Is my site too big for Shared or Reseller Hosting
Shared hosting is relatively cheap, and that's because you are sharing a machine with large resources amongst many small sites each using only a small tiny proportion of those resources.
So what happens as your site gets more popular?
Well, when it uses too many resources it can no longer be sustained on a shared hosting server.
UnixGuru has a server with 32 CPU Cores.
A user is allowed to use up to 100% CPU (equivalent to one core).
On that basis, it would only take 32 users maxing our their CPU to max out the server.
Now given that 16 users may pay £2 a month, that means that £64 of revenue for UG, could use a server with costs hundreds of pounds.
Peaks and Troughs
We don't mind a website using large amounts of resources for a small period, if they get mentioned on a popular site like Slashdot, Reddit, Twitter or Facebook etc.
If however, a site starts to use a large amount of resource continuously, then the owner of the site will be asked to optimise or move the site,
Alternatively, they can pay for an "Elastic-Sites hosting account" to house the site.
As a guideline, if your site uses more than 5% CPU on average for longer than 30 minutes of the day, then it is a candidate for being moved or upgraded. However, it is usually twice this level before we start to worry,
If a site gets too resource heavy for us to host on shared hosting we will send the user a message telling them so.
If within 7 days that site is not under control, it will be suspended.
This is done to protect the other sites on the server, which are adversely affected by the busy site using too much resource.