Optimizing Unix for Performance

Optimizing the performance of computer systems has always been an art relegated to a few individuals who happen to have the "right skills." UNIX systems have not escaped this syndrome. It is rare to find anyone who knows how to instrument the system, let alone tune it. This is by no means a fault of the general user community. The problem turns out to be rather complex, requiring good knowledge of computer architecture, UNIX design, and performance-monitoring tools. Due to a lack of standards in the system performance management area, vendors often take liberties with substituting, enhancing, or altogether removing system-monitoring tools. Even when a familiar command does exist on a system, it may have subtle differences that can easily mislead you. One such example is the unit for some of the fields. In a typical manual page, you see frequent references to units of "blocks" or "pages." Yet there rarely is an indication of how big these things are. As you will see later in this book, a page can be anywhere from 512 bytes to 8 kilobytes, making it very hard to interpret such data correctly. Beyond the tools, there are also a number of limitations in the UNIX architecture itself. Without knowing about these deficiencies, you could easily chase the wrong problem. A classic example is when people blame the hardware instead of UNIX and vice verse. In the end, we hope that you do not misinterpret our criticisms of one of the best operating systems around. Perhaps our only excuse for pointing out these deficiencies stems from a wise saying that states: If you cannot criticize something, you do not understand it well enough! I.1 General Style In this book, we take a system approach to performance optimization by covering everything from user applications all the way down to the hardware. At the same time, we try not to assume that you have a strong background in either hardware architecture re or UNIX internals or, for that matter, extensive experience with UNIX itself. Just in case you have dabbled seriously in any of these areas, we explain each topic in a separate chapter, making it easy to skip over them. You will probably also notice that we have dedicated considerably more space to analysis than to simple cookbook procedures. While cookbook procedures do have their place (and we have included a fair number in this text), they do not have any use unless you know when to use them. Armed with an in-depth knowledge of what is going on inside your system, you will be better able to identify the true nature of performance bottlenecks in your system. As a bonus, you will be in a position to solve a wider set of problems than what is covered here. In a departure from other texts on this topic, we have taken a very pragmatic view by emphasizing modern techniques for tuning UNIX systems. Had this book been written in the early 1980s, we would have focused heavily on how to modify the operating system parameters to either squeeze the last byte out of it or save a few CPU cycles. The advice would have been sound in that time frame due to the fact that the average machine was well under 5 MIPS and had around 8 megabytes of memory. Any amount of savings would have seemed significant. Current CPUs are orders of magnitude faster with tens or even hundreds of megabytes of memory. The result is that the benefits of many of these optimization techniques are simply "lost in the noise." So, rather than relying on obsolete advice, we focus on higher-level approaches to system optimization. These tacks include optimization of the system hardware, general techniques for resource utilization, and more optimal usage of the system and network. Alas, old habits die hard, and users have a fondness for "poking" values into their system. For this reason, we also cover those parameters and tuning methods that have at least some noticeable impact on the system performance. But we would like to recommend again that you stay awayMajidimehr, Amir H. is the author of 'Optimizing Unix for Performance' with ISBN 9780131115514 and ISBN 0131115510.