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

Yes, actually benchmark is absolutely able to get the maximum concurrent connections my expected. You know, oracle production system has been online and it's impossible to do it. Here I have to estimate it using my approach previously mentioned.

The max AAS value is *2.98* from ASH in last 1 hour and logic cpus is *192*, and current concurrent connections is *60*, eventually I get the maximum concurrent connections that is *3866* according to my formula. By the way the attachment is the SQL script I use.

Best Regards
Quanwen Zhao

Mladen Gogala <gogala.mladen_at_gmail.com> 于2021年10月31日周日 下午2:55写道：

> 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) 321-1217https://dbwhisperer.wordpress.com
>>
>> -- http://www.freelists.org/webpage/oracle-l
>
> --
> Mladen Gogala
> Database Consultant
> Tel: (347) 321-1217https://dbwhisperer.wordpress.com
>
>

--
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application/octet-stream attachment: Active_Sessions__in_ASH__including_BACKGROUND_processes_in_Last_1_Hour.sql