how google facebook or other bigcompanies stores username and password

Question

if they use only table like 'users' so there will be millions of fields then the fetching will be slow how they manage to log in so fast

Answer 1

there are many different approaches .. most use distributed db structure to enhance performance and to enable api services.shortly seperating huge dbs will increase speed performance security stability blah blah blah...

but in any case this happens when you became big enough to need more servers to respond over 1000 request at same time . so to that day you keep the user table in same database

Answer 2

They have much of tables, databases and of course, they have server farms to distribute all data