Lisk-sdk: Investigate maxRelays and broadcastLimit numbers

[MaciejBaj]

Parent #2080

[4miners]

@MaciejBaj Are you sure that adjusting those params is a proper way to fix our current issues? It works fine on 0.9.x.

[MaciejBaj]

@4miners the P2P protocol is not compatible with 0.9.x - there is a difference between how the headers are being propagated. It's worth to simulate what's the ratio of reached peers during broadcasts while adjusting maxRelays and broadcastLimit parameters.

[nazarhussain]

@SargeKhan @MaciejBaj @4miners Here is the results of the combinations of different values in an emulated environment.

• Each series shows the increase in relay limit
• X-Axis shows the increase in broadcast limit.
• Y-Axis shows the percentage of network which missed the blocks
• Diagram is based on network of 250 peers
• Only one forging node (means broadcast initiated always from same peer)

[4miners]

@MaciejBaj Max relays and broadcast are for blocks, have nothing to do with headers.

@nazarhussain Very nice graph, thanks for the effort to create it. So looks like with current settings (relay: 2, broadcast: 20) more than 1/3 of the network should never get a block? Can you create another graph using 0.9.x version to compare the behavior?

[MaciejBaj]

@MaciejBaj Max relays and broadcast are for blocks, have nothing to do with headers.

That's correct, never suggested it does. The tests prepared by @nazarhussain are based on the dedicated script that simulates the network behaviour, not on the real network.

[nazarhussain]

The above graph was generated from am emulated environment which was completely synchronous. I converted it to asynchronous and broadcast in non-blocking mode. And here I get the result.

Based on this diagram we can see around 25% of the network missed the broadcast on 25 broadcast limit and 2 relay limit.

I suggest to change these values to either (40, 2) or (20, 3) for 250 node network.

And for 500 node network, value of (25, 3) or (75, 2) seems reasonable.

[nazarhussain]

@4miners @MaciejBaj Values of MaxRelays and Broadcast Limit is also related to broadcasting transactions not just the blocks.

[MaciejBaj]

Closes #2078, #2076, #2073.