试验1

事务1：

#!/usr/bin/python

import time

import MySQLdb;

conn = MySQLdb.connect(host="localhost",port=3306,user="root",passwd="asdf",db="test",unix_socket="/data/mysql_3306/mysql.sock")

cursor = conn.cursor()

cursor.execute("select * from test")

while str!="1":

str = raw_input()

cursor.execute("update test id=id-1")

while str!="exit":

str = raw_input()

cursor.close()

conn.close()

在mysql命令行中输入以下：

mysql> select * from test;

当事务1中等待输入1时，显示出select匹配的行

当事务1中输入1时，显示结果如下：

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

结论：当select时会检测当前是否有事务会修改(比影响要确切一些)当前的记录时，才会被阻塞。

试验2

在事务1：

#!/usr/bin/python

import time

import MySQLdb;

conn = MySQLdb.connect(host="localhost",port=3306,user="root",passwd="asdf",db="test",unix_socket="/data/mysql_3306/mysql.sock")

cursor = conn.cursor()

cursor.execute("select * from test lock in share mode")

while str!="exit":

str = raw_input()

cursor.close()

conn.close()

在mysql命令行中输入以下：

mysql> update test set id=id-1;

ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

结论：当事务中包含select ...lock in share mode的时候，相关记录将会被锁住，不允许进行修改。

试验3

执行下面的python脚本两遍，并且同时输入1，2之后

#!/usr/bin/python

import time

import MySQLdb;

conn = MySQLdb.connect(host="localhost",port=3306,user="root",passwd="asdf",db="test",unix_socket="/data/mysql_3306/mysql.sock")

cursor = conn.cursor()

cursor.execute("select * from test lock in share mode")

str = ""

while str!="1":

str = raw_input()

while str!="2":

str = raw_input()

cursor.execute("update test set id=id-1")

while str!="exit":

str = raw_input()

cursor.close()

conn.close()

[root@TJSJHL196-139 tmp]# python test_transaction.py

1

2

Traceback (most recent call la