v2.1: add fanout to tpu-client-next (backport of #3478)

Cargo.toml

@@ -513,6 +513,7 @@ solana-test-validator = { path = "test-validator", version = "=2.1.2" }
 solana-thin-client = { path = "thin-client", version = "=2.1.2" }
 solana-transaction-error = { path = "sdk/transaction-error", version = "=2.1.2" }
 solana-tpu-client = { path = "tpu-client", version = "=2.1.2", default-features = false }
+solana-tpu-client-next = { path = "tpu-client-next", version = "=2.1.2" }
 solana-transaction-status = { path = "transaction-status", version = "=2.1.2" }
 solana-transaction-status-client-types = { path = "transaction-status-client-types", version = "=2.1.2" }
 solana-transaction-metrics-tracker = { path = "transaction-metrics-tracker", version = "=2.1.2" }

tpu-client-next/src/connection_worker.rs

@@ -14,7 +14,10 @@ use {
         clock::{DEFAULT_MS_PER_SLOT, MAX_PROCESSING_AGE, NUM_CONSECUTIVE_LEADER_SLOTS},
         timing::timestamp,
     },
-    std::net::SocketAddr,
+    std::{
+        net::SocketAddr,
+        sync::{atomic::Ordering, Arc},
+    },
     tokio::{
         sync::mpsc,
         time::{sleep, Duration},
@@ -72,7 +75,7 @@ pub(crate) struct ConnectionWorker {
     connection: ConnectionState,
     skip_check_transaction_age: bool,
     max_reconnect_attempts: usize,
-    send_txs_stats: SendTransactionStats,
+    send_txs_stats: Arc<SendTransactionStats>,
     cancel: CancellationToken,
 }
 
@@ -93,6 +96,7 @@ impl ConnectionWorker {
         transactions_receiver: mpsc::Receiver<TransactionBatch>,
         skip_check_transaction_age: bool,
         max_reconnect_attempts: usize,
+        send_txs_stats: Arc<SendTransactionStats>,
     ) -> (Self, CancellationToken) {
         let cancel = CancellationToken::new();
 
@@ -103,7 +107,7 @@ impl ConnectionWorker {
             connection: ConnectionState::NotSetup,
             skip_check_transaction_age,
             max_reconnect_attempts,
-            send_txs_stats: SendTransactionStats::default(),
+            send_txs_stats,
             cancel: cancel.clone(),
         };
 
@@ -155,11 +159,6 @@ impl ConnectionWorker {
         }
     }
 
-    /// Retrieves the statistics for transactions sent by this worker.
-    pub fn transaction_stats(&self) -> &SendTransactionStats {
-        &self.send_txs_stats
-    }
-
     /// Sends a batch of transactions using the provided `connection`.
     ///
     /// Each transaction in the batch is sent over the QUIC streams one at the
@@ -183,11 +182,12 @@ impl ConnectionWorker {
 
             if let Err(error) = result {
                 trace!("Failed to send transaction over stream with error: {error}.");
-                record_error(error, &mut self.send_txs_stats);
+                record_error(error, &self.send_txs_stats);
                 self.connection = ConnectionState::Retry(0);
             } else {
-                self.send_txs_stats.successfully_sent =
-                    self.send_txs_stats.successfully_sent.saturating_add(1);
+                self.send_txs_stats
+                    .successfully_sent
+                    .fetch_add(1, Ordering::Relaxed);
             }
         }
         measure_send.stop();
@@ -221,14 +221,14 @@ impl ConnectionWorker {
                     }
                     Err(err) => {
                         warn!("Connection error {}: {}", self.peer, err);
-                        record_error(err.into(), &mut self.send_txs_stats);
+                        record_error(err.into(), &self.send_txs_stats);
                         self.connection =
                             ConnectionState::Retry(max_retries_attempt.saturating_add(1));
                     }
                 }
             }
             Err(connecting_error) => {
-                record_error(connecting_error.clone().into(), &mut self.send_txs_stats);
+                record_error(connecting_error.clone().into(), &self.send_txs_stats);
                 match connecting_error {
                     ConnectError::EndpointStopping => {
                         debug!("Endpoint stopping, exit connection worker.");

tpu-client-next/src/connection_workers_scheduler.rs

@@ -9,7 +9,8 @@ use {
             create_client_config, create_client_endpoint, QuicClientCertificate, QuicError,
         },
         transaction_batch::TransactionBatch,
-        workers_cache::{WorkerInfo, WorkersCache, WorkersCacheError},
+        workers_cache::{maybe_shutdown_worker, WorkerInfo, WorkersCache, WorkersCacheError},
+        SendTransactionStats,
     },
     log::*,
     quinn::Endpoint,
@@ -39,6 +40,25 @@ pub enum ConnectionWorkersSchedulerError {
     LeaderReceiverDropped,
 }
 
+/// [`Fanout`] is a configuration struct that specifies how many leaders should
+/// be targeted when sending transactions and connecting.
+///
+/// Note, that the unit is number of leaders per
+/// [`NUM_CONSECUTIVE_LEADER_SLOTS`]. It means that if the leader schedule is
+/// [L1, L1, L1, L1, L1, L1, L1, L1, L2, L2, L2, L2], the leaders per
+/// consecutive leader slots are [L1, L1, L2], so there are 3 of them.
+///
+/// The idea of having a separate `connect` parameter is to create a set of
+/// nodes to connect to in advance in order to hide the latency of opening new
+/// connection. Hence, `connect` must be greater or equal to `send`
+pub struct Fanout {
+    /// The number of leaders to target for sending transactions.
+    pub send: usize,
+
+    /// The number of leaders to target for establishing connections.
+    pub connect: usize,
+}
+
 /// Configuration for the [`ConnectionWorkersScheduler`].
 ///
 /// This struct holds the necessary settings to initialize and manage connection
@@ -66,10 +86,8 @@ pub struct ConnectionWorkersSchedulerConfig {
     /// connection failure.
     pub max_reconnect_attempts: usize,
 
-    /// The number of slots to look ahead during the leader estimation
-    /// procedure. Determines how far into the future leaders are estimated,
-    /// allowing connections to be established with those leaders in advance.
-    pub lookahead_slots: u64,
+    /// Configures the number of leaders to connect to and send transactions to.
+    pub leaders_fanout: Fanout,
 }
 
 impl ConnectionWorkersScheduler {
@@ -90,7 +108,7 @@ impl ConnectionWorkersScheduler {
             skip_check_transaction_age,
             worker_channel_size,
             max_reconnect_attempts,
-            lookahead_slots,
+            leaders_fanout,
         }: ConnectionWorkersSchedulerConfig,
         mut leader_updater: Box<dyn LeaderUpdater>,
         mut transaction_receiver: mpsc::Receiver<TransactionBatch>,
@@ -99,6 +117,7 @@ impl ConnectionWorkersScheduler {
         let endpoint = Self::setup_endpoint(bind, validator_identity)?;
         debug!("Client endpoint bind address: {:?}", endpoint.local_addr());
         let mut workers = WorkersCache::new(num_connections, cancel.clone());
+        let mut send_stats_per_addr = SendTransactionStatsPerAddr::new();
 
         loop {
             let transaction_batch = tokio::select! {
@@ -114,50 +133,49 @@ impl ConnectionWorkersScheduler {
                     break;
                 }
             };
-            let updated_leaders = leader_updater.next_leaders(lookahead_slots);
-            let new_leader = &updated_leaders[0];
-            let future_leaders = &updated_leaders[1..];
-            if !workers.contains(new_leader) {
-                debug!("No existing workers for {new_leader:?}, starting a new one.");
-                let worker = Self::spawn_worker(
-                    &endpoint,
-                    new_leader,
-                    worker_channel_size,
-                    skip_check_transaction_age,
-                    max_reconnect_attempts,
-                );
-                workers.push(*new_leader, worker).await;
-            }
 
-            tokio::select! {
-                send_res = workers.send_transactions_to_address(new_leader, transaction_batch) => match send_res {
-                    Ok(()) => (),
-                    Err(WorkersCacheError::ShutdownError) => {
-                        debug!("Connection to {new_leader} was closed, worker cache shutdown");
-                    }
-                    Err(err) => {
-                        warn!("Connection to {new_leader} was closed, worker error: {err}");
-                       // If we has failed to send batch, it will be dropped.
-                    }
-                },
-                () = cancel.cancelled() => {
-                    debug!("Cancelled: Shutting down");
-                    break;
-                }
-            };
+            let updated_leaders = leader_updater.next_leaders(leaders_fanout.connect);
 
-            // Regardless of who is leader, add future leaders to the cache to
-            // hide the latency of opening the connection.
-            for peer in future_leaders {
+            let (fanout_leaders, connect_leaders) =
+                split_leaders(&updated_leaders, &leaders_fanout);
+            // add future leaders to the cache to hide the latency of opening
+            // the connection.
+            for peer in connect_leaders {
                 if !workers.contains(peer) {
+                    let stats = send_stats_per_addr.entry(peer.ip()).or_default();
                     let worker = Self::spawn_worker(
                         &endpoint,
                         peer,
                         worker_channel_size,
                         skip_check_transaction_age,
                         max_reconnect_attempts,
+                        stats.clone(),
                     );
-                    workers.push(*peer, worker).await;
+                    maybe_shutdown_worker(workers.push(*peer, worker));
+                }
+            }
+
+            for new_leader in fanout_leaders {
+                if !workers.contains(new_leader) {
+                    warn!("No existing worker for {new_leader:?}, skip sending to this leader.");
+                    continue;
+                }
+
+                let send_res =
+                    workers.try_send_transactions_to_address(new_leader, transaction_batch.clone());
+                match send_res {
+                    Ok(()) => (),
+                    Err(WorkersCacheError::ShutdownError) => {
+                        debug!("Connection to {new_leader} was closed, worker cache shutdown");
+                    }
+                    Err(WorkersCacheError::ReceiverDropped) => {
+                        // Remove the worker from the cache, if the peer has disconnected.
+                        maybe_shutdown_worker(workers.pop(*new_leader));
+                    }
+                    Err(err) => {
+                        warn!("Connection to {new_leader} was closed, worker error: {err}");
+                        // If we has failed to send batch, it will be dropped.
+                    }
                 }
             }
         }
@@ -166,7 +184,7 @@ impl ConnectionWorkersScheduler {
 
         endpoint.close(0u32.into(), b"Closing connection");
         leader_updater.stop().await;
-        Ok(workers.transaction_stats().clone())
+        Ok(send_stats_per_addr)
     }
 
     /// Sets up the QUIC endpoint for the scheduler to handle connections.
@@ -191,6 +209,7 @@ impl ConnectionWorkersScheduler {
         worker_channel_size: usize,
         skip_check_transaction_age: bool,
         max_reconnect_attempts: usize,
+        stats: Arc<SendTransactionStats>,
     ) -> WorkerInfo {
         let (txs_sender, txs_receiver) = mpsc::channel(worker_channel_size);
         let endpoint = endpoint.clone();
@@ -202,12 +221,31 @@ impl ConnectionWorkersScheduler {
             txs_receiver,
             skip_check_transaction_age,
             max_reconnect_attempts,
+            stats,
         );
         let handle = tokio::spawn(async move {
             worker.run().await;
-            worker.transaction_stats().clone()
         });
 
         WorkerInfo::new(txs_sender, handle, cancel)
     }
 }
+
+/// Splits `leaders` into two slices based on the `fanout` configuration:
+/// * the first slice contains the leaders to which transactions will be sent,
+/// * the second vector contains the leaders, used to warm up connections. This
+///   slice includes the the first set.
+fn split_leaders<'leaders>(
+    leaders: &'leaders [SocketAddr],
+    fanout: &Fanout,
+) -> (&'leaders [SocketAddr], &'leaders [SocketAddr]) {
+    let Fanout { send, connect } = fanout;
+    assert!(send <= connect);
+    let send_count = (*send).min(leaders.len());
+    let connect_count = (*connect).min(leaders.len());
+
+    let send_slice = &leaders[..send_count];
+    let connect_slice = &leaders[..connect_count];
+
+    (send_slice, connect_slice)
+}

tpu-client-next/src/leader_updater.rs

@@ -13,6 +13,7 @@ use {
     log::*,
     solana_connection_cache::connection_cache::Protocol,
     solana_rpc_client::nonblocking::rpc_client::RpcClient,
+    solana_sdk::clock::NUM_CONSECUTIVE_LEADER_SLOTS,
     solana_tpu_client::nonblocking::tpu_client::LeaderTpuService,
     std::{
         fmt,
@@ -22,26 +23,30 @@ use {
             Arc,
         },
     },
+    thiserror::Error,
 };
 
 /// [`LeaderUpdater`] trait abstracts out functionality required for the
 /// [`ConnectionWorkersScheduler`](crate::ConnectionWorkersScheduler) to
 /// identify next leaders to send transactions to.
 #[async_trait]
 pub trait LeaderUpdater: Send {
-    /// Returns next unique leaders for the next `lookahead_slots` starting from
+    /// Returns next leaders for the next `lookahead_leaders` starting from
     /// current estimated slot.
     ///
+    /// Leaders are returned per [`NUM_CONSECUTIVE_LEADER_SLOTS`] to avoid unnecessary repetition.
+    ///
     /// If the current leader estimation is incorrect and transactions are sent to
     /// only one estimated leader, there is a risk of losing all the transactions,
     /// depending on the forwarding policy.
-    fn next_leaders(&self, lookahead_slots: u64) -> Vec<SocketAddr>;
+    fn next_leaders(&mut self, lookahead_leaders: usize) -> Vec<SocketAddr>;
 
     /// Stop [`LeaderUpdater`] and releases all associated resources.
     async fn stop(&mut self);
 }
 
 /// Error type for [`LeaderUpdater`].
+#[derive(Error, PartialEq)]
 pub struct LeaderUpdaterError;
 
 impl fmt::Display for LeaderUpdaterError {
@@ -98,7 +103,9 @@ struct LeaderUpdaterService {
 
 #[async_trait]
 impl LeaderUpdater for LeaderUpdaterService {
-    fn next_leaders(&self, lookahead_slots: u64) -> Vec<SocketAddr> {
+    fn next_leaders(&mut self, lookahead_leaders: usize) -> Vec<SocketAddr> {
+        let lookahead_slots =
+            (lookahead_leaders as u64).saturating_mul(NUM_CONSECUTIVE_LEADER_SLOTS);
         self.leader_tpu_service.leader_tpu_sockets(lookahead_slots)
     }
 
@@ -116,7 +123,7 @@ struct PinnedLeaderUpdater {
 
 #[async_trait]
 impl LeaderUpdater for PinnedLeaderUpdater {
-    fn next_leaders(&self, _lookahead_slots: u64) -> Vec<SocketAddr> {
+    fn next_leaders(&mut self, _lookahead_leaders: usize) -> Vec<SocketAddr> {
         self.address.clone()
     }