Re: Multi-Tenant Question - Oracle chose HIGH COUPLING - why?

Hi Chris,

let me see if I can clarify these questions. See inline responses...

On Jul 19, 2016, at 7:49 AM, Chris Taylor <christopherdtaylor1994_at_gmail.com> wrote:

> As I'm learning the multi-tenant technology with 12c, I'm struck by the following ODD choice that Oracle made. I feel certain there's a reason (and perhaps a good one) why Oracle chose to increase COUPLING instead of building independent, low dependence modules?
>

Actually it was not an Oracle decision per se, but Oracle responding to customer demand.

> Here's what I'm talking about: (Note: 2001512.1)
> Oracle recommends the creation of a container database with all options as that configuration
> rules out any option related mismatch problems while unplugging and plugging a PDB from one container to another.
> However customers have often asked whether it is possible to create a container database with a subset of options.
> Although it is still recommend to create a CDB with all options, this document outlines a supported method of creating a
> CDB with the options that the customer chooses to install.
>
> And (Note: 1616554.1)
> Oracle generally recommends that a CDB should have all options installed
> in order to avoid any issues with the plug-in of a PDB from another environment.
>
> It seems to me that this over complicates the situation unnecessarily but I'm sure there must be a good reason.
>
> Why doesn't it make more sense to have the CDB as a "brain" that doesn't really care about what options are installed in a PDB. Why does the CDB need all the options installed to properly plugin another PDB that has some "x" option installed?

This was exactly the initial intent where the CDB, as the �brain�, which has all of the options available such that any PDB plugged in that requires a specific option would have that option available. This avoids the complexities of placement and maximizing consolidation density where if this were not the case, you would need to map PDBs to CDBs providing the specific option and consolidation density would be negatively impacted. ULA customers obviously have no problem w/ this, however, other customers did not want to incur the licensing implications for all options. Hence, the MOS note which describes the cumbersome 12.1 steps limit the options configured in the CDB. This gets much, much better in 12.2 in terms of ease of configuration and licensing.

>
> Wouldn't it make more sense for the CDB to ambivalent about what options the PDB has and just be the controller instead of having these created dependencies between the CDB and the PDBs it controls?
>

The CDB cannot be �ambivalent� to the options required by the PDB. The architecture is what we refer to as in-database virtualization where we have a pristine, master copy of the Oracle data dictionary in CDB$ROOT. For this reason, CDB$ROOT will have all dictionary references for all options configured. PDBs use object and/or metadata links to resolve inter-dictionary dependencies between the PDB dictionary and the CDB$ROOT dictionary. It is required that the PDB have all or a subset of options installed in the CDB$ROOT. Otherwise, you get the plug in violation warning until the dependencies are resolved.

> It just seems like this should have raised some engineering red flags along the way unless there's something I'm not seeing.

Let me know if this answers your questions. This dictionary relationship is really the core of Multitenant and gives us many opportunities for future development.

thanks,
jpm

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> Chris
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