Hi,
Welcome to the community!
The first thread you link to is generally correct. Specifically,
However, it is worth noting that in the intervening 2 years, we added analysis caching for C, C++ and Objective-C only.
The second post you link to is about a feature which was dropped before the current LTS. Nonetheless, IIRC, analysis also covered the entire code base even with that feature.
Regarding the speed of analysis, that’s going to depend entirely on the size of your project and the resources available to analysis.
I have seen some people do some scripting tricks to limit the sonar.sources value for a PR to only those files changed during the analysis. Aside from being fiddly doing it this way runs the risk of missing some issues, so we don’t recommend it.
HTH,
Ann