What is the best practice? use different database for every users or use same database with userid coloumn

What is the best practice? use different database for every users or use
same database with userid coloumn

What is the best practice? use different database for every users or use
same database with userid coloumn.
I am working on mysql database and php. I having a little bit confusion
about my project.
My project is user based. If a user has been registered then he can store
data on a many tables. I have created all tables with userid column to
find data for particular user. But now I am thinking about it if tables
having huge amount of rows then my project will getting slow to fetch
records.
Now the confusion is "what is the best practice use different database for
every users or use same database with userid coloumn."