Question

Let’s create Page.php

 query1
 query2
 query3

Is there any way to lock a few tables, so if one user visits Page.php and second user opens this page a little bit later, second user would need to wait until the first user’s all queries executes.

And more importantly, would it slow a website very much if there are a few hundreds users on the same page at the same time?

Thank you.

Answer 1

You can use row level locking to cause the connection to block for other users.

BEGIN TRAN

UPDATE table1 set locked = 1;  //table locks are only taken out when data is written, you could possibly also use lock hints.
UPDATE table2 set locked = 1;
UPDATE table3 set locked = 1;

//Tables are locked, do whatever you need here, other users hitting the page will block at the first update statement until this connection hits the commit or rollback

update table1 set locked = 0;
update table2 set locked = 0;
update table3 set locked = 0;

COMMIT

Note that a select statement never causes a lock on a row or table though you may be able to use locking hints to cause it to lock the row. Your best bet is to just touch the row by setting a value in the row to itself or adding another column.

Databases perform well because they accommodate concurrency. Any time you cause what would be concurrent to behave serially, you’ll incur a performance penalty. In some cases this may be okay, it really depends on what you’re actually doing with it.

I’m more of a SQL Server guy, but it’s pretty generic DBMS concepts, for further information I would look into:

Transaction Isolation Levels
http://dev.mysql.com/doc/refman/5.0/en/set-transaction.html

Locking Hints
http://www.xaprb.com/blog/2006/08/05/how-to-give-locking-hints-in-mysql/

Row / Table Locking Mechanisms
http://dev.mysql.com/doc/refman/5.5/en/internal-locking.html