In a table, (how can you/should you have to) manage your primary keys so that they remain continuous? For instance, if you have a table of users and your primary key is a user id, then when a user is deleted, say user 5, then your table will read 1,2,3,4,6. If this process is then multiplied, the gaps will be more dramatic. Is this something to worry about? if so, how do you fix it?