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
