make MAX_VOTERS and MAX_CANDIDATES in elections-phragmen configurable. …

…Fix: #11092 (#11908)

* make MAX_VOTERS and MAX_CANDIDATES in elections-phragmen configurable

* Configure election-phragmen in node bin configuring max candidates & voters

* Add document comment for added Config parameter

* Incorporate suggestion

* fix benchmarks

* Update frame/elections-phragmen/src/lib.rs

* Update frame/elections-phragmen/src/lib.rs

* fix wrong values

* fix typo

* docs

* more detailed docs

* fmt

* ".git/.scripts/bench-bot.sh" pallet dev pallet_elections_phragmen

Co-authored-by: Szegoo <[email protected]>
Co-authored-by: Sergej Sakac <[email protected]>
Co-authored-by: command-bot <>

bin/node/runtime/src/lib.rs

@@ -966,6 +966,8 @@ parameter_types! {
 	pub const TermDuration: BlockNumber = 7 * DAYS;
 	pub const DesiredMembers: u32 = 13;
 	pub const DesiredRunnersUp: u32 = 7;
+	pub const MaxVoters: u32 = 10 * 1000;
+	pub const MaxCandidates: u32 = 1000;
 	pub const ElectionsPhragmenPalletId: LockIdentifier = *b"phrelect";
 }
 
@@ -989,6 +991,8 @@ impl pallet_elections_phragmen::Config for Runtime {
 	type DesiredMembers = DesiredMembers;
 	type DesiredRunnersUp = DesiredRunnersUp;
 	type TermDuration = TermDuration;
+	type MaxVoters = MaxVoters;
+	type MaxCandidates = MaxCandidates;
 	type WeightInfo = pallet_elections_phragmen::weights::SubstrateWeight<Runtime>;
 }
 

frame/elections-phragmen/src/benchmarking.rs

@@ -36,7 +36,7 @@ fn endowed_account<T: Config>(name: &'static str, index: u32) -> T::AccountId {
 	let account: T::AccountId = account(name, index, 0);
 	// Fund each account with at-least his stake but still a sane amount as to not mess up
 	// the vote calculation.
-	let amount = default_stake::<T>(MAX_VOTERS) * BalanceOf::<T>::from(BALANCE_FACTOR);
+	let amount = default_stake::<T>(T::MaxVoters::get()) * BalanceOf::<T>::from(BALANCE_FACTOR);
 	let _ = T::Currency::make_free_balance_be(&account, amount);
 	// important to increase the total issuance since T::CurrencyToVote will need it to be sane for
 	// phragmen to work.
@@ -230,7 +230,7 @@ benchmarks! {
 
 	submit_candidacy {
 		// number of already existing candidates.
-		let c in 1 .. MAX_CANDIDATES;
+		let c in 1 .. T::MaxCandidates::get();
 		// we fix the number of members to the number of desired members and runners-up. We'll be in
 		// this state almost always.
 		let m = T::DesiredMembers::get() + T::DesiredRunnersUp::get();
@@ -261,7 +261,7 @@ benchmarks! {
 		// this will check members, runners-up and candidate for removal. Members and runners-up are
 		// limited by the runtime bound, nonetheless we fill them by `m`.
 		// number of already existing candidates.
-		let c in 1 .. MAX_CANDIDATES;
+		let c in 1 .. T::MaxCandidates::get();
 		// we fix the number of members to the number of desired members and runners-up. We'll be in
 		// this state almost always.
 		let m = T::DesiredMembers::get() + T::DesiredRunnersUp::get();
@@ -362,14 +362,14 @@ benchmarks! {
 
 	clean_defunct_voters {
 		// total number of voters.
-		let v in (MAX_VOTERS / 2) .. MAX_VOTERS;
+		let v in (T::MaxVoters::get() / 2) .. T::MaxVoters::get();
 		// those that are defunct and need removal.
-		let d in 1 .. (MAX_VOTERS / 2);
+		let d in 1 .. (T::MaxVoters::get() / 2);
 
 		// remove any previous stuff.
 		clean::<T>();
 
-		let all_candidates = submit_candidates::<T>(MAX_CANDIDATES, "candidates")?;
+		let all_candidates = submit_candidates::<T>(T::MaxCandidates::get(), "candidates")?;
 		distribute_voters::<T>(all_candidates, v, MAXIMUM_VOTE)?;
 
 		// all candidates leave.
@@ -389,9 +389,9 @@ benchmarks! {
 		// members, this is hard-coded in the runtime and cannot be trivially changed at this stage.
 		// Yet, change the number of voters, candidates and edge per voter to see the impact. Note
 		// that we give all candidates a self vote to make sure they are all considered.
-		let c in 1 .. MAX_CANDIDATES;
-		let v in 1 .. MAX_VOTERS;
-		let e in MAX_VOTERS .. MAX_VOTERS * MAXIMUM_VOTE as u32;
+		let c in 1 .. T::MaxCandidates::get();
+		let v in 1 .. T::MaxVoters::get();
+		let e in (T::MaxVoters::get()) .. T::MaxVoters::get() as u32 * MAXIMUM_VOTE as u32;
 		clean::<T>();
 
 		// so we have a situation with v and e. we want e to basically always be in the range of `e
@@ -425,9 +425,9 @@ benchmarks! {
 
 	#[extra]
 	election_phragmen_c_e {
-		let c in 1 .. MAX_CANDIDATES;
-		let e in MAX_VOTERS .. MAX_VOTERS * MAXIMUM_VOTE as u32;
-		let fixed_v = MAX_VOTERS;
+		let c in 1 .. T::MaxCandidates::get();
+		let e in (T::MaxVoters::get()) .. T::MaxVoters::get() * MAXIMUM_VOTE as u32;
+		let fixed_v = T::MaxVoters::get();
 		clean::<T>();
 
 		let votes_per_voter = e / fixed_v;
@@ -459,7 +459,7 @@ benchmarks! {
 	#[extra]
 	election_phragmen_v {
 		let v in 4 .. 16;
-		let fixed_c = MAX_CANDIDATES / 10;
+		let fixed_c = T::MaxCandidates::get() / 10;
 		let fixed_e = 64;
 		clean::<T>();
 

frame/elections-phragmen/src/lib.rs

@@ -125,17 +125,6 @@ pub mod migrations;
 /// The maximum votes allowed per voter.
 pub const MAXIMUM_VOTE: usize = 16;
 
-// Some safe temp values to make the wasm execution sane while we still use this pallet.
-#[cfg(test)]
-pub(crate) const MAX_CANDIDATES: u32 = 100;
-#[cfg(not(test))]
-pub(crate) const MAX_CANDIDATES: u32 = 1000;
-
-#[cfg(test)]
-pub(crate) const MAX_VOTERS: u32 = 1000;
-#[cfg(not(test))]
-pub(crate) const MAX_VOTERS: u32 = 10 * 1000;
-
 type BalanceOf<T> =
 	<<T as Config>::Currency as Currency<<T as frame_system::Config>::AccountId>>::Balance;
 type NegativeImbalanceOf<T> = <<T as Config>::Currency as Currency<
@@ -259,6 +248,21 @@ pub mod pallet {
 		#[pallet::constant]
 		type TermDuration: Get<Self::BlockNumber>;
 
+		/// The maximum number of candidates in a phragmen election.
+		///
+		/// Warning: The election happens onchain, and this value will determine
+		/// the size of the election. When this limit is reached no more
+		/// candidates are accepted in the election.
+		#[pallet::constant]
+		type MaxCandidates: Get<u32>;
+
+		/// The maximum number of voters to allow in a phragmen election.
+		///
+		/// Warning: This impacts the size of the election which is run onchain.
+		/// When the limit is reached the new voters are ignored.
+		#[pallet::constant]
+		type MaxVoters: Get<u32>;
+
 		/// Weight information for extrinsics in this pallet.
 		type WeightInfo: WeightInfo;
 	}
@@ -397,7 +401,10 @@ pub mod pallet {
 
 			let actual_count = <Candidates<T>>::decode_len().unwrap_or(0) as u32;
 			ensure!(actual_count <= candidate_count, Error::<T>::InvalidWitnessData);
-			ensure!(actual_count <= MAX_CANDIDATES, Error::<T>::TooManyCandidates);
+			ensure!(
+				actual_count <= <T as Config>::MaxCandidates::get(),
+				Error::<T>::TooManyCandidates
+			);
 
 			let index = Self::is_candidate(&who).err().ok_or(Error::<T>::DuplicatedCandidate)?;
 
@@ -913,10 +920,11 @@ impl<T: Config> Pallet<T> {
 
 		let mut num_edges: u32 = 0;
 
+		let max_voters = <T as Config>::MaxVoters::get() as usize;
 		// used for prime election.
 		let mut voters_and_stakes = Vec::new();
 		match Voting::<T>::iter().try_for_each(|(voter, Voter { stake, votes, .. })| {
-			if voters_and_stakes.len() < MAX_VOTERS as usize {
+			if voters_and_stakes.len() < max_voters {
 				voters_and_stakes.push((voter, stake, votes));
 				Ok(())
 			} else {
@@ -930,7 +938,7 @@ impl<T: Config> Pallet<T> {
 					"Failed to run election. Number of voters exceeded",
 				);
 				Self::deposit_event(Event::ElectionError);
-				return T::DbWeight::get().reads(3 + MAX_VOTERS as u64)
+				return T::DbWeight::get().reads(3 + max_voters as u64)
 			},
 		}
 
@@ -1266,6 +1274,8 @@ mod tests {
 
 	parameter_types! {
 		pub const ElectionsPhragmenPalletId: LockIdentifier = *b"phrelect";
+		pub const PhragmenMaxVoters: u32 = 1000;
+		pub const PhragmenMaxCandidates: u32 = 100;
 	}
 
 	impl Config for Test {
@@ -1284,6 +1294,8 @@ mod tests {
 		type LoserCandidate = ();
 		type KickedMember = ();
 		type WeightInfo = ();
+		type MaxVoters = PhragmenMaxVoters;
+		type MaxCandidates = PhragmenMaxCandidates;
 	}
 
 	pub type Block = sp_runtime::generic::Block<Header, UncheckedExtrinsic>;