What is Performance testing in software?

• It is  a type of non-functional testing.
• Performance testing is testing that is performed, to determine how fast some aspect of a system performs under a particular workload.
• It can serve different purposes like it can demonstrate that the system meets performance criteria.
• It can compare two systems to find which performs better. Or it can measure what part of the system or workload causes the system to perform badly.
• This process can involve quantitative tests done in a lab, such as measuring the response time or the number of MIPS (millions of instructions per second) at which a system functions.
• Very simply we can put the difference between Volume, Load and stress testing as:
  Volume Testing = Large amounts of data
  Load Testing = Large amount of users
  Stress Testing = Too many users, too much data, too little time and too little room.