When transaction spreads through the network many nodes are likely to get it
in roughly the same time. They will rebroadcast it also in roughly the same
time. As we have a number of peers it's quite likely that we'd get an Inv with
the same transaction from multiple peers simultaneously. We will ask them for
this transaction (independently!) and again we're likely to get it in roughly
the same time. So we can easily end up with multiple threads processing the
same transaction. Only one will succeed, but we can actually easily avoid
doing it in the first place saving some CPU cycles for other things.
Notice that we can't do it _before_ receiving a transaction because nothing
guarantees that the peer will respond to our transaction request, so
communication overhead is unavoidable at the moment, but saving on processing
already gives quite interesting results.
Baseline, four nodes with 10 workers:
RPS 7176.784 7014.511 6139.663 7191.280 7080.852 ≈ 6921 ± 5.72%
TPS 6945.409 6562.756 5927.050 6681.187 6821.794 ≈ 6588 ± 5.38%
CPU % 44.400 43.842 40.418 49.211 49.370 ≈ 45.4 ± 7.53%
Mem MB 2693.414 2640.602 2472.007 2731.482 2707.879 ≈ 2649 ± 3.53%
Patched:
RPS ≈ 7791.675 7996.559 7834.504 7746.705 7891.614 ≈ 7852 ± 1.10% ↑ 13.45%
TPS ≈ 7241.497 7711.765 7520.211 7425.890 7334.443 ≈ 7447 ± 2.17% ↑ 13.04%
CPU % 29.853 39.936 39.945 36.371 39.999 ≈ 37.2 ± 10.57% ↓ 18.06%
Mem MB 2749.635 2791.609 2828.610 2910.431 2863.344 ≈ 2829 ± 1.97% ↑ 6.80%
Most of the time on healthy network we see new transactions appearing that are
not present in the mempool. Once they get into mempool we don't ask for them
again when some other peer sends an Inv with them. Then these transactions are
usually added into block, removed from mempool and no one actually sends them
again to us. Some stale nodes can do that, but it's not very likely to
happen.
At the receiving end at the same time it's quite expensive to do full chain
HasTransaction() query, so if we can avoid doing that it's always good. Here
it technically allows resending old transaction that will be re-requested and
an attempt to add it to mempool will be made. But it'll inevitably fail
because the same HasTransaction() check is done there too. One can try to
maliciously flood the node with stale transactions but it doesn't differ from
flooding it with any other invalid transactions, so there is no new attack
vector added.
Baseline, 4 nodes with 10 workers:
RPS 6902.296 6465.662 6856.044 6785.515 6157.024 ≈ 6633 ± 4.26%
TPS 6468.431 6218.867 6610.565 6288.596 5790.556 ≈ 6275 ± 4.44%
CPU % 50.231 42.925 49.481 48.396 42.662 ≈ 46.7 ± 7.01%
Mem MB 2856.841 2684.103 2756.195 2733.485 2422.787 ≈ 2691 ± 5.40%
Patched:
RPS 7176.784 7014.511 6139.663 7191.280 7080.852 ≈ 6921 ± 5.72% ↑ 4.34%
TPS 6945.409 6562.756 5927.050 6681.187 6821.794 ≈ 6588 ± 5.38% ↑ 4.99%
CPU % 44.400 43.842 40.418 49.211 49.370 ≈ 45.4 ± 7.53% ↓ 2.78%
Mem MB 2693.414 2640.602 2472.007 2731.482 2707.879 ≈ 2649 ± 3.53% ↓ 1.56%
Network communication takes time. Handling some messages (like transaction)
also takes time. We can share this time by making handler a separate
goroutine. So while message is being handled receiver can already get and
parse the next one.
It doesn't improve metrics a lot, but still I think it makes sense and in some
scenarios this can be more beneficial than this.
e41fc2fd1b, 4 nodes, 10 workers
RPS 6732.979 6396.160 6759.624 6246.398 6589.841 ≈ 6545 ± 3.02%
TPS 6491.062 5984.190 6275.652 5867.477 6360.797 ≈ 6196 ± 3.77%
CPU % 42.053 43.515 44.768 40.344 44.112 ≈ 43.0 ± 3.69%
Mem MB 2564.130 2744.236 2636.267 2589.505 2765.926 ≈ 2660 ± 3.06%
Patched:
RPS 6902.296 6465.662 6856.044 6785.515 6157.024 ≈ 6633 ± 4.26% ↑ 1.34%
TPS 6468.431 6218.867 6610.565 6288.596 5790.556 ≈ 6275 ± 4.44% ↑ 1.28%
CPU % 50.231 42.925 49.481 48.396 42.662 ≈ 46.7 ± 7.01% ↑ 8.60%
Mem MB 2856.841 2684.103 2756.195 2733.485 2422.787 ≈ 2691 ± 5.40% ↑ 1.17%
Asynchronous tryAddress() routines may get dial result AFTER the switch to
another test, so we need to ensure that they'll get the result intended for
this particular call. Fixes:
2021-07-07T20:25:40.1624521Z === RUN TestDefaultDiscoverer
2021-07-07T20:25:40.1625316Z discovery_test.go:159: timeout expecting for transport dial; i: 2, j: 1
2021-07-07T20:25:40.1626319Z --- FAIL: TestDefaultDiscoverer (1.19s)
We don't care much about dialing, but the same constant is used in outer
discoverer loop in case no connections are established and we have no
connections established.
It's only used to sign/verify it and is not a part of the structure. It's
still neded in consensus.Payload though because that's the way dbft library
is.
It's not network-tied any more, network is only needed to
sign/verify. Unfortunately we still have to keep network in consensus data
structures because of dbft library interface.
