when i apply "alter database tempfile /path_to_temp01/temp01.dbf resize 500M;" command, i can see via oem that the size takes a value what i set. But in the operating system environment (which is linux) i can not see the changed size with du -ha command. it remains constant. what is the reason of this? will this situation be a problem for the temp file? and How can i calculate the ideal size of this file?