update locking behavior

[Joiyce]

Hello there,
My table
mysql> Show create Table City\G
*************************** 1. row ***************************
Table: City
Create Table: CREATE TABLE `City` (
`ID` int(11) NOT NULL,
`Name` char(35) NOT NULL default '',
`CountryCode` char(3) NOT NULL default '',
`District` char(20) NOT NULL default '',
`Population` int(11) NOT NULL default '0',
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1



mysql> show variables like 'tx%';
+---------------+-----------------+
| Variable_name | Value |
+---------------+-----------------+
| tx_isolation | REPEATABLE-READ |
+---------------+-----------------+
client 1

mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)

select * from City where ID>4050 for update;

+------+------------------+-------------+-------- -- This message may have been cut off and the rest will only be shown to members. To become a member, click here --

[Beau]

The 2nd Select is considered as a non-blocking read. Read a historical version of the data with SELECT except with Serializable isolation level. The Select will do a Read lock or shared lock on the selected rows. With a FOR UPDATE, another connection cannot write to the rows and cannot get a lock on the rows, but read without locking is always possible. -- This message may have been cut off and the rest will only be shown to members. To become a member, click here --