[erlang-questions] Process heap inspector
Björn-Egil Dahlberg
egil@REDACTED
Mon Nov 28 15:47:29 CET 2011
On 2011-11-28 14:25, Michal Ptaszek wrote:
> So there is a chance to get it into official Erlang/OTP release? :)
I would say there is a chance ... a small one perhaps. =)
I agree with Kostis. It can be a very handy tool to inspect data in a
process heap. At OTP (erts-team) we use gdb with plugins to inspect
erlang process heaps when something goes horribly wrong. So it can be
very useful.
I am not sure I would allow it in a production beam. If I had my way I
would remove all tracing as well and only have it in a instrumented
beam. I've seen production code use tracing to all sorts of interesting
stuff. Bad practice (tm). It is too powerful.
(That said, I wouldn't really like to debug a live system without those
tools)
I don't have a decisive opinion atm.
// Björn-Egil
>
> On Nov 28, 2011, at 2:05 PM, Björn-Egil Dahlberg wrote:
>
>> On 2011-11-28 12:11, Ahmed Omar wrote:
>>> I like the idea but i'm HORRIFIED about people misusing that and
>>> actually try to read internal states within their programs :D
>>
>> I would put such a function in erts_debug:inspect_heap/1 instead.
>>
>> // Björn-Egil
>>
>>
>>>
>>> On Mon, Nov 28, 2011 at 12:02 PM, Michal Ptaszek
>>> <michal.ptaszek@REDACTED
>>> <mailto:michal.ptaszek@REDACTED>> wrote:
>>>
>>> Hey,
>>>
>>> good point, I knew I forgot about something - will add support
>>> for that
>>> really soon.
>>>
>>> Kind regards,
>>> Michal Ptaszek
>>>
>>> On Nov 28, 2011, at 11:02 AM, Attila Rajmund Nohl wrote:
>>>
>>> > Hello!
>>> >
>>> > I really like the idea. But shouldn't this list include the
>>> message queue too?
>>> >
>>> > 2011/11/28 Michal Ptaszek <michal.ptaszek@REDACTED
>>> <mailto:michal.ptaszek@REDACTED>>:
>>> >> Hi everyone,
>>> >>
>>> >> This idea was born in my mind when debugging some complex,
>>> live system
>>> >> and trying to figure out where did all my memory go.
>>> >>
>>> >> So, when debugging live system/investigating suspicious
>>> memory consumption patterns
>>> >> or simply trying to understand better what's going on with
>>> our processes, it might be useful
>>> >> to take a peep at the data given process operates on.
>>> >>
>>> >> Right now it is possible to fetch internal gen_* processes
>>> state via sys:get_status, we can do
>>> >> some tracing (even using DTrace), we can also check
>>> erlang:process_info output and analyze
>>> >> it to become more or less familiar with what is the heap size
>>> of our suspect. Still, not all processes
>>> >> are OTP-compatible, and even if: we are going to get only
>>> "alive" data coming from process' state
>>> >> (not counting the outdated, not yet garbage collected terms).
>>> Also, process_info informs us only
>>> >> about allocated size of the heap, not about the actual usage
>>> (although the pre-allocated chunks
>>> >> are not available to the system, yet we might see how far we
>>> are from growing/shrinking it).
>>> >>
>>> >> Enough with introduction, let's focus on the actual meat: my
>>> idea was to create a new BIF,
>>> >> namely erlang:inspect_heap(Pid) that allows us to take a look
>>> at any process' heap, fetch the
>>> >> terms residing there and check their actual size. So, for
>>> instance:
>>> >>
>>> >>> (ejabberd@REDACTED)12> S = erlang:inspect_heap(pid(0, 358, 0)).
>>> >>> [{[[<<"5">>]|
>>> >>>
>>> 284735200226724471091958640173737944785062822211005333957298336375301959844499896296764925551414319236776784],
>>> >>> 20},
>>> >>> {{'$internal_queue_len',0},3},
>>> >>> {{random_seed,{8236,26623,17360}},7},
>>> >>> {{'$ancestors',[ejabberd_c2s_sup,ejabberd_sup,<0.40.0>]},9},
>>> >>> {{'$initial_call',{gen,init_it,6}},7},
>>> >>> {{state,{socket_state,tls,
>>> >>> {tlssock,#Port<0.3936>,#Port<0.3938>},
>>> >>> <0.357.0>},
>>> >>>
>>> ejabberd_socket,#Ref<0.0.0.10120>,false,<<"2855118401">>,
>>> >>> {sasl_state,"jabber",<<"pvp.net
>>> <http://pvp.net/>">>,[],
>>> >>>
>>> #Fun<ejabberd_c2s.0.67315917>,#Fun<ejabberd_c2s.1.67315917>,
>>> >>>
>>> #Fun<ejabberd_c2s.2.67315917>,cyrsasl_digest,
>>> >>> {state,5,<<"3598825873">>,
>>> >>> {<<"dupa">>,<<...>>},
>>> >>> <<>>,#Fun<ejabberd_c2s.0.67315917>,...}},
>>> >>> true,
>>> >>> {jid,<<"dupa">>,<<"pvp.net
>>> <http://pvp.net/>">>,<<"hubbard">>,<<"dupa">>,
>>> >>> <<"pvp.net <http://pvp.net/>">>,<<"hubbard">>},
>>> >>> <<"Nicknamedupa">>,
>>> >>> {{1322,217197,749816},<0.358.0>},
>>> >>> {1,{<<"dupa">>,nil,nil}},
>>> >>> {1,{<<"dupa">>,nil,nil}},
>>> >>> {1,{<<"dupa">>,nil,nil}},
>>> >>> {xmlelement,<<"presence">>,[],
>>> >>>
>>> [{xmlcdata,<<...>>},{xmlelement,...},{...}|...]},
>>> >>> {userlist,none,[],false}},
>>> >>> 564},
>>> >>> {{limits,undefined},3},
>>> >>> {{[],[]},3}]
>>> >>
>>> >> gives us a pretty good knowledge on <0.358.0>:
>>> >> • '$_' - OTP + gen_fsm2 process dictionary stuff, 3, 9, 7
>>> words each
>>> >> • random_seed - obvious
>>> >> • {{limits,undefined},3} - internal limits for gen_fsm2
>>> message queue, 3 words
>>> >> • {[], []} - most probably leftovers after fetching user's
>>> presence lists
>>> >> • {state, _} - gen_fsm2 state record - 564 words
>>> >> • {[[<<"5">>]|, ...} - sequential tracing tokens? (I'm not
>>> very familiar with that, I would
>>> >> say that's something from our rootset
>>> >>
>>> >> The implementation is rather simple: if the process we probe
>>> is not the caller one (we are not doing
>>> >> erlang:inspect_heap(self()), the data is copied from the
>>> callee heap to caller heap (to prevent from having
>>> >> cross-process references in variables), then we compute flat
>>> size of the each term we moved. Also, rootset
>>> >> is also included in the summary (i.e. process dict, seq
>>> tokens, etc.).
>>> >>
>>> >> Code is included in my inspect_heap OTP branch on:
>>> >> github: https://github.com/paulgray/otp/tree/inspect_heap
>>> >>
>>> >> I am still a little bit hesitant about suspending process we
>>> probe: can anyone tell
>>> >> me if acquiring main process lock would be enough to keep its
>>> heap untouched during
>>> >> the call?
>>> >>
>>> >> Please, do point any bugs and tell me what do you think about
>>> the idea.
>>> >>
>>> >> Best regards,
>>> >> Michal Ptaszek
>>> >> _______________________________________________
>>> >> erlang-questions mailing list
>>> >> erlang-questions@REDACTED <mailto:erlang-questions@REDACTED>
>>> >> http://erlang.org/mailman/listinfo/erlang-questions
>>> >>
>>>
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>>>
>>>
>>>
>>>
>>> --
>>> Best Regards,
>>> - Ahmed Omar
>>> http://nl.linkedin.com/in/adiaa
>>> Follow me on twitter
>>> @spawn_think <http://twitter.com/#%21/spawn_think>
>>>
>>>
>>>
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>>
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