[erlang-questions] DTrace for Erlang
Jan Henry Nystrom
Tue Nov 13 19:20:56 CET 2007
You should probably have a look at the trace
functionality built in in Erlang(the trace bif with
the dbg library). That extended with a few bits and
bobs would probably provide you with most of you need.
G Bulmer wrote:
> Is anyone working on building an Erlang DTrace provider?
> I realise DTrace isn't available on all Erlang platforms, but now
> that DTrace is available Mac OS X (Leopard), as well as Solaris (and
> FeeeBSD), I feel it might be worth doing.
> About DTrace
> For those of you unfamiliar with DTrace, it is, basically, magic.
> DTrace provides facilities to trace any program, and many aspects of
> the OS kernel. It has several critical properties:
> 1. A program does not need any changes (no need to compile for debug,
> or anything like that). All existing programs work (to some extent).
> 2. When not DTrace'ing, the cost of being DTrace-able is almost zero
> (claimed < 0.5%) and this cost is already included (on Solaris & OS X).
> 3. It is 'secure', it honours the access control mechanisms of the
> host OS.
> 4. DTrace can cross process boundaries, and trace the kernel itself
> (if you have the appropriate security privileges)
> These features allow DTrace to be used in *PRODUCTION*.
> Put another way: it is straightforward to trace through a program in
> a user process, back out through the kernel, then into other
> processes. Tracing can be activated *after* a program has been
> deployed and started *without* changing the program or restarting it.
> DTrace overhead, when not tracing a program is (claimed to be)
> essentially zero, and DTrace costs when activated are (claimed to be)
> DTrace is programmable, with a scripting language a bit like awk but
> without loops; instead of awk text patterns, DTrace probes are
> pattern matched to trigger script actions. Scripting lets you
> correlate events across processes and the kernel, and scripts can
> process the data so that 'noise' can be filtered out. For example, it
> is feasible to trace from an incoming HTTP request through a web
> server, through the kernel, to an application server, and back again
> and correlate many concurrent flows. You might want to time that end-
> to-end flow, or gather intermediate timing, or watch for a particular
> access to a specific file, or ..., and the scripting language and
> functions are powerful enough to do that.
> If you are interested look at http://www.sun.com/bigadmin/content/
> There is an outline about how to add probes to an application here:
> Here is a little bit about providers and naming the probes: http://
> Here's an article: http://www.devx.com/Java/Article/33943 (trying
> google "DTrace Java examples")
> Here's more DTrace bloggyness at the 'Dtrace Three': http://
> blogs.sun.com/ahl/ http://blogs.sun.com/bmc/ http://blogs.sun.com/mws/
> I believe there is work on Ruby, Perl and Python DTrace providers too.
> Why an Erlang DTrace provider?
> So I hear you ask, why build a DTrace provider for erl when DTrace
> already works (on Solaris and Leopard) with erl?
> Well, DTrace will show which functions are called in the erl program
> (and which file descriptors and sockets are used, etc.), but will
> *not* show you the Erlang program events directly.
> Java 6 implement a DTrace provider, which surfaces Java method calls,
> class loading/unloading, the garbage collector, concurrency monitors
> etc. (rather than the details of the JVM, which are available anyway).
> So, I am suggesting an erl DTrace provider would show similar things,
> - module loading/unloading,
> - function calls (and maybe exits),
> - garbage collection events,
> - Erlang-process state/context-switching,
> - message send/receive.
> This would likely be sufficient for most purposes when combined with
> the existing DTrace support for tracing TCP and UDP sockets, file
> access etc from the erl process. Mac OS X 'Leopard' comes with a
> fancy GUI to show DTrace events, so that would give something like
> the new Percept but for many different types of event, not just
> process state.
> If I were building a large, complex system, availability of DTrace
> would be an important consideration. I believe several companies
> claim they moved to Solaris to get DTrace, and having used it for
> simple debugging and tuning, I can believe that.
> DTrace is so useful, that the erl developers and maintainers may find
> it extremely useful for debugging, testing, and tuning Erlang itself.
> Could I raise it as an EEP, or is it already on the TODO list?
> erlang-questions mailing list
Jan Henry Nystrom <jan@REDACTED>
Training & Research Manager @ Erlang Training and Consulting Ltd
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