@mukkarramS - During Pega installation we specify a temp directory in which pega loads all the generated class into the application server and adds them to the classpath. It also contains various other folders and subfolders meant for different usage. In this folder you will find a file by the name PegaRULES_Extract_Marker.txt file. 

If you do a restart then contents in this directory is maintained and only App server is restarted

If you do a restart after deleting the file PegaRULES_Extract_Marker.txt in the temp directory then during restart the temp directory contents are again reloaded from database.