How to detect deadlocks in Mysql / innodb?

Try MaatKit. It has a deadlock logger.

"SHOW ENGINE INNODB STATUS" from the MySQL Command line client (not a query browser) will give you info on deadlocks.

Deadlocks can also be caused by uncommitted transactions (usually program bugs) and the person who is running the uncommitted transaction will not see the problem as they will be working fine (through their data will not be committed).

Try using MONyog. Enable MONyog's "Deadlock Monitoring" option to trace the deadlocks reported by INNODB STATUS. MONyog will send an alert to the user when a new deadlock occur.

http://dev.mysql.com/doc/refman/5.0/en/innodb-error-codes.html

1213 (ER_LOCK_DEADLOCK)

Transaction deadlock. You should rerun the transaction.