Oracle Database - Patching Model 18c

With the advent of 18c new release, Oracle completely re-thought of Patching and the way releases are sent to the customer 

Key highlights here are 

1. Yearly new major release
2. Quarterly new release update
3. Quarterly new release update revision

So what are these

Let's understand by example

1. Oracle released 18.1.0 release in 2018 Production (yearly release)

2. In April they released 18.2.0 
This is a release update.  It contains all the regressions,  security fixes, optimizer and functional fixes
3. Similarly in July they will release 18.3.0
This is again a Release update

A release update is quarterly 

4. In July they will also release 18.2.1 - a patch or a release update revision (RUR)
 A RUR is like a patch and is installed on top of existing Release Update, however it does not contains any Optimizer or Functional Fixes, they are only present in Release Update. 

5. Now in October they will release

• RU - 18.4.0 
• RUR - 18.3.1
• RUR - 18.2.2

6. finally Every year a new release 19 in 2019, 20 in 2020. 
The licensing aspect is to be decided by Oracle, that is which all releases are going to part of same license set.

Here is what I mean in a photo. 
If you notice the # of lines corresponding to each feature (functional, optimizer etc), you will notice they are only added as part of Release updates and not part of Release updates revisions on the release. 

However if you do a sum  for example 
18.4.0 and 18.3.1 (sum of second 2 decimal places), the fixes for regressions and security are same (but not optimizer and functional)

Upgrades (Release and RU) and patches (RUR) ?
A complete timeline example of Oracle releases and upgrades is below - 

You can upgrade in the same column from bottom to top (i.e keep adding features, you cannot remove any)
Upgrade (or patch) from left to right. All the green arrows are supported and the red ones are not.