dos Equis commercial which says "I don't test often, but when
> I do, I do it in production". Testing in production never ends well, no
> matter how interesting the DBA.
>
> Regards
> On 3/25/19 12:56 AM, Cee Pee wrote:
>
> List,
>
> I was reading up on system stats and came across this link:
>
> https://blogs.oracle.com/optimizer/should-you-gather-system-statistics
>
> Here are some of the things the author says:
>
> 1. "if you are at a decision point and you need to choose whether to
> gather them or not, then in most cases you should use the defaults and *not
> *gather system statistics."
>
> Doesnt setting systems help a lot these days esp with faster IO devices.
> Do the listers collect system stats in your environments, test. prod, etc?
>
> 2. "there is at least *some *management or procedural overhead required
> to maintain them"
>
> 'Maintaining' stats? I thought once we set the system stats we leave it
> out there forever without touching it?
>
> Thanks all,
> CP
>
> --
> Mladen Gogala
> Database Consultant
> Tel: (347) 321-1217
>
>

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