In Oracle Database 12c, Multitenant is a pure deployment choice. It is possible to upgrade from, say, Oracle Database 11g to Oracle Database 12c, non-CDB and stop there. Of course I wouldn't recommend it! I would encourage every customer to take the next step and adopt that database as a PDB by plugging it into a CDB. Note that if that is the only PDB plugged into the CDB this is what we call the single tenant configuration (using the multitenant architecture). The single tenant configuration does not require nor trigger the Multitenant licensed option.
So, in summary, with Oracle Database 12c you have three choices:
- Non-CDB (the old architecture).
- Multitenant architecture in single tenant configuration (one PDB per CDB). No license required.
- Multitenant architecture with multiple PDBs per CDB. Requires licensed option but of course you can manage many as one and get all the other benefits.An interesting question of course is, what's the point of the single tenant configuration? Well, there are still some advantages:
- You will be able to upgrade (beyond 18.104.22.168 - say to 22.214.171.124) via unplug/plug, which we expect to be significantly faster than a "full upgrade".
- Unplug/plug has intrinsic value as what my colleague, Distinguished Product Manager Bryn Llewellyn (author of the excellent Multitenant White Paper), calls "Third generation Data Pump". In other words, if Data Pump (using "full database" exp/imp) is valuable (and we must assume that it is!) then unplug/plug is yet more valuable for the same use cases. This by no means implies crossing Oracle Database software version. But that is among the use cases (also for Data Pump, of course).
- You can clone from a PDB in a single tenant configuration CDB into a different, as yet empty, CDB.
- It enforces the "separation of duties" between the CDB Admin and the PDB Admin.
- Eventually there will only be one architecture and if you don't pay for the Multitenant option you'll have to run in single tenant configuration. Get used to it now!
Each of these is an advantage over the non-CDB architecture. What I like about the single tenant configuration is that, even without requiring a license, it demonstrates a few of the key benefits of the new multitenant architecture. In this way customers can become confident of the new capabilities at no cost. Of course many of the key cost-savings benefits - CapEx reduction by consolidating multiple applications per server and OpEx reductions by managing many as one (retaining granular control where appropriate) only come from the true multitenant use case. But the single tenant configuration is a great way to dip one's toes in the water.
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