<div dir="ltr"><div><div>As others have said that this will copy the map from the spawner to the spawnee process. The interesting thing is what you do with afterwards. If you just carry it around as process local data then there is no extra copying except during GC which you can't do anything about. If, however, you then store the map as a map in an ETS table you will be copying the map between the process and the table for every access. This will be very inefficient if you just want to access one key in the map as you will first have to copy the whole map from the ETS table to the process, access the key, and then if you are writing to the map copy it all back to the ETS table. It would then be better to split the map into separate {Key,Value} tuples which you store as separate elements in the ETS table.<br><br></div>ETS tables are great but you have to be aware of the copying. Erlang doesn't do shared global data! ETS tables aren't shared, just globally accessible.<br><br></div>Robert<br><br></div><div class="gmail_extra"><br><div class="gmail_quote">On 15 March 2016 at 16:07, Alex Howle <span dir="ltr"><<a href="mailto:itshowlertime@gmail.com" target="_blank">itshowlertime@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">The map is not being sent as a message. It is passed in to the spawned processes by being in scope of the spawned function.</p>
<p dir="ltr">Pseudocode:</p>
<p dir="ltr">A=bigmap,<br>
spawn(fun()-> do_something(A) end).</p>
<div class="gmail_quote">On 15 Mar 2016 13:43, "Alex Howle" <<a href="mailto:itshowlertime@gmail.com" target="_blank">itshowlertime@gmail.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">The map is not being sent as a message. It is passed in to the spawned processes by being in scope of the spawned function.</p>
<p dir="ltr">Pseudocode:</p>
<p dir="ltr">A=bigmap,<br>
spawn(fun()-> do_something(A) end).</p><div><div class="h5">
<div class="gmail_quote">On 15 Mar 2016 11:32, "Sverker Eriksson" <<a href="mailto:sverker.eriksson@ericsson.com" target="_blank">sverker.eriksson@ericsson.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
Each successful ets:lookup call is a copy operation of the entire
term<br>
from ETS to the process heap.<br>
<br>
If you are comparing ets:lookup of big map<br>
to sending big map in message then I would expect<br>
ets:lookup to win, as copy_shallow (used by ets:lookup)<br>
is optimized to be faster than copy_struct (used by send).<br>
<br>
<br>
/Sverker, Erlang/OTP<br>
<br>
<br>
<div>On 03/15/2016 09:52 AM, Alex Howle
wrote:<br>
</div>
<blockquote type="cite">
<p dir="ltr">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.</p>
<p dir="ltr"> </p>
<p dir="ltr">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.</p>
<p dir="ltr"> </p>
<p dir="ltr">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.</p>
<p dir="ltr"> </p>
<p dir="ltr">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.<br>
</p>
<p dir="ltr"> </p>
<p dir="ltr">Can anyone offer advice as to why I'm seeing the
differing CPU profiles?<br>
</p>
<br>
<fieldset></fieldset>
<br>
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