Web Application: Disable User Multiple Voting

Question

Algorithms

For the first time I am writing a web application and there are questions about how it would be better to do it.

Here for example on Habré for a topic it is possible to vote only once. How it is more correct to implement it? Store with each topic a list of voted users? And if there are a lot of objects, for example, comments?

Answer 1

Make a vote using paid SMS messages, and let them vote as much as they want :)

Answer 2

Store
user_id+topic_id
user_id+comment_id
don't know how else

Answer 3

keep a syslog in which to write all voting events (and maybe others at the same time, such as creating messages / comments)
will solve the problem of both one-time voting and “once a day” voting