[erlang-questions] Relationship between erlang:memory/1, ets:info/2 and erlang:process_info/2

Simon MacMullen simon@REDACTED
Fri Sep 21 18:50:53 CEST 2012

I'm trying to write something that will account for memory use on a 
RabbitMQ system. To do this I'm trying to match up the numbers I get out 
of erlang:memory(ets) and ets:info(T, memory), and 
erlang:memory(processes) and erlang:process_info/2.

And it doesn't make a huge amount of sense to me. I don't expect things 
to match up perfectly, of course there will be some memory unaccounted 
for, but the ETS numbers in particular can be quite off:

1> erlang:memory(ets).

2> lists:sum([ets:info(T, memory) || T <- ets:all()]) * 

So I have ~2GB of ETS memory, and ~230MB unaccounted for. Should I 
expect these to match up closer?

And then...

3> erlang:memory(processes).

4> lists:sum([element(2, process_info(P, memory)) || P <- processes()]). 


So for processes there is less in total than if you add them all up. Is 
some memory shared? (Are we counting binaries and atoms in there as well?)

Is there a way to get this sort of information in a more consistent manner?

Cheers, Simon

Simon MacMullen
RabbitMQ, VMware

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