Lock mysql table with php

Question

Script 1.

$query_ = \"lock tables test1 as test11 write\";
mysql_query($query);
$query_ = \"select * from test11\";
sleep(20);
$query_ = \"unlock tables\";
m         


        

Answer 1

If you do not want others to access that table then use

LOCK TABLES test1 WRITE;

Other script will not return error but will wait until lock is released.

Hope it helps...

Answer 2

You have to grant the rights of lock tables to the db user.

Answer 3

You are read locking the table with $query_ = "lock tables test1 as test11 read";- which means that other queries can still read it without any problems what-so-ever (Relevant link - scroll down to the section on lock types):

Info on the read lock type:

• The session that holds the lock can read the table (but not write it).
• Multiple sessions can acquire a READ lock for the table at the same time.
• Other sessions can read the table without explicitly acquiring a READ lock.

If you want to stop anything else so much as reding the table, you need to use a write lock as follows:

$query_ = "lock tables test1 as test11 write";

Answer 4

You have a misconception about what locks do. Locks to do not prevent other scripts from accessing data, instead locks affect the timing of when other scripts will access the data. When script 2 tries to access or modify data that it is not allowed to because of a lock, it will pause and wait for the lock to be released. After script 1 unlocks the table, script 2 will proceed and complete without any problems.