What is a "bottleneck" in a database?

A "bottleneck" in a database is the part of the system that limits its overall performance.

For example:

• the CPU can't keep up with the number of requests;
• a slow disk drags down reads and writes;
• insufficient RAM triggers frequent disk access;
• inefficient queries or indexes slow down data processing.

Because of that bottleneck, the whole system runs slower, even if every other component could otherwise run faster.