Question relating to trace/debug/log OTP features
Wed Dec 10 08:21:11 CET 2003
I'm puzzled by the many facilities OTP contains to generate trace-,
debug- and log information. Perhaps someone could point me to an
overview/tutorial of what the mechanisms are that you recommend I use
for a brand new development. What's missing the most in the docs (or I
could not find it) is how the various mechanisms relate to each other
(e.g. which ones are basic services that high level trace/log services
leverage, which ones are "old" and still there for backwards
Specifically I need 3 things:
1. error/warning/info/detail messages that the end user should see in
2. debug information.
3. more debug information (free form, not tied to gen_*
For (1) I use error_logger currently, is there an alternative I should
consider? Sometimes I'd like to be able to show customers more levels
of granularity (currently error and info are available, I need warning
and detail as well) without having to resort to the debug level data in
(2) and (3). Is there a way to add another level to the current 2
(error/info/...)? Is there an Erlang/OTP philosophy to only having 2
For (2) I use sys:trace(Mod,true) to enable *DBG* messages for gen_*
behaviour and for my own (along section 6.2.1 "Special processes" of
the "design principles" doc). However sometimes I'd like to show
additional *DBG* messages of my own in callback modules that I pass to
gen_* behaviour - how can I do that (i.e. what do I call inside the
callback module to generate a *DBG* event?
For (3) I currently use a macro to enable/disable io:format calls (the
old style "recompile with debug" story). Is there a facility in OTP
that I can use to enable dumping of debug information at runtime w/o
recompiling (I'm quite happy to accept the performance penalty, my
application is not performance critical)? E.g. can I use sys:trace in
arbitrary code and through that get the dynamic enable/disable?
In addition, does anyone have examples code or tutorial on the
following (or advice as to when to use):
- disk_log and disk_log_wrapper (i.e. vs. the error_logger info/error
- seq_trace and the observer/ttb (R9C). Specifically are seq_trace and
ttb the basis and observer the visualizer? How do I invoke the observer
(R9C docs are silent on that)?
- How does et (et_collector, selector, viewer) relate to the
observer/ttb/seq_trace facilities? How does it relate to sys:trace?
I'm hoping that some OTP expert can help me understand these facilities
and their relation and when to use what (ideally by
example/experience). Perhaps someone could talk about the OTP history
and how the many powerful mechanisms were motivated (various projects,
Thanks in advance for helping me navigate the Zoo.
A distributed system is a system in which I can't do my work because
some computer has failed that I've never even heared of . -- Leslie
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