java - 超过锁定等待超时；尝试使用 JDBC 重新启动事务

Question

我有一个名为 Student 的 MySQL 表，其中包含两列 Student_id 和 name。

我使用两个连接对象触发两个查询，它给了我一个异常:

Exception in thread "main" java.sql.SQLException: Lock wait timeout 
exceeded; try restarting transaction
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1074)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4074)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4006)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2468)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2629)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2713)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2663)
    at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:888)
    at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:730)
    at jdbc.ConnectUsingJdbc.main(ConnectUsingJdbc.java:19)

这是产生错误的代码:

package jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class ConnectUsingJdbc {

    public static void main(String[] args) 
        throws ClassNotFoundException, SQLException{

        Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection(
            "jdbc:mysql://localhost:3306/test","root","root");
        Connection connection1 = DriverManager.getConnection(
            "jdbc:mysql://localhost:3306/test","root","root");
        connection.setAutoCommit(false);
        connection1.setAutoCommit(false);
        Statement statement = connection.createStatement();
        statement.execute("insert into student values (3,'kamal')");
        Statement statement1 = connection1.createStatement();
        statement1.execute("delete from student where student_id = 3");
        connection.commit();
        connection1.commit();
    }
}

我正在尝试使用我使用其他 connection 对象插入的 connection1 对象删除行。

为什么会出现此错误？

Answer 1

修改您的代码并对执行重新排序，如下所示。它应该工作正常:

Statement statement = connection.createStatement();
statement.execute("insert into student values (3,'kamal')");
connection.commit();

Statement statement1 = connection1.createStatement();
statement1.execute("delete from student where student_id = 3");
connection1.commit();

问题是，当您尝试执行新的删除语句时，先前执行的插入语句尚未提交并持有表上的锁，从而在数据库中造成死锁情况。