我对mysql事物隔离性一向是一知半解,这次还是下决心做了一个测试,不过测试的结果无法解释
求大神指教:
主函数如下:
public static void main(String args[]) {
// 初始化数据库
String dev = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/testdb?relaxAutoCommit=true&zeroDateTimeBehavior=convertToNull&characterEncoding=utf8";
String user = "root";
String pwd = "123456";
DBCPOper oper = new DBCPOper();
// SimpleDbOper oper = new SimpleDbOper();
oper.initDB(dev, url, user, pwd);
COMMDB.initDB(oper);
System.out.println("begin db...");
Thread t = new Thread(new AddDba());
t.start();
t = new Thread(new AddDbb());
t.start();
}
private static class AddDba implements Runnable {
@Override
public void run() {
try {
TransDBOper trans = null;
trans = COMMDB.getDBTrances();//这句话相当于打开一个事务,后面的那些操作只要是在同一个线程,那么用同一个事物
if (trans != null) {
System.out.println(Thread.currentThread().getName() + "|trans is open");
trans.setThreadTrans();
}
String sql = "update testdb set value = value + 1";
for (int i = 0; i < 1000; i++) {
System.out.println(Thread.currentThread().getName() + "("+i+")");
COMMDB.executeUpdate(sql);
}
if (trans != null) {
System.out.println(Thread.currentThread().getName() + "|trans is close");
TransDBOper.closeThreadTrans(true);//这个相当于关闭事务,并且commit
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
private static class AddDbb implements Runnable {
@Override
public void run() {
try {
TransDBOper trans = null;
trans = COMMDB.getDBTrances(); //代码相同,这个也是打开一个事物,在同一个线程中,将会用同一个事务
if (trans != null) {
System.out.println(Thread.currentThread().getName() + "|trans is open");
trans.setThreadTrans();
}
String sql = "update testdb set value = value + 1";
for (int i = 0; i < 1000; i++) {
System.out.println(Thread.currentThread().getName() + "("+i+")");
COMMDB.executeUpdate(sql);
}
if (trans != null) {
System.out.println(Thread.currentThread().getName() + "|trans is close");
TransDBOper.closeThreadTrans(true);//这个相当于关闭事务并commit
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
我想着这种情况下,数据库一定会因为事务脏数据问题而被写错。
但事实不是这样,而是好好的,数据库结果是正确的加了2000次
我检查一下打印结果,如下:
begin db...
Thread-0|trans is open
Thread-1|trans is open
Thread-1(0)
Thread-0(0)
Thread-0(1)
Thread-0(2)
Thread-0(3)
....
Thread-0(991)
Thread-0(992)
Thread-0(993)
Thread-0(994)
Thread-0(995)
Thread-0(996)
Thread-0(997)
Thread-0(998)
Thread-0(999)
Thread-0|trans is close
Thread-1(1)
Thread-1(2)
...
Thread-1(993)
Thread-1(994)
Thread-1(995)
Thread-1(996)
Thread-1(997)
Thread-1(998)
Thread-1(999)
Thread-1|trans is close
可见,我的程序是没有做同步的,但序号是如此的正确。跟做了同步的一样。
我猜猜是数据库一个事务里头对一个表做了更改,那么这个事务只要没结束,
其他事务会被暂时性的挂起。
我不清楚是否是这样,结合mysql的事务的四个事务隔离级别,求高手解释一下这个现象。