MySQL InnoDB dead lock on SELECT with exclusive lock (FOR UPDATE)

Question

I do this to ensure only once instance of this process is running (pseudo code php/mysql innodb):

START TRANSACTION
$rpid = SELECT `value` FROM locks WHERE n         


        

Answer 1

Without seeing the actual PHP code, it's hard to be sure - but is it possible that you are not actually using the same database connection between running the SELECT and the INSERT?

I typically prefer not to use transactions if I can avoid it; your problem could be solved by creating a single database query along the lines of

insert into locks
select ('lockname', $pid)
from locks
where name not in
(select name from locks)

By accessing the rows affected, you can see if the process is already running...