Understanding concurrent connections and event groups

[Jack-Terranova-Imprivata]

Hello,

The documentation seems to make a clear recommendation regarding connection/loop config: "As a rule of thumb, Pushy is most efficient in terms of processing time when it has one or two threads per CPU core and one or two connections per thread, not to exceed more than two connections per server. Still, lots of factors can limit overall performance:"

But when you say "not to exceed more than two connections per server" did you really mean "server"? Does that mean if I deploy an app to a machine and configure a Pushy client, then it should not have more than 2 concurrent connections configured regardless of the cores on the machine?

And, also, the Javadoc for setEventLoopGroup states "Generally speaking, callers don't need to set event loop groups for clients, but it may be useful to specify an event loop group under certain circumstances" (like sharing a group across clients)

So, for example, If I specify 2 connections, will Pushy match that config with a 2-thread event loop group? Or do I need to specify the 2-thread group myself if I really want a 1/1 connection/group ratio?

Thanks!

[jchambers]

But when you say "not to exceed more than two connections per server" did you really mean "server"? Does that mean if I deploy an app to a machine and configure a Pushy client, then it should not have more than 2 concurrent connections configured regardless of the cores on the machine?

No. I'll clarify this in the docs, but that means more than two concurrent connections per APNs server. You can get an idea of how many servers Apple has in play using dig:

❯ dig +short api.push.apple.com
api-vs.push-apple.com.akadns.net.
17.188.182.11
17.188.180.14
17.188.180.78
17.188.180.201
17.188.181.73
17.188.181.202
17.188.182.138
17.188.180.202

In this case, we see that Apple is advertising 8 distinct APNs servers, and we'll probably see diminishing returns on additional connections beyond ~16.

So, for example, If I specify 2 connections, will Pushy match that config with a 2-thread event loop group? Or do I need to specify the 2-thread group myself if I really want a 1/1 connection/group ratio?

Please see the ApnsClient docs (emphasis added):

Clients are constructed using an ApnsClientBuilder. Callers may optionally specify an EventLoopGroup when constructing a new client. If no event loop group is specified, clients will create and manage their own single-thread event loop group.

So, yes, if you want more than one thread, you'll need to provide your own event loop group.