Major CPU optimization to block minter

Load sorted list of reward share public keys into memory, so that the indexes can be obtained. This is around 100x faster than querying each index separately (and the savings will increase as more keys are added).

For 4150 reward share keys, it was taking around 5000ms to query individually, vs 50ms using this approach.

The main trade off is that these 4150 keys require around 130kB of additional memory when minting (and this will increase proportionally with more minters). However, this one query was often accounting for 50% of the entire core's CPU usage, so the additional memory usage seems insignificant by comparison.

To gain confidence, I ran both old and new approaches side by side, and confirmed that the indexes matched exactly.

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

@@ -8,13 +8,7 @@ import java.math.BigInteger;
 import java.math.RoundingMode;
 import java.text.DecimalFormat;
 import java.text.NumberFormat;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
+import java.util.*;
 import java.util.stream.Collectors;
 
 import org.apache.logging.log4j.Level;
@@ -333,6 +327,11 @@ public class Block {
 				onlineAccountsTimestamp = onlineAccountData.getTimestamp();
 		}
 
+		// Load sorted list of reward share public keys into memory, so that the indexes can be obtained.
+		// This is up to 100x faster than querying each index separately. For 4150 reward share keys, it
+		// was taking around 5000ms to query individually, vs 50ms using this approach.
+		List<byte[]> allRewardSharePublicKeys = repository.getAccountRepository().getRewardSharePublicKeys();
+
 		// Map using index into sorted list of reward-shares as key
 		Map<Integer, OnlineAccountData> indexedOnlineAccounts = new HashMap<>();
 		for (OnlineAccountData onlineAccountData : onlineAccounts) {
@@ -340,10 +339,7 @@ public class Block {
 			if (onlineAccountData.getTimestamp() != onlineAccountsTimestamp)
 				continue;
 
-			Integer accountIndex = repository.getAccountRepository().getRewardShareIndex(onlineAccountData.getPublicKey());
-			if (accountIndex == null)
-				// Online account (reward-share) with current timestamp but reward-share cancelled
-				continue;
+			Integer accountIndex = getRewardShareIndex(onlineAccountData.getPublicKey(), allRewardSharePublicKeys);
 
 			indexedOnlineAccounts.put(accountIndex, onlineAccountData);
 		}
@@ -2029,6 +2025,26 @@ public class Block {
 		this.repository.getAccountRepository().tidy();
 	}
 
+	// Utils
+
+	/**
+	 * Find index of rewardSharePublicKey in list of rewardSharePublicKeys
+	 *
+	 * @param rewardSharePublicKey - the key to query
+	 * @param rewardSharePublicKeys - a sorted list of keys
+	 * @return - the index of the key, or null if not found
+	 */
+	private static Integer getRewardShareIndex(byte[] rewardSharePublicKey, List<byte[]> rewardSharePublicKeys) {
+		int index = 0;
+		for (byte[] publicKey : rewardSharePublicKeys) {
+			if (Arrays.equals(rewardSharePublicKey, publicKey)) {
+				return index;
+			}
+			index++;
+		}
+		return null;
+	}
+
 	private void logDebugInfo() {
 		try {
 			// Avoid calculations if possible. We have to check against INFO here, since Level.isMoreSpecificThan() confusingly uses <= rather than just <

src/main/java/org/qortal/repository/AccountRepository.java

@@ -149,6 +149,8 @@ public interface AccountRepository {
 
 	public RewardShareData getRewardShare(byte[] rewardSharePublicKey) throws DataException;
 
+	public List<byte[]> getRewardSharePublicKeys() throws DataException;
+
 	public boolean isRewardSharePublicKey(byte[] publicKey) throws DataException;
 
 	/** Returns number of active reward-shares involving passed public key as the minting account only. */

src/main/java/org/qortal/repository/hsqldb/HSQLDBAccountRepository.java

@@ -633,6 +633,27 @@ public class HSQLDBAccountRepository implements AccountRepository {
 		}
 	}
 
+	@Override
+	public List<byte[]> getRewardSharePublicKeys() throws DataException {
+		String sql = "SELECT reward_share_public_key FROM RewardShares ORDER BY reward_share_public_key";
+
+		List<byte[]> rewardSharePublicKeys = new ArrayList<>();
+
+		try (ResultSet resultSet = this.repository.checkedExecute(sql)) {
+			if (resultSet == null)
+				return null;
+
+			do {
+				byte[] rewardSharePublicKey = resultSet.getBytes(1);
+				rewardSharePublicKeys.add(rewardSharePublicKey);
+			} while (resultSet.next());
+
+			return rewardSharePublicKeys;
+		} catch (SQLException e) {
+			throw new DataException("Unable to fetch reward-share public keys from repository", e);
+		}
+	}
+
 	@Override
 	public boolean isRewardSharePublicKey(byte[] publicKey) throws DataException {
 		try {