Got a question on how best to design a database. I am using MySQL on a CentOS server.

Lets say I want to design an online, web based system where different users will store data in identical designed databases. Each users data must be protected from access by other users. I know I can create seperate databases and secure each of those databases by a username/password. (at lease I read that in another forum, haven't tried it yet) Is that the best way and have a whole bunch of seperate identically laid out databases? Or, is it better to create one big database and then key each table record to the user. Can you lock a record by user? Multiple database would be the easiest way but is there a limit on how many databases you can create? Will having several databases bog down performance?

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