Thinking about uses for (system) activity tracers
July 20, 2008
System activity tracers are a hot topic, with the best known one being Sun's DTrace. In thinking about this issue recently, I believe that there are three sorts of questions that they can be used to answer, or at least that I'm interested in having answered:
The latter is important for solving specific problems; often you know roughly what is going wrong and what program is responsible, but you don't know why and how it is going wrong because you can't see the program's decision making process or even the information it is getting to make the decision. For example, consider 'I can't NFS-mount a filesystem that I think I should be able to'.
In theory you could deal with this by having programs optionally log a lot of information. My personal feeling (partly from having dealt with programs that did copious logging if asked) is that it is better to have a single central interface for deciding what you want to watch and log than to try to give every program options to control all of this; it just scales better, and it's probably easier for program authors too (since they just have to make some hooks available, instead of building a dynamically reconfigurable debug logging system).
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