I am creating a social networking site that will be open to the general public and will expected to host a large number of users. The information of each user will be stored in a MySQL database, and pages will be written in PHP.
My question is this: What do big sites such as Facebook, Yahoo, Stack Overflow use for their primary and unique keys to keep track of a large number of data?
For an example, a table such as:
PK, Unique_Id, User_Id, F_Name, L_Name, Date_Created, DEL, etc...
How can I give each user in this table their own unique_id they can have for themselves that will be reasonable? What format should a unique id be in to be beneficial? How should I manage the primary keys? Let the pk start from 1 and increment each time?