Introduction to Performance Testing

1.1 Why Performance Testing?

Main purpose of performance test is not to find bugs but to eliminate bottlenecks and establish a baseline for future regression testing.
For a Web application, you need to know at least two things:
• expected load in terms of concurrent users or HTTP connections
• acceptable response time
Once you know where you want to be, you can start on your way there by constantly increasing the load on the system while looking for bottlenecks.
To take again the example of a Web application, these bottlenecks can exist at multiple levels, and to pinpoint them you can use a variety of tools:

• at the application level, developers can use profilers to spot inefficiencies in their code (for example poor search algorithms)
• at the database level, developers and DBAs can use database-specific profilers and query optimizers
• at the operating system level, system engineers can use utilities such as top, vmstat, iostat (on Unix-type systems) and PerfMon (on Windows) to monitor hardware resources such as CPU, memory, swap, disk I/O; specialized kernel monitoring software can also be used
• at the network level, network engineers can use packet sniffers such as tcpdump, network protocol analyzers such as ethereal, and various utilities such as netstat, MRTG, ntop, mii-tool
When the results of the load test indicate that performance of the system does not meet its expected goals, it is time for tuning, starting with the application and the database. You want to make sure your code runs as efficiently as possible and your database is optimized on a given OS/hardware configurations. Another common goal of performance testing is to establish benchmark numbers for the system under test.