In the functional test wallet_groups.py we whitelist peers on all nodes (-whitelist=noban@127.0.0.1) to enable immediate tx relay for fast mempool synchronization. However, considering that this setting only applies to inbound peers and the default test topology looks like this:
0 node0 <--- node1 <---- node2 <--- ... <-- nodeN
txs propagate fast only from lower- to higher-numbered nodes (i.e. “left to right” in the above diagram) and take long from higher- to lower-numbered nodes (“right to left”) since in the latter direction we only have outbound peers, where the trickle relay is still active. As a consequence, if a tx is submitted from any node other than node0, the mempool synchronization can take quite long.
This PR fixes this by simply adding another connection from node0 to the last node, leading to a ~2-3x speedup (5 runs measured via time ./test/functional/wallet_groups.py are shown):
0master:
1 0m53.31s real 0m08.22s user 0m05.60s system
2 0m32.85s real 0m07.44s user 0m04.08s system
3 0m46.40s real 0m09.18s user 0m04.23s system
4 0m46.96s real 0m11.10s user 0m05.74s system
5 0m57.23s real 0m10.53s user 0m05.59s system
6
7PR:
8 0m19.64s real 0m09.58s user 0m05.50s system
9 0m18.05s real 0m07.77s user 0m04.03s system
10 0m18.99s real 0m07.90s user 0m04.25s system
11 0m17.49s real 0m07.56s user 0m03.92s system
12 0m18.11s real 0m07.74s user 0m03.88s system
Note that in most tests this is not a problem since txs very often originate from node0.
