[erlang-questions] ETS and CPU
Tue Mar 15 12:32:24 CET 2016
Each successful ets:lookup call is a copy operation of the entire term
from ETS to the process heap.
If you are comparing ets:lookup of big map
to sending big map in message then I would expect
ets:lookup to win, as copy_shallow (used by ets:lookup)
is optimized to be faster than copy_struct (used by send).
On 03/15/2016 09:52 AM, Alex Howle wrote:
> I've been experiencing an issue and was wondering if anyone else has
> any experience in this area. I've stripped back the problem to its
> bare bones for the purposes of this mail.
> I have an Erlang 18.1 application that uses ETS to store an Erlang map
> structure. Using erts_debug:flat_size/1 I can approximate the map's
> size to be 1MB. Upon the necessary activity trigger the application
> spawns about 25 short-lived processes to perform the main work of the
> application. This activity trigger is fired roughly 9 times a second
> under normal operating conditions. Each of these 25 processes performs
> 1 x ets:lookup/2 calls to read from the map.
> What I've found is that the above implementation has a CPU profile
> that is quite "expensive" - each of the CPU cores (40 total comprised
> of 2 Processors with 10 hyperthreaded cores) frequently runs at 100%.
> The machine in question also has 32GB RAM of which about 9GB is used
> at peak. There is no swap usage whatsoever. Examination shows that
> copy_shallow is performing the most work.
> After changing the implementation so that the 25 spawned processes no
> longer read from the ETS table to retrieve the map structure and,
> instead the map is passed to the processes on spawn, the CPU usage on
> the server is considerably lower.
> Can anyone offer advice as to why I'm seeing the differing CPU profiles?
> erlang-questions mailing list
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