Question

I have a java app that runs on multiple computers and they all connect to the same MySQL database. I need transactions to make sure database is updated correctly.

I have a problem with releasing locks. Here is the code:

public boolean bookSeats(int numeroSala, Calendar dataOra, List<Posto> posti) {
    JDBConnection connection = JDBConnection.getDbConnection();
    Connection conn = connection.conn;
    java.sql.Date javaSqlDate = new java.sql.Date(dataOra.getTime().getTime());
    java.sql.Time javaSqlTime = new java.sql.Time(dataOra.getTime().getTime());

    try {
        conn.setAutoCommit(false);
        conn.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
    } catch (SQLException e) {
        e.printStackTrace();
    }

    try
    {
        Posto p = null;
        ListIterator<Posto> itr = posti.listIterator();
        PreparedStatement stmt = null;
        stmt = conn.prepareStatement(
            "INSERT INTO sala?_tickets " + 
            "(giornoSpettacolo, orarioSpettacolo, fila, posto) " + 
            "VALUES (?, ?, ?, ?)");

        stmt.setInt(1, numeroSala);
        while(itr.hasNext())
        {
            p = itr.next();
            stmt.setString(2, javaSqlDate.toString()); // giornoSpettacolo
            stmt.setString(3, javaSqlTime.toString()); // orarioSpettacolo
            stmt.setInt(4, p.getFila()); // fila
            stmt.setInt(5, p.getNumero()); // posto
            stmt.addBatch();
        }

        stmt.executeBatch();

        conn.commit();
        return true;
    }
    catch (SQLException e) {
        e.printStackTrace();
    }

    return false;
}

This method works fine but when I try to execute the this on another computer at the same time, I get a DEADLOCK error even though the conn.commit() was completed.

As soon as I close the first application, the other application can run the method without Deadlock error. It seems like the COMMIT doesn’t release the lock?

Answer 1

Per MySQL documentation, about SERIALIZABLE:

This level is like REPEATABLE READ, but InnoDB implicitly converts all
plain SELECT statements to SELECT … LOCK IN SHARE MODE if autocommit
is disabled.

You might want to try re-enabled auto-commit after your commit, or try Connection. REPEATABLE_READ instead.