Re: To estimate maximum active sessions on my oracle database is reasonable to the approach?

The number of affordable sessions primarily depends on what the sessions are doing and the amount of available resources. To rephrase it, it depends on the meaning of the word "affordable". It also depends on the meaning of the word "is", as one of the former US presidents is known to have said. In addition to that there is a dependency on the database configuration. Pooled connections and shared servers can significantly increase the number of concurrent sessions. In other words, reasonable answer can only be provided by some type of benchmark.

On the other hand maximum usage since the instance startup means "the maximum concurrent sessions", since the instance was started up. For me, the phrase "since the last startup" usually means "in the last 3 months", since we install DBRU 2 weeks after they are published. That IS the number you are looking for: the maximum simultaneous sessions that have been logged into the database, since the last startup.

As for that monstrosity of the script, I would advise using sar, vmstat and iostat to measure CPU consumption, memory consumption and disk consumption. Your "affordable sessions" will only be affordable as long as you don't start swapping and burning 80% of CPU. I tend to believe the OS tools more than the values from the Oracle performance tables. I remember more than one case of inconsistent values in the performance tables.

On 10/31/21 02:21, Quanwen Zhao wrote:
> Hello MGogala 😉,
>
> I don't think that the column MAX_UTILIZATION in the view
> V$RESOURCE_LIMIT represents the maximum usage as you can see its
> description as follows:
>
> *Maximum consumption of this resource since the last instance
> start-up*.
>
>
> In other words the key information is "since the last instance
> start-up" instead of the *AFFORDABLE* maximum value on oracle
> database, it just indicates that oracle once increased to the value
> that is greatest than ever before (perhaps the value is beyond the
> affordable scope of oracle database). Now I need to find out the
> *CRITICAL* value (eg, the maximum concurrent connections in my case).
>
> BTW I use this SQL script to test AAS and Logic CPUs -
> *https://github.com/guestart/Oracle-SQL-Scripts/blob/master/awr_trend/acquire_logic_cpus_union_aas.sql*
> <https://github.com/guestart/Oracle-SQL-Scripts/blob/master/awr_trend/acquire_logic_cpus_union_aas.sql>,
> you can see the section with *"in Real Time"*.
>
> At this moment I realized my approach need to be rectified because AAS
> is related to DB Time but DB Time just contains the time spending on
> *FOREGROUND* processes, unfortunately the SQL query *select count(*)
> from v$session where status = 'ACTIVE';* includes the BACKGROUND and
> FOREGROUND processes. Please waiting for a while ...
>
> Best Regards
> Quanwen Zhao
>
> Mladen Gogala <gogala.mladen_at_gmail.com> 于2021年10月31日周日
> 下午12:35写道：
>
>
> On 10/30/21 23:35, Quanwen Zhao wrote:
>> Hey my folks and colleagues 😉,
>>
>> For estimating the *maximum concurrent connections* on my oracle
>> database server I did the some work as follows:
>>
>> * Acquiring *Average Active Sessions* & *Logic CPUs* in Real Time;
>> * Retrieving the *current concurrent connections* on view
>> *"v$session"*;
>>
>> Via the above two steps I've got some data, such as, aas value is
>> *3.66* and logic cpus are *192*. Next I've got the current
>> concurrent connections (*61*) by running this SQL statement:
>> *select count(*) from v$session where status = 'ACTIVE';*
>>
>> Thus I am able to estimate the maximum concurrent connections
>> using the following formula: aas value / logic cpus = current
>> concurrent connections / maximum concurrent connections. That is
>> to say, *3.66 / 192 = 61 / maximum concurrent connections*, so
>> which is *3200*. Is it reasonable to this approach?
>>
>> Best Regards
>> Quanwen Zhao
>
> That is approximately as efficient as hunting grizzly bears with a
> sewing needle. There is a table named V$RESOURCE_LIMIT which has
> MAX_UTILIZATION column. The table is described here:
>
> https://docs.oracle.com/en/database/oracle/oracle-database/12.2/refrn/V-RESOURCE_LIMIT.html#GUID-AC182B2E-8D26-43D7-A356-BE1F15BDF152
>
> Thanks for reminding to switch my documentation bookmark from 12.2
> to 19c, I'll do that tomorrow. As for the grizzly bears, everybody
> knows that they should only be hunted with your bare hands. The
> same applies to their black cousins.
>
> --
> Mladen Gogala
> Database Consultant
> Tel: (347) 321-1217
> https://dbwhisperer.wordpress.com
>
> -- http://www.freelists.org/webpage/oracle-l
>

-- 
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com


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