Array usage affecting server

Hi. When a database query is done and the results are put into an array, what are the resources used? I name all arrays differently and was wondering how it would affect the performance of the server if many people connected with many arrays being full. I am assuming the array gets 'dropped' when you connect to another page but if I keep on the same page using PHP_SELF? Basically I am just trying to find out what is the best way of using arrays without using all the servers resources. Thanks Kevin