问题描述
- mysql事物隔离的问题,求大神指教
- 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。
解决方案
mysql的事务是可重复读的隔离级别 同时通过mvcc来防止幻读
时间: 2024-09-11 22:05:12