How Much Memory Can MySQL Use?

There is a hard upper limit on the amount of memory that can possibly be available to MySQL on any given system. The starting point is the amount of physically installed memory. If your server doesn’t have it, MySQL can’t use it.

You also need to think about operating system or architecture limits, such as restrictions 32-bit operating systems place on how much memory a given process can address. Because MySQL runs in a single process with multiple threads, the amount of memory it can use overall might be severely limited by such restrictions—for example, 32-bit Linux kernels limit the amount of memory any one process can address to a value that is typically between 2.5 and 2.7 GB. Running out of address space is very dangerous and can cause MySQL to crash. This is pretty rare to see these days, but it used to be common.