[erlang-questions] what does suspend do ?

Dmitry Kolesnikov <>
Mon Feb 3 09:45:26 CET 2014


Hello,

This is suspension for garbage collection.

- Dmitry

On 02 Feb 2014, at 23:38, Philip Clarke <> wrote:

> Hi,
> 
> I have been doing some profiling using fprof on my system.
> Using fprof I see that ets:select is calling suspend.
> 
> I suspect that I have found a bottleneck where I have an ets table with write_concurrency defined and there are lots of processes doing reads thousands of times per second.  But my question is more general to profiling.
> 
> What exactly does suspend do ?  I suspect it may be an indication that my process has run out of reductions and is preempted by the scheduler ?
> Could anyone confirm please ?
> 
> Just in case it is useful, here is the relevant part of my fprof analysis file.
> 
> {[{{mymodule,get_values,1},           6, 2992.735,   31.313}],
>  { {ets,select,2},                                6, 2992.735,   31.313},     %
>  [{suspend,                                      92, 1707.908,    0.000},
>   {{lists,sum,1},                                 6, 1251.655,    0.709},
>   {garbage_collect,                               7,    1.859,    1.859}]}.
> 
> {[{{ets,select,2},                                6, 1251.655,    0.709}],
>  { {lists,sum,1},                                 6, 1251.655,    0.709},     %
>  [{{lists,sum,2},                                 6, 1250.946,    0.047}]}.
> 
> {[{{lists,sum,1},                                 6, 1250.946,    0.047},
>   {{lists,sum,2},                              20647,    0.000, 1241.206}],
>  { {lists,sum,2},                              20653, 1250.946, 1241.253},     %
>  [{suspend,                                      10,    9.693,    0.000},
>   {{lists,sum,2},                              20647,    0.000, 1241.206}]}.
> 
> Thanks
> Philip
> 
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> 
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