Re: limiting number of sessions in multitenant PDB

The sessions parameter is separately settable from processes. http://docs.oracle.com/database/122/REFRN/SESSIONS.htm#REFRN10197

I'd be *extremely* wary of consolidating 96 separate databases onto a single CDB with 96 PDBs unless those 96 single instance databases already share hardware. Consolidation *will* give you noisy neighbours, I see Franck already suggested using CPU_COUNT to control CPU usage, but even with a CPU_COUNT of 1 per server that implies an allocation of 48 cpus worth of resource.

Now it's likely of course that you'll be running RAC with a subset of databases on each node, rather than high core count servers, but then you need to plan for failure modes, what happens if one node of your 4 node RAC dies and you end up with each node having an unexpected 33% increase in workload.

Instead, it makes a lot of sense to plan your capacity (and outside of engineered systems there isn't a lot you can do about I/O) . I suggest starting with
https://ardentperf.com/2013/10/28/operationally-scalable-practices/ and thinking about to what extent the advent of PDBs and/or public cloud might mandate some different choices.

In addition, an often overlooked consideration is what to do about application downtime for database/server maintenance. With single server systems, you likely have one set of stakeholders to talk to, with 96 the problem could well become unmanageable.

I apologise if this is all well known to you. Even better if you've successfully consolidated at this scale and can write about it I'd love to read about what you've done.

On Mon, Mar 6, 2017 at 2:38 PM, Woody McKay <woody.mckay_at_gmail.com> wrote:

> In 13.2, is processes modifiable at the PDB level? Sessions is derived fro
> processes, right?
>
> On Fri, Mar 3, 2017 at 4:10 PM Franck Pachot <franck_at_pachot.net> wrote:
>
>> Hi,
>> The session parameter is PDB modifiable. It limits the number of sessions
>> in the PDB.
>> If you want to limit the concurrent sessions running in CPU then in 12.2
>> you can set cpu_count.
>> Regards,
>> Franck.
>>
>> On Fri, Mar 3, 2017 at 9:38 PM Woody McKay <woody.mckay_at_gmail.com> wrote:
>>
>> I'm looking at the new 12.2 multitenant on Linux 64x.
>>
>> So many new features and settings pushed down from CBD to PDB.
>>
>> Does anyone have the best solution for limiting the number of user
>> sessions per PDB?
>>
>> PDB level profile, resource management or lock down?
>>
>> Looking to put 96 customer SIDs into 96 PDB's and want to keep high
>> isolation.
>>
>>
>> Thoughts???
>>
>>
>> --
>> Sincerely,
>>
>> WoodyMcKay
>>
>> --
> Sincerely,
>
> WoodyMcKay
>

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Niall Litchfield
Oracle DBA
http://www.orawin.info

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