> Sometimes you just have to do joins across large tables. There just isn't any other way. Your query is going to run for 5, 10, maybe 30 seconds.
While that is true, I would speculate (based on my own experience, not any actual research) that it is far more common that users have an unoptimized query or database schema (perhaps it just needs an index to be created) which is taking tens of seconds to run but doesn't NEED to, than it is that users have a need for a complex query that cannot run faster than that.
So for MOST users, the best advice is to learn how to use analyze query and other database tools to optimize execution. Only if you ALREADY know that should you be considering moving to a read replica or some sort of distributed database.
While that is true, I would speculate (based on my own experience, not any actual research) that it is far more common that users have an unoptimized query or database schema (perhaps it just needs an index to be created) which is taking tens of seconds to run but doesn't NEED to, than it is that users have a need for a complex query that cannot run faster than that.
So for MOST users, the best advice is to learn how to use analyze query and other database tools to optimize execution. Only if you ALREADY know that should you be considering moving to a read replica or some sort of distributed database.