Hints for computer system design, Published by ACM . Butler W. Lampson, Howard E. Sturgis, Reflections on an operating system design, Communications of. Butler Lampson’s “Hints for Computer System Design”. I recently read Butler Lampson’s immensely wonderful paper “Hints for Computer. Butler Lampson as recently updated his paper. Slides: Slides/Hints%20and%20principles%20(HLF.
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Error recovery at the application level is absolutely necessary for a reliable system and any other error detection or recovery is not logically necessary but is strictly for performance. Many of the hints help us to think about the trade-offs between simplicity, consistency, correctness, and completeness.
Lampson gives the example of parsers that do context-free recognition but call out to client-supplied semantic routines to record the results of the parse. Make it fast, rather than general or powerful. Especially, it should not promise features needed by only a few clients, unless the implementer knows how to provide them without penalizing others.
Hints for Computer System Design () [pdf] | Hacker News
The only true reliability is end-to-end, though relying on this exclusively can hide severe performance defects that only appear when the system is under heavy load. As the system evolves over time, …there is a constant tension between the desire to improve a design and the need for stability or continuity. Shed load to control demand, rather than allowing the system to become overloaded.
For each, Lampson gives examples from real systems. Doing things incrementally almost always costs more… Also, batch processing permits much simpler error recovery. It is much better to have basic operations executed quickly than more powerful ones that are slower of course, a fast, powerful operation is best, if you know how to get it.
Obviously, it is easier to program and modify a system if its parts make fewer assumptions cokputer each other. The designer usually finds himself lampspn in a sea of possibilities, unclear about how one choice will limit his freedom to make other choices, or affect the size and performance of the entire system.
For basic interfaces shared by many parts of the system, stability is highly desirable. A system cannot be expected to function well if the demand for any resource exceeds two-thirds of the capacity, unless the load can be characterized extremely well. Split resources in a fixed way if in doubt, rather than sharing them. Fill in your details below or click an icon to log in: Use an append-only log to record the truth about the state of syxtem object. As I read compkter the paper, I was struck by how much his advice applies to building just about any kind of complicated software system, including frameworks.
Making a system reliable is not really hard, if you know how to go about it.
Joe Duffy – Butler Lampson’s “Hints for Computer System Design”
Make actions atomic or restartable. This also applies to processing when resources are limited: The purpose of abstractions is to conceal undesirable properties; desirable ones should not be hidden. You are commenting using your WordPress.
An interface should capture desiign minimum essentials of an abstraction. It may have been written inbut the fundamental challenges in building computer systems that Lampson outlines still ring very true today: And there is tension with the desire not to hide power.
The external interface that is, the requirement is less precisely defined, more complex, and xomputer subject to change.
Hints for computer system design
How then should we think about the trade-offs between these requirements? To use the technique, record every update to an object as a log entry consisting of the name of the update procedure and its arguments.
Firstly, beware of rushing to create fancy high-level abstractions: For this to work, operations must also be idempotent, the arguments must be values which can include references to immutable objects. Do one thing at a time, and do it well.
The client of your interface should not be surprised by unpredictable behaviour:. A fast, basic interface beats a cumbersome higher level one: The client of your interface should not be surprised by unpredictable behaviour: An cojputer should capture the minimum essentials of an abstraction. Leave a Reply Cancel reply Enter your comment here You are commenting using your Twitter account.
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Email required Address never made public. The procedure must be functional ; when applied to the same arguments it must always have the same effect… By induction this means that a sequence of log entries can be re-executed, starting with the same objects, and produce the same objects that were produced in the original execution.
Excerpts from Butler Lampson’s “Hints for Computer System Design”
And be sure that you know how to make it fast. Usually it turns out that the powerful operation is not the right one. In the paper, Butler offers many principles backed by concrete examples illustrating tradeoffs between functionality, speed, and fault-tolerance, drawn mostly from his experience building operating and distributed systems.
One way to combine simplicity, flexibility, and high performance is to focus only on solving one problem, and leaving the rest up to the client. Pushing towards maximum utilisation can drastically degrade services.