如何修复锁定等待超时？

Question

我正在使用glassfish 3.1.2和MySQL。运行我的应用程序时，我看到以下错误：

SEVERE: java.sql.SQLException: Lock wait timeout exceeded; try restarting transaction

下面的

是源代码：

 public synchronized long generateKey(String sequenceName,int count) throws Exception {

                 PreparedStatement stmt=null;
                 ResultSet rset=null;
                 Connection db_conn = null;
                 StringBuffer sql = new StringBuffer();
                 long key=-1;
                 long maxKeyCount;
                 String sqlSeqNum="";

                 try {

                  //     db_conn = Utility.getConnection("PASDataSource");
                         db_conn = Util.getConnection("ftpds");

                       sql.append("SELECT SEQ_NUM ");
                       sql.append("FROM SEQUENCE_GENERATOR ");
                       //SJ 2009.02.11, commented and added line below
                       //sql.append("WHERE sequence_name = ? ");
                        sql.append("WHERE SEQUENCE_NAME = ? for update");

                       System.out.println(sql + "::" + sequenceName);
                       stmt = db_conn.prepareStatement(sql.toString());

                       stmt.clearParameters();

                       stmt.setString(1,sequenceName);

                       rset = stmt.executeQuery ();

                        // Iterate through the result set
                        while(rset.next()) {
                              key =   rset.getInt(1);

                              // Update the key
                        }
                        rset.close();
                        stmt.close();
                        stmt = null;
                        rset = null;

                        if(key != -1) {

                              if((key + count) > MAX_KEY_COUNT) {
                                  // reset key count
                                  // key = 1;
                                  sqlSeqNum = "";
                              }
                              else
                                  sqlSeqNum = " seq_num + ";

                              sql = new StringBuffer();
                              sql.append("UPDATE SEQUENCE_GENERATOR SET SEQ_NUM = " + sqlSeqNum  + count );
                              sql.append(" WHERE SEQUENCE_NAME = ? ");
                              sql.append(" AND   SEQ_NUM = ? ");
                              stmt = db_conn.prepareStatement(sql.toString());

                              stmt.clearParameters();

                              stmt.setString(1,sequenceName);
                              stmt.setLong(2,key);

                              if(stmt.executeUpdate() != 1) {
                                   System.out.println(
                                               ":Not able to generate a new UNIQUE key for sequence :" + sequenceName);
                                   throw new Exception("Not able to generate a new UNIQUE key for sequence :" + sequenceName );
                              }
                              return key;
                        }

                        return -1;
                   }
                   catch (Exception e) {
                         System.out.println(e.getMessage());
                         throw e;
                   }
                 finally {
                     if(db_conn!=null){ 
                     db_conn.close();
                     System.out.println("Inside finally, generateKey(String sequenceName,int count) method");   
                 }}
       }

完整堆栈跟踪显示错误发生在rset = stmt.executeQuery ();。我第一次看到这个特殊的错误。如何解决这个问题？