Add more latest block caching to reduce repository accesses, especially for requests from remote peers

src/main/java/org/qortal/block/BlockChain.java

@@ -568,7 +568,7 @@ public class BlockChain {
 					orphanBlockData = repository.getBlockRepository().fromHeight(height);
 
 					repository.discardChanges(); // clear transaction status to prevent deadlocks
-					Controller.getInstance().onNewBlock(orphanBlockData);
+					Controller.getInstance().onOrphanedBlock(orphanBlockData);
 				}
 
 				return true;

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

@@ -16,6 +16,7 @@ import java.util.Collections;
 import java.util.Deque;
 import java.util.HashMap;
 import java.util.Iterator;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
@@ -24,6 +25,7 @@ import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.ReentrantLock;
+import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
@@ -135,7 +137,10 @@ public class Controller extends Thread {
 	private ExecutorService callbackExecutor = Executors.newFixedThreadPool(3);
 	private volatile boolean notifyGroupMembershipChange = false;
 
-	private volatile BlockData chainTip = null;
+	private static final int LATEST_BLOCKS_SIZE = 10; // To cover typical Synchronizer request + a few spare
+	/** Latest blocks on our chain. Note: tail/last is the latest block. */
+	private final Deque<BlockData> latestBlocks = new LinkedList<>();
+	private volatile BlockMessage latestBlockMessage = null;
 
 	private long repositoryBackupTimestamp = startTime; // ms
 	private long ntpCheckTimestamp = startTime; // ms
@@ -238,21 +243,36 @@ public class Controller extends Thread {
 
 	/** Returns current blockchain height, or 0 if it's not available. */
 	public int getChainHeight() {
-		BlockData blockData = this.chainTip;
-		if (blockData == null)
-			return 0;
+		synchronized (this.latestBlocks) {
+			BlockData blockData = this.latestBlocks.peekLast();
+			if (blockData == null)
+				return 0;
 
-		return blockData.getHeight();
+			return blockData.getHeight();
+		}
 	}
 
 	/** Returns highest block, or null if it's not available. */
 	public BlockData getChainTip() {
-		return this.chainTip;
+		synchronized (this.latestBlocks) {
+			return this.latestBlocks.peekLast();
+		}
 	}
 
-	/** Cache new blockchain tip. */
-	public void setChainTip(BlockData blockData) {
-		this.chainTip = blockData;
+	public void refillLatestBlocksCache() throws DataException {
+		// Set initial chain height/tip
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			BlockData blockData = repository.getBlockRepository().getLastBlock();
+
+			synchronized (this.latestBlocks) {
+				this.latestBlocks.clear();
+
+				for (int i = 0; i < LATEST_BLOCKS_SIZE && blockData != null; ++i) {
+					this.latestBlocks.addFirst(blockData);
+					blockData = repository.getBlockRepository().fromHeight(blockData.getHeight() - 1);
+				}
+			}
+		}
 	}
 
 	public ReentrantLock getBlockchainLock() {
@@ -334,13 +354,8 @@ public class Controller extends Thread {
 		try {
 			BlockChain.validate();
 
-			// Set initial chain height/tip
-			try (final Repository repository = RepositoryManager.getRepository()) {
-				BlockData blockData = repository.getBlockRepository().getLastBlock();
-
-				Controller.getInstance().setChainTip(blockData);
-				LOGGER.info(String.format("Our chain height at start-up: %d", blockData.getHeight()));
-			}
+			Controller.getInstance().refillLatestBlocksCache();
+			LOGGER.info(String.format("Our chain height at start-up: %d", Controller.getInstance().getChainHeight()));
 		} catch (DataException e) {
 			LOGGER.error("Couldn't validate blockchain", e);
 			Gui.getInstance().fatalError("Blockchain validation issue", e);
@@ -572,9 +587,10 @@ public class Controller extends Thread {
 
 	public SynchronizationResult actuallySynchronize(Peer peer, boolean force) throws InterruptedException {
 		boolean hasStatusChanged = false;
+		BlockData priorChainTip = this.getChainTip();
 
 		synchronized (this.syncLock) {
-			this.syncPercent = (this.chainTip.getHeight() * 100) / peer.getChainTipData().getLastHeight();
+			this.syncPercent = (priorChainTip.getHeight() * 100) / peer.getChainTipData().getLastHeight();
 
 			// Only update SysTray if we're potentially changing height
 			if (this.syncPercent < 100) {
@@ -586,8 +602,6 @@ public class Controller extends Thread {
 		if (hasStatusChanged)
 			updateSysTray();
 
-		BlockData priorChainTip = this.chainTip;
-
 		try {
 			SynchronizationResult syncResult = Synchronizer.getInstance().synchronize(peer, force);
 			switch (syncResult) {
@@ -850,11 +864,84 @@ public class Controller extends Thread {
 		// Protective copy
 		BlockData blockDataCopy = new BlockData(latestBlockData);
 
-		this.setChainTip(blockDataCopy);
+		synchronized (this.latestBlocks) {
+			BlockData cachedChainTip = this.latestBlocks.peekLast();
+
+			if (cachedChainTip != null && Arrays.equals(cachedChainTip.getSignature(), blockDataCopy.getReference())) {
+				// Chain tip is parent for new latest block, so we can safely add new latest block
+				this.latestBlocks.addLast(latestBlockData);
+			} else {
+				if (cachedChainTip != null)
+					// Chain tip didn't match - potentially abnormal behaviour?
+					LOGGER.debug(() -> String.format("Cached chain tip %.8s not parent for new latest block %.8s (reference %.8s)",
+							Base58.encode(cachedChainTip.getSignature()),
+							Base58.encode(blockDataCopy.getSignature()),
+							Base58.encode(blockDataCopy.getReference())));
+
+				// Protectively rebuild cache
+				try {
+					this.refillLatestBlocksCache();
+				} catch (DataException e) {
+					LOGGER.warn(() -> "Couldn't refill latest blocks cache?", e);
+				}
+			}
+		}
+
+		this.onNewOrOrphanedBlock(blockDataCopy, NewBlockEvent::new);
+	}
+
+	public static class OrphanedBlockEvent implements Event {
+		private final BlockData blockData;
+
+		public OrphanedBlockEvent(BlockData blockData) {
+			this.blockData = blockData;
+		}
+
+		public BlockData getBlockData() {
+			return this.blockData;
+		}
+	}
+
+	/**
+	 * Callback for when we've orphaned a block.
+	 * <p>
+	 * See <b>WARNING</b> for {@link EventBus#notify(Event)}
+	 * to prevent deadlocks.
+	 */
+	public void onOrphanedBlock(BlockData latestBlockData) {
+		// Protective copy
+		BlockData blockDataCopy = new BlockData(latestBlockData);
+
+		synchronized (this.latestBlocks) {
+			BlockData cachedChainTip = this.latestBlocks.pollLast();
+
+			if (cachedChainTip != null && Arrays.equals(cachedChainTip.getReference(), blockDataCopy.getSignature())) {
+				// Chain tip was parent for new latest block that has been orphaned, so we're good
+			} else {
+				if (cachedChainTip != null)
+					// Chain tip didn't match - potentially abnormal behaviour?
+					LOGGER.debug(() -> String.format("Cached chain tip %.8s (reference %.8s) was not parent for new latest block %.8s",
+							Base58.encode(cachedChainTip.getSignature()),
+							Base58.encode(cachedChainTip.getReference()),
+							Base58.encode(blockDataCopy.getSignature())));
+
+				// Protectively rebuild cache
+				try {
+					this.refillLatestBlocksCache();
+				} catch (DataException e) {
+					LOGGER.warn(() -> "Couldn't refill latest blocks cache?", e);
+				}
+			}
+		}
+
+		this.onNewOrOrphanedBlock(blockDataCopy, OrphanedBlockEvent::new);
+	}
+
+	private void onNewOrOrphanedBlock(BlockData blockDataCopy, Function<BlockData, Event> eventConstructor) {
 		requestSysTrayUpdate = true;
 
 		// Notify listeners, trade-bot, etc.
-		EventBus.INSTANCE.notify(new NewBlockEvent(blockDataCopy));
+		EventBus.INSTANCE.notify(eventConstructor.apply(blockDataCopy));
 
 		if (this.notifyGroupMembershipChange) {
 			this.notifyGroupMembershipChange = false;
@@ -955,8 +1042,21 @@ public class Controller extends Thread {
 		GetBlockMessage getBlockMessage = (GetBlockMessage) message;
 		byte[] signature = getBlockMessage.getSignature();
 
+		BlockMessage blockMessage = this.latestBlockMessage;
+
+		// Check cached latest block message
+		if (blockMessage != null && Arrays.equals(blockMessage.getBlockData().getSignature(), signature)) {
+			blockMessage.setId(message.getId());
+
+			if (!peer.sendMessage(blockMessage))
+				peer.disconnect("failed to send block");
+
+			return;
+		}
+
 		try (final Repository repository = RepositoryManager.getRepository()) {
 			BlockData blockData = repository.getBlockRepository().fromSignature(signature);
+
 			if (blockData == null) {
 				// We don't have this block
 
@@ -973,10 +1073,16 @@ public class Controller extends Thread {
 
 			Block block = new Block(repository, blockData);
 
-			Message blockMessage = new BlockMessage(block);
+			blockMessage = new BlockMessage(block);
 			blockMessage.setId(message.getId());
+
+			// This call also causes the other needed data to be pulled in from repository
 			if (!peer.sendMessage(blockMessage))
 				peer.disconnect("failed to send block");
+
+			// If request is for latest block, cache it
+			if (Arrays.equals(this.getChainTip().getSignature(), signature))
+				this.latestBlockMessage = blockMessage;
 		} catch (DataException e) {
 			LOGGER.error(String.format("Repository issue while send block %s to peer %s", Base58.encode(signature), peer), e);
 		}
@@ -1023,32 +1129,38 @@ public class Controller extends Thread {
 
 	private void onNetworkGetBlockSummariesMessage(Peer peer, Message message) {
 		GetBlockSummariesMessage getBlockSummariesMessage = (GetBlockSummariesMessage) message;
-		byte[] parentSignature = getBlockSummariesMessage.getParentSignature();
+		final byte[] parentSignature = getBlockSummariesMessage.getParentSignature();
 
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			List<BlockSummaryData> blockSummaries = new ArrayList<>();
+		List<BlockSummaryData> blockSummaries = new ArrayList<>();
 
-			int numberRequested = Math.min(Network.MAX_BLOCK_SUMMARIES_PER_REPLY, getBlockSummariesMessage.getNumberRequested());
+		// Attempt to serve from our cache of latest blocks
+		synchronized (this.latestBlocks) {
+			blockSummaries = this.latestBlocks.stream()
+					.dropWhile(cachedBlockData -> Arrays.equals(cachedBlockData.getSignature(), parentSignature))
+					.map(BlockSummaryData::new)
+					.collect(Collectors.toList());
+		}
+
+		if (blockSummaries.isEmpty())
+			try (final Repository repository = RepositoryManager.getRepository()) {
+				int numberRequested = Math.min(Network.MAX_BLOCK_SUMMARIES_PER_REPLY, getBlockSummariesMessage.getNumberRequested());
 
-			do {
 				BlockData blockData = repository.getBlockRepository().fromReference(parentSignature);
 
-				if (blockData == null)
-					// No more blocks to send to peer
-					break;
+				while (blockData != null && blockSummaries.size() < numberRequested) {
+					BlockSummaryData blockSummary = new BlockSummaryData(blockData);
+					blockSummaries.add(blockSummary);
 
-				BlockSummaryData blockSummary = new BlockSummaryData(blockData);
-				blockSummaries.add(blockSummary);
-				parentSignature = blockData.getSignature();
-			} while (blockSummaries.size() < numberRequested);
+					blockData = repository.getBlockRepository().fromReference(blockData.getSignature());
+				}
+			} catch (DataException e) {
+				LOGGER.error(String.format("Repository issue while sending block summaries after %s to peer %s", Base58.encode(parentSignature), peer), e);
+			}
 
-			Message blockSummariesMessage = new BlockSummariesMessage(blockSummaries);
-			blockSummariesMessage.setId(message.getId());
-			if (!peer.sendMessage(blockSummariesMessage))
-				peer.disconnect("failed to send block summaries");
-		} catch (DataException e) {
-			LOGGER.error(String.format("Repository issue while sending block summaries after %s to peer %s", Base58.encode(parentSignature), peer), e);
-		}
+		Message blockSummariesMessage = new BlockSummariesMessage(blockSummaries);
+		blockSummariesMessage.setId(message.getId());
+		if (!peer.sendMessage(blockSummariesMessage))
+			peer.disconnect("failed to send block summaries");
 	}
 
 	private void onNetworkGetSignaturesV2Message(Peer peer, Message message) {

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

@@ -412,7 +412,7 @@ public class Synchronizer {
 			orphanBlockData = repository.getBlockRepository().fromHeight(ourHeight);
 
 			repository.discardChanges(); // clear transaction status to prevent deadlocks
-			Controller.getInstance().onNewBlock(orphanBlockData);
+			Controller.getInstance().onOrphanedBlock(orphanBlockData);
 		}
 
 		LOGGER.debug(String.format("Orphaned blocks back to height %d, sig %.8s - applying new blocks from peer %s", commonBlockHeight, commonBlockSig58, peer));

src/main/java/org/qortal/network/message/BlockMessage.java

@@ -34,6 +34,7 @@ public class BlockMessage extends Message {
 		super(MessageType.BLOCK);
 
 		this.block = block;
+		this.blockData = block.getBlockData();
 		this.height = block.getBlockData().getHeight();
 	}