Networking improvements: cached known peers, fewer DB accesses, EPC spawn-failure hook

src/main/java/org/qortal/api/ApiError.java

@@ -15,6 +15,7 @@ public enum ApiError {
 	REPOSITORY_ISSUE(5, 500),
 	NON_PRODUCTION(6, 403),
 	BLOCKCHAIN_NEEDS_SYNC(7, 503),
+	NO_TIME_SYNC(8, 503),
 
 	// VALIDATION
 	INVALID_SIGNATURE(101, 400),

src/main/java/org/qortal/api/resource/PeersResource.java

@@ -8,6 +8,7 @@ import io.swagger.v3.oas.annotations.parameters.RequestBody;
 import io.swagger.v3.oas.annotations.responses.ApiResponse;
 import io.swagger.v3.oas.annotations.tags.Tag;
 
+import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Collectors;
 
@@ -29,9 +30,8 @@ import org.qortal.data.network.PeerData;
 import org.qortal.network.Network;
 import org.qortal.network.PeerAddress;
 import org.qortal.repository.DataException;
-import org.qortal.repository.Repository;
-import org.qortal.repository.RepositoryManager;
 import org.qortal.utils.ExecuteProduceConsume;
+import org.qortal.utils.NTP;
 
 @Path("/peers")
 @Tag(name = "Peers")
@@ -81,11 +81,7 @@ public class PeersResource {
 		ApiError.REPOSITORY_ISSUE
 	})
 	public List<PeerData> getKnownPeers() {
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			return repository.getNetworkRepository().getAllPeers();
-		} catch (DataException e) {
-			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
-		}
+		return Network.getInstance().getAllKnownPeers();
 	}
 
 	@GET
@@ -166,12 +162,14 @@ public class PeersResource {
 	public String addPeer(String address) {
 		Security.checkApiCallAllowed(request);
 
-		try (final Repository repository = RepositoryManager.getRepository()) {
+		final Long addedWhen = NTP.getTime();
+		if (addedWhen == null)
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.NO_TIME_SYNC);
+
+		try {
 			PeerAddress peerAddress = PeerAddress.fromString(address);
 
-			PeerData peerData = new PeerData(peerAddress, System.currentTimeMillis(), "API");
-			repository.getNetworkRepository().save(peerData);
-			repository.saveChanges();
+			Network.getInstance().mergePeers("API", addedWhen, Arrays.asList(peerAddress));
 
 			return "true";
 		} catch (IllegalArgumentException e) {

src/main/java/org/qortal/controller/Controller.java

@@ -336,7 +336,7 @@ public class Controller extends Thread {
 		try {
 			Network network = Network.getInstance();
 			network.start();
-		} catch (IOException e) {
+		} catch (IOException | DataException e) {
 			LOGGER.error("Unable to start networking", e);
 			Controller.getInstance().shutdown();
 			Gui.getInstance().fatalError("Networking failure", e);
@@ -549,17 +549,7 @@ public class Controller extends Thread {
 					LOGGER.info(String.format("Failed to synchronize with peer %s (%s) - cooling off", peer, syncResult.name()));
 
 					// Don't use this peer again for a while
-					PeerData peerData = peer.getPeerData();
-					peerData.setLastMisbehaved(NTP.getTime());
-
-					// Only save to repository if outbound peer
-					if (peer.isOutbound())
-						try (final Repository repository = RepositoryManager.getRepository()) {
-							repository.getNetworkRepository().save(peerData);
-							repository.saveChanges();
-						} catch (DataException e) {
-							LOGGER.warn("Repository issue while updating peer synchronization info", e);
-						}
+					Network.getInstance().peerMisbehaved(peer);
 					break;
 				}
 

src/main/java/org/qortal/network/Network.java

@@ -7,7 +7,6 @@ import java.net.InetSocketAddress;
 import java.net.StandardSocketOptions;
 import java.net.UnknownHostException;
 import java.nio.channels.CancelledKeyException;
-import java.nio.channels.ClosedChannelException;
 import java.nio.channels.SelectionKey;
 import java.nio.channels.Selector;
 import java.nio.channels.ServerSocketChannel;
@@ -56,6 +55,7 @@ import org.qortal.repository.Repository;
 import org.qortal.repository.RepositoryManager;
 import org.qortal.settings.Settings;
 import org.qortal.utils.ExecuteProduceConsume;
+import org.qortal.utils.ExecutorDumper;
 import org.qortal.utils.ExecuteProduceConsume.StatsSnapshot;
 import org.qortal.utils.NTP;
 
@@ -104,6 +104,8 @@ public class Network {
 
 	private final byte[] ourPeerId;
 	private final int maxMessageSize;
+
+	private List<PeerData> allKnownPeers;
 	private List<Peer> connectedPeers;
 	private List<PeerAddress> selfPeers;
 
@@ -152,7 +154,7 @@ public class Network {
 		networkEPC = new NetworkProcessor(networkExecutor);
 	}
 
-	public void start() throws IOException {
+	public void start() throws IOException, DataException {
 		// Grab P2P port from settings
 		int listenPort = Settings.getInstance().getListenPort();
 
@@ -177,6 +179,11 @@ public class Network {
 			throw new IOException("Can't create listen socket", e);
 		}
 
+		// Load all known peers from repository
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			allKnownPeers = repository.getNetworkRepository().getAllPeers();
+		}
+
 		// Start up first networking thread
 		networkEPC.start();
 	}
@@ -209,6 +216,12 @@ public class Network {
 
 	// Peer lists
 
+	public List<PeerData> getAllKnownPeers() {
+		synchronized (this.allKnownPeers) {
+			return new ArrayList<>(this.allKnownPeers);
+		}
+	}
+
 	public List<Peer> getConnectedPeers() {
 		synchronized (this.connectedPeers) {
 			return new ArrayList<>(this.connectedPeers);
@@ -223,24 +236,16 @@ public class Network {
 
 	/** Returns list of connected peers that have completed handshaking. */
 	public List<Peer> getHandshakedPeers() {
-		List<Peer> peers = new ArrayList<>();
-
 		synchronized (this.connectedPeers) {
-			peers = this.connectedPeers.stream().filter(peer -> peer.getHandshakeStatus() == Handshake.COMPLETED).collect(Collectors.toList());
+			return this.connectedPeers.stream().filter(peer -> peer.getHandshakeStatus() == Handshake.COMPLETED).collect(Collectors.toList());
 		}
-
-		return peers;
 	}
 
 	/** Returns list of connected peers that have completed handshaking, with inbound duplicates removed. */
 	public List<Peer> getUniqueHandshakedPeers() {
-		final List<Peer> peers;
+		List<Peer> peers = getHandshakedPeers();
 
-		synchronized (this.connectedPeers) {
-			peers = this.connectedPeers.stream().filter(peer -> peer.getHandshakeStatus() == Handshake.COMPLETED).collect(Collectors.toList());
-		}
-
-		// Returns true if this [inbound] peer has corresponding outbound peer with same ID
+		// Returns true if this peer is inbound and has corresponding outbound peer with same ID
 		Predicate<Peer> hasOutboundWithSameId = peer -> {
 			// Peer is outbound so return fast
 			if (peer.isOutbound())
@@ -249,7 +254,7 @@ public class Network {
 			return peers.stream().anyMatch(otherPeer -> otherPeer.isOutbound() && Arrays.equals(otherPeer.getPeerId(), peer.getPeerId()));
 		};
 
-		// Filter out [inbound] peers that have corresponding outbound peer with the same ID
+		// Filter out inbound peers that have corresponding outbound peer with the same ID
 		peers.removeIf(hasOutboundWithSameId);
 
 		return peers;
@@ -276,6 +281,32 @@ public class Network {
 		}
 	}
 
+
+	// Peer list filters
+
+	/** Must be inside <tt>synchronized (this.selfPeers) {...}</tt> */
+	private final Predicate<PeerData> isSelfPeer = peerData -> {
+		PeerAddress peerAddress = peerData.getAddress();
+		return this.selfPeers.stream().anyMatch(selfPeer -> selfPeer.equals(peerAddress));
+	};
+
+	/** Must be inside <tt>synchronized (this.connectedPeers) {...}</tt> */
+	private final Predicate<PeerData> isConnectedPeer = peerData -> {
+		PeerAddress peerAddress = peerData.getAddress();
+		return this.connectedPeers.stream().anyMatch(peer -> peer.getPeerData().getAddress().equals(peerAddress));
+	};
+
+	/** Must be inside <tt>synchronized (this.connectedPeers) {...}</tt> */
+	private final Predicate<PeerData> isResolvedAsConnectedPeer = peerData -> {
+		try {
+			InetSocketAddress resolvedSocketAddress = peerData.getAddress().toSocketAddress();
+			return this.connectedPeers.stream().anyMatch(peer -> peer.getResolvedAddress().equals(resolvedSocketAddress));
+		} catch (UnknownHostException e) {
+			// Can't resolve - no point even trying to connect
+			return true;
+		}
+	};
+
 	// Initial setup
 
 	public static void installInitialPeers(Repository repository) throws DataException {
@@ -297,6 +328,12 @@ public class Network {
 			super(executor);
 		}
 
+		@Override
+		protected void onSpawnFailure() {
+			// For debugging:
+			// ExecutorDumper.dump(this.executor, 3, ExecuteProduceConsume.class);
+		}
+
 		@Override
 		protected Task produceTask(boolean canBlock) throws InterruptedException {
 			Task task;
@@ -504,7 +541,7 @@ public class Network {
 
 				LOGGER.debug(() -> String.format("Connection accepted from peer %s", PeerAddress.fromSocket(socketChannel.socket())));
 
-				newPeer = new Peer(socketChannel);
+				newPeer = new Peer(socketChannel, channelSelector);
 				this.connectedPeers.add(newPeer);
 			}
 		} catch (IOException e) {
@@ -512,105 +549,15 @@ public class Network {
 				try {
 					socketChannel.close();
 				} catch (IOException ce) {
+					// Couldn't close?
 				}
 
 			return;
 		}
 
-		try {
-			socketChannel.setOption(StandardSocketOptions.TCP_NODELAY, true);
-			socketChannel.configureBlocking(false);
-			socketChannel.register(channelSelector, SelectionKey.OP_READ);
-		} catch (IOException e) {
-			// Remove from connected peers
-			synchronized (this.connectedPeers) {
-				this.connectedPeers.remove(newPeer);
-			}
-
-			return;
-		}
-
 		this.onPeerReady(newPeer);
 	}
 
-	public void prunePeers() throws InterruptedException, DataException {
-		final Long now = NTP.getTime();
-		if (now == null)
-			return;
-
-		// Disconnect peers that are stuck during handshake
-		List<Peer> handshakePeers = this.getConnectedPeers();
-
-		// Disregard peers that have completed handshake or only connected recently
-		handshakePeers.removeIf(peer -> peer.getHandshakeStatus() == Handshake.COMPLETED || peer.getConnectionTimestamp() == null || peer.getConnectionTimestamp() > now - HANDSHAKE_TIMEOUT);
-
-		for (Peer peer : handshakePeers)
-			peer.disconnect(String.format("handshake timeout at %s", peer.getHandshakeStatus().name()));
-
-		// Prune 'old' peers from repository...
-		// Pruning peers isn't critical so no need to block for a repository instance.
-		try (final Repository repository = RepositoryManager.tryRepository()) {
-			if (repository == null)
-				return;
-
-			// Fetch all known peers
-			List<PeerData> peers = repository.getNetworkRepository().getAllPeers();
-
-			// 'Old' peers:
-			// we have attempted to connect within the last day
-			// we last managed to connect over a week ago
-			Predicate<PeerData> isNotOldPeer = peerData -> {
-				if (peerData.getLastAttempted() == null || peerData.getLastAttempted() < now - OLD_PEER_ATTEMPTED_PERIOD)
-					return true;
-
-				if (peerData.getLastConnected() == null || peerData.getLastConnected() > now - OLD_PEER_CONNECTION_PERIOD)
-					return true;
-
-				return false;
-			};
-
-			// Disregard peers that are NOT 'old'
-			peers.removeIf(isNotOldPeer);
-
-			// Don't consider already connected peers (simple address match)
-			Predicate<PeerData> isConnectedPeer = peerData -> {
-				PeerAddress peerAddress = peerData.getAddress();
-				return this.connectedPeers.stream().anyMatch(peer -> peer.getPeerData().getAddress().equals(peerAddress));
-			};
-
-			synchronized (this.connectedPeers) {
-				peers.removeIf(isConnectedPeer);
-			}
-
-			for (PeerData peerData : peers) {
-				LOGGER.debug(String.format("Deleting old peer %s from repository", peerData.getAddress().toString()));
-				repository.getNetworkRepository().delete(peerData.getAddress());
-			}
-
-			repository.saveChanges();
-		}
-	}
-
-	private final Predicate<PeerData> isSelfPeer = peerData -> {
-		PeerAddress peerAddress = peerData.getAddress();
-		return this.selfPeers.stream().anyMatch(selfPeer -> selfPeer.equals(peerAddress));
-	};
-
-	private final Predicate<PeerData> isConnectedPeer = peerData -> {
-		PeerAddress peerAddress = peerData.getAddress();
-		return this.connectedPeers.stream().anyMatch(peer -> peer.getPeerData().getAddress().equals(peerAddress));
-	};
-
-	private final Predicate<PeerData> isResolvedAsConnectedPeer = peerData -> {
-		try {
-			InetSocketAddress resolvedSocketAddress = peerData.getAddress().toSocketAddress();
-			return this.connectedPeers.stream().anyMatch(peer -> peer.getResolvedAddress().equals(resolvedSocketAddress));
-		} catch (UnknownHostException e) {
-			// Can't resolve - no point even trying to connect
-			return true;
-		}
-	};
-
 	private Peer getConnectablePeer(final Long now) throws InterruptedException {
 		// We can't block here so use tryRepository(). We don't NEED to connect a new peer.
 		try (final Repository repository = RepositoryManager.tryRepository()) {
@@ -618,7 +565,7 @@ public class Network {
 				return null;
 
 			// Find an address to connect to
-			List<PeerData> peers = repository.getNetworkRepository().getAllPeers();
+			List<PeerData> peers = this.getAllKnownPeers();
 
 			// Don't consider peers with recent connection failures
 			final long lastAttemptedThreshold = now - CONNECT_FAILURE_BACKOFF;
@@ -631,14 +578,12 @@ public class Network {
 				peers.removeIf(isSelfPeer);
 			}
 
-			// Don't consider already connected peers (simple address match)
 			synchronized (this.connectedPeers) {
+				// Don't consider already connected peers (simple address match)
 				peers.removeIf(isConnectedPeer);
-			}
 
-			// Don't consider already connected peers (resolved address match)
-			// XXX This might be too slow if we end up waiting a long time for hostnames to resolve via DNS
-			synchronized (this.connectedPeers) {
+				// Don't consider already connected peers (resolved address match)
+				// XXX This might be too slow if we end up waiting a long time for hostnames to resolve via DNS
 				peers.removeIf(isResolvedAsConnectedPeer);
 			}
 
@@ -647,17 +592,18 @@ public class Network {
 				return null;
 
 			// Pick random peer
-			int peerIndex = new SecureRandom().nextInt(peers.size());
+			int peerIndex = new Random().nextInt(peers.size());
 
 			// Pick candidate
 			PeerData peerData = peers.get(peerIndex);
 			Peer newPeer = new Peer(peerData);
 
 			// Update connection attempt info
-			repository.discardChanges();
 			peerData.setLastAttempted(now);
-			repository.getNetworkRepository().save(peerData);
-			repository.saveChanges();
+			synchronized (this.allKnownPeers) {
+				repository.getNetworkRepository().save(peerData);
+				repository.saveChanges();
+			}
 
 			return newPeer;
 		} catch (DataException e) {
@@ -667,7 +613,7 @@ public class Network {
 	}
 
 	private void connectPeer(Peer newPeer) throws InterruptedException {
-		SocketChannel socketChannel = newPeer.connect();
+		SocketChannel socketChannel = newPeer.connect(this.channelSelector);
 		if (socketChannel == null)
 			return;
 
@@ -678,15 +624,6 @@ public class Network {
 			this.connectedPeers.add(newPeer);
 		}
 
-		try {
-			socketChannel.register(channelSelector, SelectionKey.OP_READ);
-		} catch (ClosedChannelException e) {
-			// If channel has somehow already closed then remove from connectedPeers
-			synchronized (this.connectedPeers) {
-				this.connectedPeers.remove(newPeer);
-			}
-		}
-
 		this.onPeerReady(newPeer);
 	}
 
@@ -718,15 +655,21 @@ public class Network {
 		synchronized (this.connectedPeers) {
 			this.connectedPeers.remove(peer);
 		}
+	}
 
-		// If this is an inbound peer then remove from known peers list
-		// as remote port is not likely to be remote peer's listen port
-		if (!peer.isOutbound())
+	public void peerMisbehaved(Peer peer) {
+		PeerData peerData = peer.getPeerData();
+		peerData.setLastMisbehaved(NTP.getTime());
+
+		// Only update repository if outbound peer
+		if (peer.isOutbound())
 			try (final Repository repository = RepositoryManager.getRepository()) {
-				repository.getNetworkRepository().delete(peer.getPeerData().getAddress());
-				repository.saveChanges();
+				synchronized (this.allKnownPeers) {
+					repository.getNetworkRepository().save(peerData);
+					repository.saveChanges();
+				}
 			} catch (DataException e) {
-				LOGGER.error(String.format("Repository issue while trying to delete inbound peer %s", peer), e);
+				LOGGER.warn("Repository issue while updating peer synchronization info", e);
 			}
 	}
 
@@ -828,7 +771,7 @@ public class Network {
 
 	private void onGetPeersMessage(Peer peer, Message message) {
 		// Send our known peers
-		if (!peer.sendMessage(buildPeersMessage(peer)))
+		if (!peer.sendMessage(this.buildPeersMessage(peer)))
 			peer.disconnect("failed to send peers list");
 	}
 
@@ -845,7 +788,7 @@ public class Network {
 		// Also add peer's details
 		peerAddresses.add(PeerAddress.fromString(peer.getPeerData().getAddress().getHost()));
 
-		mergePeers(peer.toString(), peerAddresses);
+		opportunisticMergePeers(peer.toString(), peerAddresses);
 	}
 
 	private void onPingMessage(Peer peer, Message message) {
@@ -875,7 +818,7 @@ public class Network {
 			peerV2Addresses.add(0, sendingPeerAddress);
 		}
 
-		mergePeers(peer.toString(), peerV2Addresses);
+		opportunisticMergePeers(peer.toString(), peerV2Addresses);
 	}
 
 	private void onPeerVerifyMessage(Peer peer, Message message) {
@@ -925,8 +868,10 @@ public class Network {
 		// Update connection info for outbound peers only
 		if (peer.isOutbound())
 			try (final Repository repository = RepositoryManager.getRepository()) {
-				repository.getNetworkRepository().save(peer.getPeerData());
-				repository.saveChanges();
+				synchronized (this.allKnownPeers) {
+					repository.getNetworkRepository().save(peer.getPeerData());
+					repository.saveChanges();
+				}
 			} catch (DataException e) {
 				LOGGER.error(String.format("Repository issue while trying to update outbound peer %s", peer), e);
 			}
@@ -964,77 +909,72 @@ public class Network {
 
 	/** Returns PEERS message made from peers we've connected to recently, and this node's details */
 	public Message buildPeersMessage(Peer peer) {
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			List<PeerData> knownPeers = repository.getNetworkRepository().getAllPeers();
+		List<PeerData> knownPeers = this.getAllKnownPeers();
 
-			// Filter out peers that we've not connected to ever or within X milliseconds
-			final long connectionThreshold = NTP.getTime() - RECENT_CONNECTION_THRESHOLD;
-			Predicate<PeerData> notRecentlyConnected = peerData -> {
-				final Long lastAttempted = peerData.getLastAttempted();
-				final Long lastConnected = peerData.getLastConnected();
+		// Filter out peers that we've not connected to ever or within X milliseconds
+		final long connectionThreshold = NTP.getTime() - RECENT_CONNECTION_THRESHOLD;
+		Predicate<PeerData> notRecentlyConnected = peerData -> {
+			final Long lastAttempted = peerData.getLastAttempted();
+			final Long lastConnected = peerData.getLastConnected();
 
-				if (lastAttempted == null || lastConnected == null)
-					return true;
+			if (lastAttempted == null || lastConnected == null)
+				return true;
 
-				if (lastConnected < lastAttempted)
-					return true;
+			if (lastConnected < lastAttempted)
+				return true;
 
-				if (lastConnected < connectionThreshold)
-					return true;
+			if (lastConnected < connectionThreshold)
+				return true;
 
-				return false;
-			};
-			knownPeers.removeIf(notRecentlyConnected);
+			return false;
+		};
+		knownPeers.removeIf(notRecentlyConnected);
 
-			if (peer.getVersion() >= 2) {
-				List<PeerAddress> peerAddresses = new ArrayList<>();
+		if (peer.getVersion() >= 2) {
+			List<PeerAddress> peerAddresses = new ArrayList<>();
 
-				for (PeerData peerData : knownPeers) {
-					try {
-						InetAddress address = InetAddress.getByName(peerData.getAddress().getHost());
+			for (PeerData peerData : knownPeers) {
+				try {
+					InetAddress address = InetAddress.getByName(peerData.getAddress().getHost());
 
-						// Don't send 'local' addresses if peer is not 'local'. e.g. don't send localhost:9084 to node4.qortal.org
-						if (!peer.getIsLocal() && Peer.isAddressLocal(address))
-							continue;
+					// Don't send 'local' addresses if peer is not 'local'. e.g. don't send localhost:9084 to node4.qortal.org
+					if (!peer.getIsLocal() && Peer.isAddressLocal(address))
+						continue;
 
-						peerAddresses.add(peerData.getAddress());
-					} catch (UnknownHostException e) {
-						// Couldn't resolve hostname to IP address so discard
-					}
+					peerAddresses.add(peerData.getAddress());
+				} catch (UnknownHostException e) {
+					// Couldn't resolve hostname to IP address so discard
 				}
-
-				// New format PEERS_V2 message that supports hostnames, IPv6 and ports
-				return new PeersV2Message(peerAddresses);
-			} else {
-				// Map to socket addresses
-				List<InetAddress> peerAddresses = new ArrayList<>();
-
-				for (PeerData peerData : knownPeers) {
-					try {
-						// We have to resolve to literal IP address to check for IPv4-ness.
-						// This isn't great if hostnames have both IPv6 and IPv4 DNS entries.
-						InetAddress address = InetAddress.getByName(peerData.getAddress().getHost());
-
-						// Legacy PEERS message doesn't support IPv6
-						if (address instanceof Inet6Address)
-							continue;
-
-						// Don't send 'local' addresses if peer is not 'local'. e.g. don't send localhost:9084 to node4.qortal.org
-						if (!peer.getIsLocal() && !Peer.isAddressLocal(address))
-							continue;
-
-						peerAddresses.add(address);
-					} catch (UnknownHostException e) {
-						// Couldn't resolve hostname to IP address so discard
-					}
-				}
-
-				// Legacy PEERS message that only sends IPv4 addresses
-				return new PeersMessage(peerAddresses);
 			}
-		} catch (DataException e) {
-			LOGGER.error("Repository issue while building PEERS message", e);
-			return new PeersMessage(Collections.emptyList());
+
+			// New format PEERS_V2 message that supports hostnames, IPv6 and ports
+			return new PeersV2Message(peerAddresses);
+		} else {
+			// Map to socket addresses
+			List<InetAddress> peerAddresses = new ArrayList<>();
+
+			for (PeerData peerData : knownPeers) {
+				try {
+					// We have to resolve to literal IP address to check for IPv4-ness.
+					// This isn't great if hostnames have both IPv6 and IPv4 DNS entries.
+					InetAddress address = InetAddress.getByName(peerData.getAddress().getHost());
+
+					// Legacy PEERS message doesn't support IPv6
+					if (address instanceof Inet6Address)
+						continue;
+
+					// Don't send 'local' addresses if peer is not 'local'. e.g. don't send localhost:9084 to node4.qortal.org
+					if (!peer.getIsLocal() && !Peer.isAddressLocal(address))
+						continue;
+
+					peerAddresses.add(address);
+				} catch (UnknownHostException e) {
+					// Couldn't resolve hostname to IP address so discard
+				}
+			}
+
+			// Legacy PEERS message that only sends IPv4 addresses
+			return new PeersMessage(peerAddresses);
 		}
 	}
 
@@ -1077,26 +1017,38 @@ public class Network {
 	}
 
 	public boolean forgetPeer(PeerAddress peerAddress) throws DataException {
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			int numDeleted = repository.getNetworkRepository().delete(peerAddress);
-			repository.saveChanges();
+		int numDeleted;
 
-			disconnectPeer(peerAddress);
+		synchronized (this.allKnownPeers) {
+			this.allKnownPeers.removeIf(peerData -> peerData.getAddress().equals(peerAddress));
 
-			return numDeleted != 0;
+			try (final Repository repository = RepositoryManager.getRepository()) {
+				numDeleted = repository.getNetworkRepository().delete(peerAddress);
+				repository.saveChanges();
+			}
 		}
+
+		disconnectPeer(peerAddress);
+
+		return numDeleted != 0;
 	}
 
 	public int forgetAllPeers() throws DataException {
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			int numDeleted = repository.getNetworkRepository().deleteAllPeers();
-			repository.saveChanges();
+		int numDeleted;
 
-			for (Peer peer : this.getConnectedPeers())
-				peer.disconnect("to be forgotten");
+		synchronized (this.allKnownPeers) {
+			this.allKnownPeers.clear();
 
-			return numDeleted;
+			try (final Repository repository = RepositoryManager.getRepository()) {
+				numDeleted = repository.getNetworkRepository().deleteAllPeers();
+				repository.saveChanges();
+			}
 		}
+
+		for (Peer peer : this.getConnectedPeers())
+			peer.disconnect("to be forgotten");
+
+		return numDeleted;
 	}
 
 	private void disconnectPeer(PeerAddress peerAddress) {
@@ -1116,7 +1068,72 @@ public class Network {
 
 	// Network-wide calls
 
-	private void mergePeers(String addedBy, List<PeerAddress> peerAddresses) {
+	public void prunePeers() throws DataException {
+		final Long now = NTP.getTime();
+		if (now == null)
+			return;
+
+		// Disconnect peers that are stuck during handshake
+		List<Peer> handshakePeers = this.getConnectedPeers();
+
+		// Disregard peers that have completed handshake or only connected recently
+		handshakePeers.removeIf(peer -> peer.getHandshakeStatus() == Handshake.COMPLETED || peer.getConnectionTimestamp() == null || peer.getConnectionTimestamp() > now - HANDSHAKE_TIMEOUT);
+
+		for (Peer peer : handshakePeers)
+			peer.disconnect(String.format("handshake timeout at %s", peer.getHandshakeStatus().name()));
+
+		// Prune 'old' peers from repository...
+		// Pruning peers isn't critical so no need to block for a repository instance.
+		try (final Repository repository = RepositoryManager.tryRepository()) {
+			if (repository == null)
+				return;
+
+			synchronized (this.allKnownPeers) {
+				// Fetch all known peers
+				List<PeerData> peers = new ArrayList<>(this.allKnownPeers);
+
+				// 'Old' peers:
+				// We attempted to connect within the last day
+				// but we last managed to connect over a week ago.
+				Predicate<PeerData> isNotOldPeer = peerData -> {
+					if (peerData.getLastAttempted() == null || peerData.getLastAttempted() < now - OLD_PEER_ATTEMPTED_PERIOD)
+						return true;
+
+					if (peerData.getLastConnected() == null || peerData.getLastConnected() > now - OLD_PEER_CONNECTION_PERIOD)
+						return true;
+
+					return false;
+				};
+
+				// Disregard peers that are NOT 'old'
+				peers.removeIf(isNotOldPeer);
+
+				// Don't consider already connected peers (simple address match)
+				synchronized (this.connectedPeers) {
+					peers.removeIf(isConnectedPeer);
+				}
+
+				for (PeerData peerData : peers) {
+					LOGGER.debug(() -> String.format("Deleting old peer %s from repository", peerData.getAddress().toString()));
+					repository.getNetworkRepository().delete(peerData.getAddress());
+				}
+
+				repository.saveChanges();
+			}
+		}
+	}
+
+	public void mergePeers(String addedBy, long addedWhen, List<PeerAddress> peerAddresses) throws DataException {
+		mergePeersLock.lock();
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			this.mergePeers(repository, addedBy, addedWhen, peerAddresses);
+		} finally {
+			mergePeersLock.unlock();
+		}
+	}
+
+	private void opportunisticMergePeers(String addedBy, List<PeerAddress> peerAddresses) {
 		final Long addedWhen = NTP.getTime();
 		if (addedWhen == null)
 			return;
@@ -1131,27 +1148,42 @@ public class Network {
 				if (repository == null)
 					return;
 
-				List<PeerData> knownPeers = repository.getNetworkRepository().getAllPeers();
+				this.mergePeers(repository, addedBy, addedWhen, peerAddresses);
 
-				// Filter out duplicates
-				Predicate<PeerAddress> isKnownAddress = peerAddress -> knownPeers.stream().anyMatch(knownPeerData -> knownPeerData.getAddress().equals(peerAddress));
+			} catch (DataException e) {
+				// Already logged by this.mergePeers()
+			}
+		} finally {
+			mergePeersLock.unlock();
+		}
+	}
+
+	private void mergePeers(Repository repository, String addedBy, long addedWhen, List<PeerAddress> peerAddresses) throws DataException {
+		List<PeerData> newPeers;
+		synchronized (this.allKnownPeers) {
+			for (PeerData knownPeerData : this.allKnownPeers) {
+				// Filter out duplicates, without resolving via DNS
+				Predicate<PeerAddress> isKnownAddress = peerAddress -> knownPeerData.getAddress().equals(peerAddress);
 				peerAddresses.removeIf(isKnownAddress);
+			}
 
-				repository.discardChanges();
+			// Add leftover peer addresses to known peers list
+			newPeers = peerAddresses.stream().map(peerAddress -> new PeerData(peerAddress, addedWhen, addedBy)).collect(Collectors.toList());
 
-				// Save the rest into database
-				for (PeerAddress peerAddress : peerAddresses) {
-					PeerData peerData = new PeerData(peerAddress, addedWhen, addedBy);
-					LOGGER.info(String.format("Adding new peer %s to repository", peerAddress));
+			this.allKnownPeers.addAll(newPeers);
+
+			try {
+				// Save new peers into database
+				for (PeerData peerData : newPeers) {
+					LOGGER.info(String.format("Adding new peer %s to repository", peerData.getAddress()));
 					repository.getNetworkRepository().save(peerData);
 				}
 
 				repository.saveChanges();
 			} catch (DataException e) {
-				LOGGER.error("Repository issue while merging peers list from remote node", e);
+				LOGGER.error(String.format("Repository issue while merging peers list from %s", addedBy), e);
+				throw e;
 			}
-		} finally {
-			mergePeersLock.unlock();
 		}
 	}
 

src/main/java/org/qortal/network/Peer.java

@@ -7,6 +7,8 @@ import java.net.SocketTimeoutException;
 import java.net.StandardSocketOptions;
 import java.net.UnknownHostException;
 import java.nio.ByteBuffer;
+import java.nio.channels.SelectionKey;
+import java.nio.channels.Selector;
 import java.nio.channels.SocketChannel;
 import java.security.SecureRandom;
 import java.util.Collections;
@@ -108,10 +110,10 @@ public class Peer {
 	}
 
 	/** Construct Peer using existing, connected socket */
-	public Peer(SocketChannel socketChannel) throws IOException {
+	public Peer(SocketChannel socketChannel, Selector channelSelector) throws IOException {
 		this.isOutbound = false;
 		this.socketChannel = socketChannel;
-		sharedSetup();
+		sharedSetup(channelSelector);
 
 		this.resolvedAddress = ((InetSocketAddress) socketChannel.socket().getRemoteSocketAddress());
 		this.isLocal = isAddressLocal(this.resolvedAddress.getAddress());
@@ -254,17 +256,18 @@ public class Peer {
 		new SecureRandom().nextBytes(verificationCodeExpected);
 	}
 
-	private void sharedSetup() throws IOException {
+	private void sharedSetup(Selector channelSelector) throws IOException {
 		this.connectionTimestamp = NTP.getTime();
 		this.socketChannel.setOption(StandardSocketOptions.TCP_NODELAY, true);
 		this.socketChannel.configureBlocking(false);
+		this.socketChannel.register(channelSelector, SelectionKey.OP_READ);
 		this.byteBuffer = null; // Defer allocation to when we need it, to save memory. Sorry GC!
 		this.replyQueues = Collections.synchronizedMap(new HashMap<Integer, BlockingQueue<Message>>());
 		this.pendingMessages = new LinkedBlockingQueue<>();
 	}
 
-	public SocketChannel connect() {
-		LOGGER.trace(String.format("Connecting to peer %s", this));
+	public SocketChannel connect(Selector channelSelector) {
+		LOGGER.trace(() -> String.format("Connecting to peer %s", this));
 
 		try {
 			this.resolvedAddress = this.peerData.getAddress().toSocketAddress();
@@ -272,10 +275,6 @@ public class Peer {
 
 			this.socketChannel = SocketChannel.open();
 			this.socketChannel.socket().connect(resolvedAddress, CONNECT_TIMEOUT);
-
-			LOGGER.debug(String.format("Connected to peer %s", this));
-			sharedSetup();
-			return socketChannel;
 		} catch (SocketTimeoutException e) {
 			LOGGER.trace(String.format("Connection timed out to peer %s", this));
 			return null;
@@ -286,6 +285,20 @@ public class Peer {
 			LOGGER.trace(String.format("Connection failed to peer %s", this));
 			return null;
 		}
+
+		try {
+			LOGGER.debug(() -> String.format("Connected to peer %s", this));
+			sharedSetup(channelSelector);
+			return socketChannel;
+		} catch (IOException e) {
+			LOGGER.trace(String.format("Post-connection setup failed, peer %s", this));
+			try {
+				socketChannel.close();
+			} catch (IOException ce) {
+				// Failed to close?
+			}
+			return null;
+		}
 	}
 
 	/**

src/main/java/org/qortal/utils/ExecuteProduceConsume.java

@@ -30,7 +30,7 @@ public abstract class ExecuteProduceConsume implements Runnable {
 	private final Logger logger;
 	private final boolean isLoggerTraceEnabled;
 
-	private ExecutorService executor;
+	protected ExecutorService executor;
 
 	// These are volatile to prevent thread-local caching of values
 	// but all are updated inside synchronized blocks
@@ -85,6 +85,10 @@ public abstract class ExecuteProduceConsume implements Runnable {
 		return snapshot;
 	}
 
+	protected void onSpawnFailure() {
+		/* Allow override in subclasses */
+	}
+
 	/**
 	 * Returns a Task to be performed, possibly blocking.
 	 * 
@@ -180,6 +184,7 @@ public abstract class ExecuteProduceConsume implements Runnable {
 							++this.spawnFailures;
 							this.hasThreadPending = false;
 							this.logger.trace(() -> String.format("[%d] failed to spawn another thread", Thread.currentThread().getId()));
+							this.onSpawnFailure();
 						}
 					} else {
 						this.logger.trace(() -> String.format("[%d] NOT spawning another thread", Thread.currentThread().getId()));

src/main/java/org/qortal/utils/ExecutorDumper.java

@@ -0,0 +1,81 @@
+package org.qortal.utils;
+
+import java.lang.reflect.Field;
+import java.util.HashSet;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.locks.ReentrantLock;
+
+public abstract class ExecutorDumper {
+
+	private static final String OUR_CLASS_NAME = ExecutorDumper.class.getName();
+
+	public static void dump(ExecutorService executor, int checkDepth, Class<?> skipClass) {
+		if (executor instanceof ThreadPoolExecutor)
+			dumpThreadPoolExecutor((ThreadPoolExecutor) executor, checkDepth, skipClass);
+
+		return;
+	}
+
+	private static void dumpThreadPoolExecutor(ThreadPoolExecutor executor, int checkDepth, Class<?> skipClass) {
+		try {
+			Field mainLockField = executor.getClass().getDeclaredField("mainLock");
+			mainLockField.setAccessible(true);
+
+			Field workersField = executor.getClass().getDeclaredField("workers");
+			workersField.setAccessible(true);
+
+			Class<?>[] declaredClasses = executor.getClass().getDeclaredClasses();
+
+			Class<?> workerClass = null;
+			for (int i = 0; i < declaredClasses.length; ++i)
+				if (declaredClasses[i].getSimpleName().equals("Worker")) {
+					workerClass = declaredClasses[i];
+					break;
+				}
+
+			if (workerClass == null)
+				return;
+
+			Field workerThreadField = workerClass.getDeclaredField("thread");
+			workerThreadField.setAccessible(true);
+
+			String skipClassName = skipClass.getName();
+
+			ReentrantLock mainLock = (ReentrantLock) mainLockField.get(executor);
+			mainLock.lock();
+
+			try {
+				@SuppressWarnings("unchecked")
+				HashSet<Object> workers = (HashSet<Object>) workersField.get(executor);
+
+				WORKER_LOOP:
+				for (Object workerObj : workers) {
+					Thread thread = (Thread) workerThreadField.get(workerObj);
+
+					StackTraceElement[] stackTrace = thread.getStackTrace();
+					if (stackTrace.length == 0)
+						continue;
+
+					for (int d = 0; d < checkDepth; ++d) {
+						String stackClassName = stackTrace[d].getClassName();
+						if (stackClassName.equals(skipClassName) || stackClassName.equals(OUR_CLASS_NAME))
+							continue WORKER_LOOP;
+					}
+
+					System.out.println(String.format("[%d] %s:", thread.getId(), thread.getName()));
+
+					for (int d = 0; d < stackTrace.length; ++d)
+						System.out.println(String.format("\t\t%s.%s at %s:%d",
+							stackTrace[d].getClassName(), stackTrace[d].getMethodName(),
+							stackTrace[d].getFileName(), stackTrace[d].getLineNumber()));
+				}
+			} finally {
+				mainLock.unlock();
+			}
+		} catch (Exception e) {
+			//
+		}
+	}
+
+}