feat: implement performance-based peer selection for snap sync (#9722)

- Add peer performance metrics (latency, throughput) to EthPeer and EthPeerImmutableAttributes
- Capture latency and throughput in AbstractPeerRequestTask
- Add performance-based comparators (BY_LOW_LATENCY, BY_TRANSFER_SPEED) to EthPeers
- Update AbstractRetryingSwitchingPeerTask to support custom comparators
- Integrate performance-based selection into Snap Sync tasks and RequestDataStep
- Add comprehensive unit tests for peer selection and metrics capturing

Signed-off-by: Bruno Coste <bcoste@gmail.com>

Author: bcoste

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/manager/EthPeer.java

@@ -94,6 +94,9 @@ protected boolean removeEldestEntry(final Map.Entry<Hash, Boolean> eldest) {
   private final AtomicInteger lastProtocolVersion = new AtomicInteger(0);
 
   private volatile long lastRequestTimestamp = 0;
+  private static final double ALPHA = 0.1;
+  private volatile double averageLatencyMs = -1.0;
+  private volatile double averageThroughputBytesPerSecond = -1.0;
 
   private final Map<String, Map<Integer, RequestManager>> requestManagers;
 
@@ -224,6 +227,33 @@ public void recordUsefulResponse() {
     reputation.recordUsefulResponse();
   }
 
+  public void recordLatency(final double latencyMs) {
+    if (averageLatencyMs < 0) {
+      averageLatencyMs = latencyMs;
+    } else {
+      averageLatencyMs = (ALPHA * latencyMs) + ((1.0 - ALPHA) * averageLatencyMs);
+    }
+  }
+
+  public void recordThroughput(final long bytes, final double durationMs) {
+    if (durationMs <= 0) return;
+    double throughput = (bytes * 1000.0) / durationMs;
+    if (averageThroughputBytesPerSecond < 0) {
+      averageThroughputBytesPerSecond = throughput;
+    } else {
+      averageThroughputBytesPerSecond =
+          (ALPHA * throughput) + ((1.0 - ALPHA) * averageThroughputBytesPerSecond);
+    }
+  }
+
+  public double getAverageLatencyMs() {
+    return averageLatencyMs;
+  }
+
+  public double getAverageThroughputBytesPerSecond() {
+    return averageThroughputBytesPerSecond;
+  }
+
   public void disconnect(final DisconnectReason reason) {
     connection.disconnect(reason);
   }

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/manager/EthPeerImmutableAttributes.java

@@ -28,6 +28,8 @@ public record EthPeerImmutableAttributes(
     boolean isServingSnap,
     boolean hasAvailableRequestCapacity,
     boolean isInboundInitiated,
+    double averageLatencyMs,
+    double averageThroughputBytesPerSecond,
     EthPeer ethPeer) {
 
   public static EthPeerImmutableAttributes from(final EthPeer peer) {
@@ -43,6 +45,8 @@ public static EthPeerImmutableAttributes from(final EthPeer peer) {
         peer.isServingSnap(),
         peer.hasAvailableRequestCapacity(),
         peer.getConnection().inboundInitiated(),
+        peer.getAverageLatencyMs(),
+        peer.getAverageThroughputBytesPerSecond(),
         peer);
   }
 }

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/manager/EthPeers.java

@@ -85,6 +85,16 @@ public class EthPeers implements PeerSelector {
   public static final Comparator<EthPeerImmutableAttributes> LEAST_TO_MOST_BUSY =
       Comparator.comparing(EthPeerImmutableAttributes::outstandingRequests)
           .thenComparing(EthPeerImmutableAttributes::lastRequestTimestamp);
+
+  public static final Comparator<EthPeerImmutableAttributes> BY_LOW_LATENCY =
+      Comparator.comparing(
+              (final EthPeerImmutableAttributes p) ->
+                  p.averageLatencyMs() < 0 ? Double.MAX_VALUE : p.averageLatencyMs())
+          .reversed();
+
+  public static final Comparator<EthPeerImmutableAttributes> BY_HIGH_THROUGHPUT =
+      Comparator.comparing(EthPeerImmutableAttributes::averageThroughputBytesPerSecond);
+
   public static final int NODE_ID_LENGTH = 64;
   public static final int USEFULL_PEER_SCORE_THRESHOLD = 102;
 
@@ -373,9 +383,14 @@ public Stream<EthPeerImmutableAttributes> streamAvailablePeers() {
   }
 
   public Stream<EthPeerImmutableAttributes> streamBestPeers() {
+    return streamBestPeers(getBestPeerComparator());
+  }
+
+  public Stream<EthPeerImmutableAttributes> streamBestPeers(
+      final Comparator<EthPeerImmutableAttributes> comparator) {
     return streamAvailablePeers()
         .filter(EthPeerImmutableAttributes::isFullyValidated)
-        .sorted(getBestPeerComparator().reversed());
+        .sorted(comparator.reversed());
   }
 
   public Optional<EthPeer> bestPeer() {

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/manager/task/AbstractPeerRequestTask.java

@@ -42,6 +42,7 @@ public abstract class AbstractPeerRequestTask<R> extends AbstractPeerTask<R> {
   private final String protocolName;
   private final int requestCode;
   private volatile PendingPeerRequest responseStream;
+  private long startTimeNanos;
 
   protected AbstractPeerRequestTask(
       final EthContext ethContext,
@@ -64,6 +65,7 @@ protected final void executeTask() {
     responseStream = sendRequest();
     responseStream.then(
         stream -> {
+          startTimeNanos = System.nanoTime();
           // Start the timeout now that the request has actually been sent
           ethContext.getScheduler().failAfterTimeout(promise, timeout);
 
@@ -108,6 +110,9 @@ private void handleMessage(
       final Optional<R> result = processResponse(streamClosed, message, peer);
       result.ifPresent(
           r -> {
+            final double durationMs = (System.nanoTime() - startTimeNanos) / 1_000_000.0;
+            peer.recordLatency(durationMs);
+            peer.recordThroughput(message.getSize(), durationMs);
             promise.complete(r);
             peer.recordUsefulResponse();
           });

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/manager/task/AbstractRetryingSwitchingPeerTask.java

@@ -39,6 +39,7 @@ public abstract class AbstractRetryingSwitchingPeerTask<T> extends AbstractRetry
 
   private final Set<EthPeer> triedPeers = new HashSet<>();
   private final Set<EthPeer> failedPeers = new HashSet<>();
+  private Optional<Comparator<EthPeerImmutableAttributes>> peerComparator = Optional.empty();
 
   protected AbstractRetryingSwitchingPeerTask(
       final EthContext ethContext,
@@ -100,6 +101,10 @@ protected CompletableFuture<T> executePeerTask(final Optional<EthPeer> assignedP
             });
   }
 
+  public void setPeerComparator(final Comparator<EthPeerImmutableAttributes> peerComparator) {
+    this.peerComparator = Optional.of(peerComparator);
+  }
+
   @Override
   protected void handleTaskError(final Throwable error) {
     if (isPeerFailure(error)) {
@@ -129,7 +134,8 @@ private Optional<EthPeer> selectNextPeer() {
   protected Optional<EthPeer> nextPeerToTry() {
     return getEthContext()
         .getEthPeers()
-        .streamBestPeers()
+        .streamBestPeers(
+            peerComparator.orElse(getEthContext().getEthPeers().getBestPeerComparator()))
         .filter((peer) -> isSuitablePeer(peer) && !triedPeers.contains(peer.ethPeer()))
         .map(EthPeerImmutableAttributes::ethPeer)
         .findFirst();

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/sync/snapsync/RequestDataStep.java

@@ -17,6 +17,7 @@
 import org.hyperledger.besu.datatypes.Hash;
 import org.hyperledger.besu.ethereum.core.BlockHeader;
 import org.hyperledger.besu.ethereum.eth.manager.EthContext;
+import org.hyperledger.besu.ethereum.eth.manager.EthPeers;
 import org.hyperledger.besu.ethereum.eth.manager.snap.RetryingGetAccountRangeFromPeerTask;
 import org.hyperledger.besu.ethereum.eth.manager.snap.RetryingGetBytecodeFromPeerTask;
 import org.hyperledger.besu.ethereum.eth.manager.snap.RetryingGetStorageRangeFromPeerTask;
@@ -92,9 +93,11 @@ public CompletableFuture<Task<SnapDataRequest>> requestAccount(
             ethContext,
             accountDataRequest.getStartKeyHash(),
             accountDataRequest.getEndKeyHash(),
-            blockHeader,
+             blockHeader,
             metricsSystem);
+    ((RetryingGetAccountRangeFromPeerTask) getAccountTask).setPeerComparator(EthPeers.BY_HIGH_THROUGHPUT);
     downloadState.addOutstandingTask(getAccountTask);
+
     return getAccountTask
         .run()
         .orTimeout(10, TimeUnit.SECONDS)
@@ -142,6 +145,8 @@ public CompletableFuture<List<Task<SnapDataRequest>>> requestStorage(
     final EthTask<StorageRangeMessage.SlotRangeData> getStorageRangeTask =
         RetryingGetStorageRangeFromPeerTask.forStorageRange(
             ethContext, accountHashesAsBytes32, minRange, maxRange, blockHeader, metricsSystem);
+    ((RetryingGetStorageRangeFromPeerTask) getStorageRangeTask)
+        .setPeerComparator(EthPeers.BY_HIGH_THROUGHPUT);
     downloadState.addOutstandingTask(getStorageRangeTask);
     return getStorageRangeTask
         .run()
@@ -203,6 +208,7 @@ public CompletableFuture<List<Task<SnapDataRequest>>> requestCode(
     final EthTask<Map<Bytes32, Bytes>> getByteCodeTask =
         RetryingGetBytecodeFromPeerTask.forByteCode(
             ethContext, codeHashes, blockHeader, metricsSystem);
+    ((RetryingGetBytecodeFromPeerTask) getByteCodeTask).setPeerComparator(EthPeers.BY_LOW_LATENCY);
     downloadState.addOutstandingTask(getByteCodeTask);
     return getByteCodeTask
         .run()
@@ -249,6 +255,8 @@ public CompletableFuture<List<Task<SnapDataRequest>>> requestTrieNodeByPath(
     final EthTask<Map<Bytes, Bytes>> getTrieNodeFromPeerTask =
         RetryingGetTrieNodeFromPeerTask.forTrieNodes(
             ethContext, message, blockHeader, metricsSystem);
+    ((RetryingGetTrieNodeFromPeerTask) getTrieNodeFromPeerTask)
+        .setPeerComparator(EthPeers.BY_LOW_LATENCY);
     downloadState.addOutstandingTask(getTrieNodeFromPeerTask);
     return getTrieNodeFromPeerTask
         .run()

ethereum/eth/src/test/java/org/hyperledger/besu/ethereum/eth/manager/EthPeerTest.java

@@ -392,6 +392,39 @@ public void recordUsefulResponse() {
     assertThat(peer.getReputation().compareTo(peer2.getReputation())).isGreaterThan(0);
   }
 
+  @Test
+  public void shouldRecordLatencyAndThroughput() {
+    final EthPeer peer = createPeer();
+    assertThat(peer.getAverageLatencyMs()).isEqualTo(-1.0);
+    assertThat(peer.getAverageThroughputBytesPerSecond()).isEqualTo(-1.0);
+
+    // First record sets the value
+    peer.recordLatency(100.0);
+    assertThat(peer.getAverageLatencyMs()).isEqualTo(100.0);
+
+    // Second record updates EMA: 0.1 * 200 + 0.9 * 100 = 110
+    peer.recordLatency(200.0);
+    assertThat(peer.getAverageLatencyMs()).isEqualTo(110.0);
+
+    // First record sets throughput
+    // 1000 bytes in 100ms = 10,000 bytes/s
+    peer.recordThroughput(1000, 100.0);
+    assertThat(peer.getAverageThroughputBytesPerSecond()).isEqualTo(10000.0);
+
+    // Second record updates EMA
+    // 2000 bytes in 100ms = 20,000 bytes/s
+    // EMA: 0.1 * 20000 + 0.9 * 10000 = 11000
+    peer.recordThroughput(2000, 100.0);
+    assertThat(peer.getAverageThroughputBytesPerSecond()).isEqualTo(11000.0);
+  }
+
+  @Test
+  public void shouldHandleZeroDurationInThroughput() {
+    final EthPeer peer = createPeer();
+    peer.recordThroughput(1000, 0.0);
+    assertThat(peer.getAverageThroughputBytesPerSecond()).isEqualTo(-1.0);
+  }
+
   private void messageStream(
       final ResponseStreamSupplier getStream,
       final MessageData targetMessage,

ethereum/eth/src/test/java/org/hyperledger/besu/ethereum/eth/manager/EthPeersTest.java

@@ -125,6 +125,63 @@ public void comparesPeersWithTdAndNoHeight() {
         .isEmpty();
   }
 
+  @Test
+  public void comparesPeersByLatency() {
+    final EthPeer peerA =
+        EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1000).getEthPeer();
+    final EthPeer peerB =
+        EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1000).getEthPeer();
+
+    peerA.recordLatency(100.0);
+    peerB.recordLatency(200.0);
+
+    final EthPeerImmutableAttributes attrA = EthPeerImmutableAttributes.from(peerA);
+    final EthPeerImmutableAttributes attrB = EthPeerImmutableAttributes.from(peerB);
+
+    // Smaller latency is better, so attrA > attrB in LOW_LATENCY comparator
+    assertThat(EthPeers.BY_LOW_LATENCY.compare(attrA, attrB)).isGreaterThan(0);
+    assertThat(EthPeers.BY_LOW_LATENCY.compare(attrB, attrA)).isLessThan(0);
+
+    // Peer with unknown latency should be worse than any known latency
+    final EthPeer peerC =
+        EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1000).getEthPeer();
+    final EthPeerImmutableAttributes attrC = EthPeerImmutableAttributes.from(peerC);
+    assertThat(EthPeers.BY_LOW_LATENCY.compare(attrA, attrC)).isGreaterThan(0);
+  }
+
+  @Test
+  public void comparesPeersByThroughput() {
+    final EthPeer peerA =
+        EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1000).getEthPeer();
+    final EthPeer peerB =
+        EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1000).getEthPeer();
+
+    peerA.recordThroughput(2000, 1000.0); // 2000 bytes/s
+    peerB.recordThroughput(1000, 1000.0); // 1000 bytes/s
+
+    final EthPeerImmutableAttributes attrA = EthPeerImmutableAttributes.from(peerA);
+    final EthPeerImmutableAttributes attrB = EthPeerImmutableAttributes.from(peerB);
+
+    // Larger throughput is better
+    assertThat(EthPeers.BY_HIGH_THROUGHPUT.compare(attrA, attrB)).isGreaterThan(0);
+    assertThat(EthPeers.BY_HIGH_THROUGHPUT.compare(attrB, attrA)).isLessThan(0);
+  }
+
+  @Test
+  public void shouldStreamBestPeersWithCustomComparator() {
+    final EthPeer peerA =
+        EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1000).getEthPeer();
+    final EthPeer peerB =
+        EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1000).getEthPeer();
+
+    peerA.recordLatency(200.0);
+    peerB.recordLatency(100.0);
+
+    // BY_LOW_LATENCY reversed should put peerB first
+    assertThat(ethPeers.streamBestPeers(EthPeers.BY_LOW_LATENCY).findFirst())
+        .contains(EthPeerImmutableAttributes.from(peerB));
+  }
+
   @Test
   public void shouldExecutePeerRequestImmediatelyWhenPeerIsAvailable() throws Exception {
     final RespondingEthPeer peer = EthProtocolManagerTestUtil.createPeer(ethProtocolManager, 1000);