In STS 4 there is constant, high cpu usage along with large amounts of memory used when Code Mining is enabled along with Live Boot Hint Decorators for certain spring boot projects. I have a very small project that can reproduce it with released STS 4 (or Eclipse with STS 4 plugin) on Windows 10. Nightly builds of both show the same pattern.

Steps to reproduce:

Windows 10 - fully patched
STS 4 (or latest Eclipse with STS 4 plugin)
STS configured to run with Java 1.8 JRE with tools.jar added to the lib directory or Open JDK 11
Enable Code Mining
Enable Live Boot Hint Decorators
Import the uploaded database-demo project archive

Open all three java files in the IDE:
DatabaseDemoApplication.java
PersonJdbcDAO.java
Person.java