[erlang-questions] Discussion and proposal regarding rpc scalability

Sean Cribbs <>
Thu Feb 11 22:58:21 CET 2016


José,

It's interesting to me that your example of making registered RPC receivers
isn't that much different from having registered processes with specific
messages (call/cast/etc) they handle. What do you see as the use-case of
allowing generic RPC in that scenario?

Cheers,

Sean

On Thu, Feb 11, 2016 at 3:04 PM, José Valim <
> wrote:

> Hello everyone,
>
> I was reading the publication "Investigating the Scalability Limits of
> Distributed Erlang
> <http://www.dcs.gla.ac.uk/~amirg/publications/DE-Bench.pdf>" and one of
> the conclusions is:
>
> *> We observed that distributed Erlang scales linearly up to 150 nodes
> when no global command is made. Our results reveal that the latency of rpc
> calls rises as cluster size grows. This shows that spawn scales much better
> than rpc and using spawn instead of rpc in the sake of scalability is
> advised. *
>
> The reason why is highlighted in a previous section:
>
> *> To find out why rpc’s latency increases as the cluster size grows, we
> need to know more about rpc. (...) There is a generic server process (gen
> server) on each Erlang node which is named rex. This process is responsible
> for receiving and handling all rpc requests that come to an Erlang node.
> After handling the request, generated results will be returned to the
> source node. In addition to user applications, rpc is also used by many
> built-in OTP modules, and so it can be overloaded as a shared service.*
>
> In other words, the more applications we have relying on rpc, the more
> likely rpc will become a bottleneck and increase latency. I believe we have
> three options here:
>
> 1. Promote spawn over rpc, as the paper conclusion did (i.e. mention spawn
> in the rpc docs and so on)
> 2. Leave things as is
> 3. Allow "more scalable" usage of rpc by supporting application specific
> rpc instances
>
> In particular, my proposal for 3 is to allow developers to spawn their own
> rpc processes. In other words, we can expose:
>
> rpc:start_link(my_app_rpc) %% start your own rpc
>
> rpc:call({my_app_rpc, nodename}, foo, bar, [1, 2, 3]) %% invoke your own
> rpc at the given node
>
>
> This is a very simple solution that moves the bottleneck away from rpc's
> rex process since developers can place their own rpc processes in their
> application's tree. The code changes required to support this feature are
> also minimal and are almost all at the API level, i.e. support a tuple were
> today a node is expected or allow the name as argument, mimicking the same
> API provided by gen_server that rpc relies on. We won't change
> implementation details. Finally, I believe it will provide a more
> predictable usage of rpc.
>
> Feedback is appreciated!
>
> *José Valim*
> www.plataformatec.com.br
> Skype: jv.ptec
> Founder and Director of R&D
>
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> 
> http://erlang.org/mailman/listinfo/erlang-questions
>
>
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