This page summarizes our experience with tuning Polygraph benchmarking environment and gives a few useful OS dependent tips. Whether you need to apply all patches discussed here depends on many local factors. However, if you are doing high request rate benchmarking, you probably must tune your environment to get meaningful (or any!) results. Finally, please note that some of the patches are not meant to be used on general-purpose workstations.

If you have your own benchmarking tricks not covered here, please share them with us.

FreeBSD is our platform of choice for Web Polygraph. As with any other operating system, some tuning is required to produce meaningful results on high load tests.

• FreeBSD-3.3 instructions (will be used during the second cache-off)
• FreeBSD-3.1 instructions (being used in our benchmarking Lab)
• FreeBSD-2.8 instructions (used during the first cache-off)

They say that Linux is the choice of GNU generation. Linux/GNU distributions are indeed very popular and may be the best choice, especially if you want experimental driver support for just-released hardware or just want to look cool.

The most notorious configuration problem reported on Linux is increasing the number of file descriptors available to an application. The solution will depend a lot on the version of the Linux kernel. Linux design requires file descriptor limits to be updated in several places. If you forget to update or recompile one of the kernel modules or library, you will not get the desired effect. In the latter case, various diagnostic and configuration tools may tell you that you have the desired number of file descriptors when in fact you do not. In other words, do not trust your eyes and rely mostly on the performance of your application and on what that application reports.

Here are a few links with the instructions on how to increase the number of file descriptors on Linux. If you have questions, you probably want to direct them to the wonderful authors of these helpful pages; we are not Linux gurus. Some of the links below appear to be Squid specific, but kernel modifications ought to be the same regardless of the application.

• Dancer's instructions for Linux 2.0.36.
• Henrik Nordström instructions for Linux 2.2.x.
• Squid FAQ entry for 2.2.x and 2.0.x kernels.
• Janet Web Cache FAQ entry for Linux 2.2.1.

You may also search for the word ``Linux'' in Polygraph mailing list archive. A few specific step-by-step instructions have been posted there.