During installation, small text file named PegaRULES_Extract_Marker.txt is created in the temporary files directory, recording the date and time that all libraries and functions were extracted into Java and compiled.
You can force re-extraction and recompilation of all the libraries and functions on one node by deleting this file. The extraction and compilation occurs the next time PRPC is started on that node.
This start-up step also clears specific disk directories: Deletes all generated Java files (from PRGenJava and PRGenClass directories) before the extraction Clears the StaticContent directory, which includes ServiceExport Clears the lookup list caches
Yes, this will have an impact on the cache tables on the DB, hence whenever you clear the extract marker and restart the cache tables like assembledclasses gets populated and this will impact the performance till you have everything in the cache.
Whenever you install a hotfix containing any changes to the Java class of the PRPC code base it needs to be recompiled and available in the cached tables, hence support suggest you to clear the extract marker file and restart the server instance. But you can make sure if the fix contains only changes to the PRPC rules and not to the java code, you can skip the same
It is not mandatory to clear PegaTempDir everytime after the jvm restart, if you want to clear the Lookup List Cache(i.e.PegaTempDir) data during the restart then only you need to perform this action. Generally you can see this step during the hotfix installation process.