MySQL: How many queries per page is too many? [closed]

Question

I'm new to MySQL and something that's quickly becoming obvious to me is that it feels considerably easier to create several database queries per page as opposed to a few of them.... but I don't really have a feel for how many queries might be too many, or at what point I should invest more precious time to combining queries, spending time figuring out clever joins, etc.

I'm therefore wondering if there are some kind of "mental benchmarks" experienced folks here use with regard to number of queries per page, and if so, how many might be too many?

I understand that the correct answer in any context is related to what's needed to satisfy an application's functional requirements. However, on projects where client requirements may be flexible or not properly set, or on projects where you as the developer have full control (e.g. sites you develop for yourself), you may be able to negotiate between functionality and performance... basically, to just cut trivial features if coding requirements impact performance and you're unable to optimise it any further.

I would appreciate any views on this.

Thanks

Answer 1

There's no set number, "page" is arbitrary enough - one could be doing one database task while another could have 2 dozen widgets each with their own task.

One good rule of thumb though: the moment you put a SELECT inside a loop that's processing rows of another SELECT, stop. It might seem fast enough early on, but data tends to grow and those nested loops will grow exponentially with it, so expect it to become a bottleneck at some point. Even if the single query ends up being significantly slower, you'll be better off in the long run (and there's always stored procs, query caching, etc).