Added maxTransactionsPerBlock setting (default 25) to reduce minting load on slower machines.

This is a short term limit, is well above current usage levels, and can be increased substantially in future once the block minter code has been improved.

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

@@ -314,7 +314,7 @@ public interface TransactionRepository {
 	 * @return list of transactions, or empty if none.
 	 * @throws DataException
 	 */
-	public List<TransactionData> getUnconfirmedTransactions(EnumSet<TransactionType> excludedTxTypes) throws DataException;
+	public List<TransactionData> getUnconfirmedTransactions(EnumSet<TransactionType> excludedTxTypes, Integer limit) throws DataException;
 
 	/**
 	 * Remove transaction from unconfirmed transactions pile.

src/main/java/org/qortal/repository/hsqldb/transaction/HSQLDBTransactionRepository.java

@@ -1429,8 +1429,10 @@ public class HSQLDBTransactionRepository implements TransactionRepository {
 	}
 
 	@Override
-	public List<TransactionData> getUnconfirmedTransactions(EnumSet<TransactionType> excludedTxTypes) throws DataException {
+	public List<TransactionData> getUnconfirmedTransactions(EnumSet<TransactionType> excludedTxTypes, Integer limit) throws DataException {
 		StringBuilder sql = new StringBuilder(1024);
+		List<Object> bindParams = new ArrayList<>();
+
 		sql.append("SELECT signature FROM UnconfirmedTransactions ");
 		sql.append("JOIN Transactions USING (signature) ");
 		sql.append("WHERE type NOT IN (");
@@ -1446,12 +1448,17 @@ public class HSQLDBTransactionRepository implements TransactionRepository {
 		}
 
 		sql.append(")");
-		sql.append("ORDER BY created_when, signature");
+		sql.append("ORDER BY created_when, signature ");
+
+		if (limit != null) {
+			sql.append("LIMIT ?");
+			bindParams.add(limit);
+		}
 
 		List<TransactionData> transactions = new ArrayList<>();
 
 		// Find transactions with no corresponding row in BlockTransactions
-		try (ResultSet resultSet = this.repository.checkedExecute(sql.toString())) {
+		try (ResultSet resultSet = this.repository.checkedExecute(sql.toString(), bindParams.toArray())) {
 			if (resultSet == null)
 				return transactions;
 

src/main/java/org/qortal/settings/Settings.java

@@ -146,6 +146,9 @@ public class Settings {
 	/* How many blocks to cache locally. Defaulted to 10, which covers a typical Synchronizer request + a few spare */
 	private int blockCacheSize = 10;
 
+	/** Maximum number of transactions for the block minter to include in a block */
+	private int maxTransactionsPerBlock = 25;
+
 	/** How long to keep old, full, AT state data (ms). */
 	private long atStatesMaxLifetime = 5 * 24 * 60 * 60 * 1000L; // milliseconds
 	/** How often to attempt AT state trimming (ms). */
@@ -693,6 +696,10 @@ public class Settings {
 		return this.blockCacheSize;
 	}
 
+	public int getMaxTransactionsPerBlock() {
+		return this.maxTransactionsPerBlock;
+	}
+
 	public boolean isTestNet() {
 		return this.isTestNet;
 	}

src/main/java/org/qortal/transaction/Transaction.java

@@ -641,7 +641,8 @@ public abstract class Transaction {
 		BlockData latestBlockData = repository.getBlockRepository().getLastBlock();
 
 		EnumSet<TransactionType> excludedTxTypes = EnumSet.of(TransactionType.CHAT, TransactionType.PRESENCE);
-		List<TransactionData> unconfirmedTransactions = repository.getTransactionRepository().getUnconfirmedTransactions(excludedTxTypes);
+		int limit = Settings.getInstance().getMaxTransactionsPerBlock();
+		List<TransactionData> unconfirmedTransactions = repository.getTransactionRepository().getUnconfirmedTransactions(excludedTxTypes, limit);
 
 		unconfirmedTransactions.sort(getDataComparator());