Does requirement on the number of maximum concurrent visitor make a great difference on coding?

Question

Will the code be much different if requirement on the number of maximum concurrent visitors is greatly different?

It is said as for code, developing a website that can endure 10,000
concurrent visitors is much different from developing a website that
can stand 1,000 concurrent visitors, is it true?

Does changing the code to adapt to a much greater concurrent visitors cost much time?

Answer 1

By 'code' you could mean many things.

Generally a page that spits out ordinary HTML could handle thousands of hits at a time without much penalty. Of course the router that manages that traffic may not be happy, but the amount of data in a plain-text page is minuscule compared to the demands of streaming video, for example.

Bandwidth is often more of a concern than coding, but the coding can be a factor. For example, if you write a back-end program in a scripting language like Perl through the CGI interface, a new perl interpreter will be created for each request. Although the requests themselves will be small, loading a new copy of perl for each would cause problems.

Modern server-side languages have taken steps to alleviate this problem.

Apart from bandwidth, the problem now is likely on the data end of things. Many sites today rely on a relational data server on the back end. Modern databases (not access, that's for sure) can handle thousands of concurrent users, but theres always a risk that two users will look for the same data at once, which can cause problems. If remote users are allowed to update a database, things can get really hairy. Sometimes delays are introduced artificially into the system to avoid concurrent update problems.

Answer 2

It depends on too many things to give you a full list here, but basically, the backend should be robust, with possible load-sharing amongst multiple CPUs or even servers, even if running same app, minimal drag on the server as possible, keep variable names short to keep transmission to minimum, and all that. However, coding itself, unless extremely badly written, is usually NOT a bottleneck when it comes to max concurrent users.