[mqtt] Benchmark broker message dispatching

[dmolokanov]

In order to verify how quickly broker can dispatch messages we need some benchmark tests.
dispatch_message benches start broker with empty state and no network connections. Firstly, each bench test creates a given number of publishers, subscribers and connects them to a broker. Then it makes a series of exercises to send messages to a broker and measures the time between a message successfully sent to a broker and broker processed this message. For this case broker extended with a on_publish "callback" which has to be exposed only for benchmark tests.

Scenarios supported:

1-to-1

Each publisher sends messages to one corresponding subscriber:

pub1 pub topic/1            sub1 sub topic/1
pub2 pub topic/2            sub2 sub topic/2
pub2 pub topic/N            sub2 sub topic/N

fan-in

All publishers send message to a randomly chose topic

pub1 pub topic/2            sub1 sub topic/1
pub2 pub topic/2            sub2 sub topic/2
pubN pub topic/2            sub2 sub topic/N

fan-out

Multiple publishers sends messages to a topic all subscribers subscribed to

pub1 pub topic/foo            sub1 sub topic/foo
pub2 pub topic/foo            sub2 sub topic/foo
pubN pub topic/foo            sub2 sub topic/foo

How to run benches

cd mqtt 
cargo bench --bench dispatch_messages \
    --features="benches" \
    --manifest-path mqtt-broker/Cargo.toml

or

cd mqtt/mqtt-broker
cargo bench --bench dispatch_messages --features="benches"

to run all benches

cd mqtt/mqtt-broker
cargo bench --all --features="benches"

[vipeller]

these three methods look exactly the same, except the strategy they create and the name. Can it be made into a single method, and fan_in()/fan_out()/one_to_one() just call that single method with a "strategy creator" function injected?

[dmolokanov]

Yeah, I thought about that. I still wonder if number of publishers should not be equal number of subscribers. it may vary depending on strategy...

[vadim-kovalyov]

LGTM!

[vadim-kovalyov]

nit: log(...); break;

[dmolokanov]

it logged bellow