U14

import java.math.BigDecimal;
import java.sql.*;

public class Main {
    public static void main(String[] args) throws SQLException {
        initializeTable();
        TranA a = new TranA();
        TranB b = new TranB();
        a.start();
        b.start();
    }
    private static void initializeTable() throws SQLException {
        Connection c = DbContext.getConnectionA();
        c.setAutoCommit(true);
        Statement s = c.createStatement();
        s.execute("DROP TABLE IF EXISTS datas");
        System.out.println("wtf");
        s.execute("CREATE TABLE datas (type integer, value numeric)");
        s.execute("INSERT INTO datas VALUES (1, 10), (1, 20), (2, 100), (2,200)");
        s.close();
        c.setAutoCommit(false);
    }
}

class DbContext {
    public static Connection connectionA;
    public static Connection connectionB;

    public static Connection getConnectionA() throws SQLException {
        if (connectionA == null) {
            connectionA = DriverManager.getConnection(
                    "jdbc:postgresql://db.dai.fmph.uniba.sk/playground",
                    "gajdosech2@uniba.sk",
                    "datakyseliny");
            connectionA.setAutoCommit(false);
        }
        return connectionA;
    }

    public static Connection getConnectionB() throws SQLException {
        if (connectionB == null) {
            connectionB = DriverManager.getConnection(
                    "jdbc:postgresql://db.dai.fmph.uniba.sk/playground",
                    "gajdosech2@uniba.sk",
                    "datakyseliny");
            connectionB.setAutoCommit(false);
        }
        return connectionB;
    }
}

class TranB extends Thread {
    int count = 0;
    int countInserts = 0;
    int serializationErrorCounts = 0;

    @Override
    public void run() {
        while (countInserts < 1000) {
            count++;
            System.out.println("B");
            try {
                Connection c = DbContext.getConnectionB();
                c.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
                Statement s = c.createStatement();
                ResultSet r = s.executeQuery("SELECT SUM(value)::NUMERIC AS y FROM datas WHERE type = 2");
                r.next();
                BigDecimal y = r.getBigDecimal("y");
                s.execute("INSERT INTO datas (type,value) VALUES (1," + y + ")");
                c.commit();
                countInserts++;
            } catch (SQLException e) {
                if (e.getSQLState().equals("40001"))
                    serializationErrorCounts++;
                e.printStackTrace();
            }
        }
        System.out.println("Transaction B has run totally: " + count + " times");
        System.out.println("Transaction B had " + serializationErrorCounts + " serialization errors");
    }
}

class TranA extends Thread {
    int count = 0;
    int countInserts = 0;
    int serializationErrorCounts = 0;

    @Override
    public void run() {
        while (countInserts < 1000) {
            count++;
            System.out.println("A");
            try {
                Connection c = DbContext.getConnectionA();
                c.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
                Statement s = c.createStatement();
                ResultSet r = s.executeQuery("SELECT SUM(value)::NUMERIC AS x FROM datas WHERE type = 1");
                r.next();
                BigDecimal x = r.getBigDecimal("x");
                s.execute("INSERT INTO datas (type,value) VALUES (2," + x + ")");
                c.commit();
                countInserts++;
            } catch (SQLException e) {
                if (e.getSQLState().equals("40001"))
                    serializationErrorCounts++;
                e.printStackTrace();
            }
        }
        System.out.println("Transaction A has run totally: " + count + " times");
        System.out.println("Transaction A had " + serializationErrorCounts + " serialization errors");
    }
}