[devel] Implement a crawling mechanism for our new bandwidth accounting mechanism

[devos50]

Now that #5626 has been merged, we require a mechanism for peers to construct the global work graph. Specifically, each peer should slowly explore the (latest) transactions of other peers, which acts as input for our upcoming reputation mechanism. #5626 does not implement the required primitives for requesting transactions from other peers. We also need this to deploy a crawler that monitors network health.

The approach

The mechanism relies on simple pull-based gossip. Peers send out TransactionQuery message to other peers of which it would like to request the latest, pairwise transactions. Peers send back individual Transaction messages. Queries do not have an associated request cache, to keep the mechanism simple. In fact, our mechanism can deal with missing messages or peers that go offline quickly after receiving a query.

For now, we will query the immediate neighbours in a round-robin fashion. We can later extend our approach to also query the transactions of two-hop/three-hop peers.

[drew2a]

@devos50 should we add this issue to 7.6.0 milestone?

[devos50]

Sure, we can do that 👍