Cost analysis of a council election full block (#2782)

polkadot/runtime/polkadot/src/lib.rs

@@ -1549,6 +1549,39 @@ mod test_fees {
 		test_with_multiplier(Multiplier::saturating_from_rational(1, 1_000_000_000u128));
 	}
 
+	#[test]
+	fn full_block_council_election_cost() {
+		// the number of voters needed to consume almost a full block in council election, and how
+		// much it is going to cost.
+		use pallet_elections_phragmen::WeightInfo;
+
+		// Loser candidate lose a lot of money; sybil attack by candidates is even more expensive,
+		// and we don't care about it here. For now, we assume no extra candidates, and only
+		// superfluous voters.
+		let candidates = DesiredMembers::get() + DesiredRunnersUp::get();
+		let mut voters = 1u32;
+		let weight_with = |v| {
+			<Runtime as pallet_elections_phragmen::Config>::WeightInfo::election_phragmen(
+				candidates,
+				v,
+				v * 16,
+			)
+		};
+
+		while weight_with(voters) <= BlockWeights::get().max_block {
+			voters += 1;
+		}
+
+		let cost = voters as Balance * (VotingBondBase::get() + 16 * VotingBondFactor::get());
+		let cost_dollars = cost / DOLLARS;
+		println!(
+			"can support {} voters in a single block for council elections; total bond {}",
+			voters,
+			cost_dollars,
+		);
+		assert!(cost_dollars > 150_000); // DOLLAR ~ new DOT ~ 10e10
+	}
+
 	#[test]
 	fn nominator_limit() {
 		use pallet_election_provider_multi_phase::WeightInfo;