Row Level Security in BO: Performance

Hi,

I was recently asked a very interesting question and could not find any useful answers, so decided to post it here.

The question is:

How does the query engine process Row level security in BO? Does it fetch the data first (which seems right) and then fail the condition or is it vice versa?

Will having a row level security implementation in the universe impact the performance of the reports?

Would like to know your insights on the same.

Thanks and regards,

Vinayak